RE: Define Continuous DC Voltage - defibrillation
For those who want to skip it, this is not product safety, just a digression from the electric shock topic. As for why the chest thumping works, take the heel of your hand and whack yourself on the side of the head. You'll notice the effect as quite a few cells depolarize. That's the general idea. If you get the heart's attention without doing serious damage, it may pause and restart. As for the PQRST stuff, you asked for it. Now we are getting into vector graphics. Picture two cells, side by side, and depolarize one. You can imagine a time related voltage vector appear and go away. Now picture more cells, and depolarization flowing in a wave across them. The vector gets more interesting both in direction and time. Next, go to three dimensions and place it in a chest. That's what we are working with. Put electrodes on the arms and watch it on a scope and you will get an EKG. Of course you only have one dimension (plus time) represented on the scope. Lets try a few more to get images of that vector in other dimensions. In fact, we do it twelve times to get the standard 12 lead EKG recording. Namely: I - left arm to right arm II - left foot to right arm III - left foot to left arm AVR - right arm to (feet, left arm) AVL - left arm to (feet, right arm) AVF - left foot to (arms, right foot) V1 thru V6 - measurements from leads spread across the chest from between the nipples to the right of the sternum around beneath the left breast to the side of the chest. Each lead one at a time is measured to all limb leads connected together. If you can picture it, the first six measurements give six vector readings in the plane of the limbs, the second six give vector readings in a quadrant cross section of the chest perpendicular to the first six. You actually get a pretty good set of three dimensional readings. Now. Put an arrow through a board, throw it in the ocean and watch what it does as a nice wave goes by. Describe the motion of that vector to someone and see if he can deduce what the wave looks like. Its not random. As each similar wave goes by, you get the same vector path. You can even match vector paths with different types of waves. That's what we do with an EKG. In fact there is a connection between heart activity and the waveshape. However it's sort of remote. What really happens is, we find a normal heart generates a typical pattern. Consider heart disease like an AV block and the pattern changes. That's what its all about. Pattern recognition. A good electrocardiologist has this immense image recognition system in his head and matches EKG patterns to disease. He will in fact generate a picture of where the vector is pointing in time and space and use it to imagine weak or damaged tissue affecting or modifying its path. All that leads to the scope trace and talking about it. If we take the I lead as the typical view and start describing it time wise, we start with P, a small positive hump which corresponds with the atrial contraction Q R S, the negative, positive, negative pulse caused by ventricular contraction and the movement of the voltage vector during that time. T, another smaller slower hump from the repolarization of the ventricles I can't help mentioning an EKG machine I once had which was absolutely amazing. It had NO amplifiers. It was called an Einthoven string galvanometer. It consisted of a large C shaped magnet whose poles tapered down to a very narrow gap. Between that gap stretched a fine gold plated glass fiber which connected to the attenuator (that's right attenuator) and lead selector. There was a hole drilled from the top of the C through the tips of the poles and out the bottom with a light source on one side and moving photo film on the other. It produced a strip chart recording of the movement of the fiber, which of course was the EKG current deflected by the magnetic field. The machine used electricity, for the light bulb and the film motor. It's amazing to think of the skill and ingenuity used to make a millivolt recorder back in those days. If I'm not mistaken, Einthoven was the inventor of the 12 lead EKG recording technique. Bob Johnson -Original Message- From: Bill Owsley [mailto:ows...@cisco.com] Sent: Tuesday, November 20, 2001 12:53 PM To: robertj; 'Bill Owsley'; 'Gary McInturff'; 'Gregg Kervill'; 'Rich Nute' Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage - defibrillation excellent - now if you'll go through the PQRST complex also... - Bill Robert, Thanks for this very interesting piece of data. I've often wonder what atrioventricular fibrillation is, you provide some insight on that as well. If it is a reset of sorts then how did the thumping of the chest ever work? I suppose it can also fall into the category of just being better than nothing at all. I can be learned wrong and always look for a better understanding. Its been awhile but I believe the information came from one
RE: Define Continuous DC Voltage - defibrillation
At 12:56 PM 11/20/2001 , Gary McInturff wrote: urn:schemas-microsoft-com:office:office xmlns:w = urn:schemas-microsoft-com:office:word xmlns:st1 = urn:schemas-microsoft-com:office:smarttags Robert, Thanks for this very interesting piece of data. I've often wonder what atrioventricular fibrillation is, you provide some insight on that as well. If it is a reset of sorts then how did the thumping of the chest ever work? I suppose it can also fall into the category of just being better than nothing at all. I have learned the chest thump, the pre-cordial thump, is for witnessed events. ex: Why doesn't CPR teach the pre-cordial thump? The pre-cordial thump is a technique that involves a firm blow to the chest above the heart using a closed 'fist'. This method is only taught in particular settings, for example the electrical industry and it is recommended that the pre-cordial thump only be administered in the event of an arrest witnessed by an individual trained in the procedure. Furthermore, ARC guidelines recommend that the pre-cordial thump is not a technique suitable for laypeople to be trained in or to administer. http://www.cpr2000.qas.qld.gov.au/faq/ or MEF influences pacemaker rate, causes diastolic depolarisation, and affects action potential repolarisation. It contributes to the positive chronotropic response of the heart to stretch, transient-stretch induced ectopic excitation (including sudden cardiac death after moderate precordial impact - Commotio cordis) and arrhythmogenesis in pressure or volume overloaded hearts. On the other hand, if used appropriately, pre-cordial impact can be a highly efficient means of mechanical pacemaking and cardioversion. Mechanisms of cardiac MEF include stretch-activation of ion channels, mechanical modulation of Ca2+ handling, and interaction with mechano-sensitive non-myocytes of the heart. We study these mechanisms in isolated cardiac cells, cell pairs, culture and tissue. Methods include the single and double whole cell patch clamp techniques, fluorescence microscopy, and optical mapping (currently under development). Interventions involve axial stretch of isolated cells, swelling, local membrane deformation, pharmacological block of ion channels, etc. As part of Professor Denis Nobles BHF Chair for Cardiovascular Physiology we also make extensive use of mathematical modelling for data interpretation, hypothesis formation and design of experimental protocols. http://www.physiol.ox.ac.uk/Graduate_Studies/Research_Interests/kohl2000.html It is related to the rare newspaper article of someone getting hit in the chest with a ball and dropping dead. Speculation has it that the timing was un-lucky and hit at the moment that the heart timing could be stopped. The pre-cordial thump is the reverse. EMT's in this state are not taught the technique. - Bill I can be learned wrong and always look for a better understanding. Its been awhile but I believe the information came from one of the product safety seminars in the Seattle (Rich N. I'm staring pretty hard at you for the moment) area and I don't know really remember the speaker, but it made a great deal of sense to me at the time and obviously most of it stuck with me. (You'll notice I am not taking any blame even if my information is wrong) Thanks Gary -Original Message- From: robertj [mailto:robe...@ma.ultranet.com] Sent: Tuesday, November 20, 2001 9:12 AM To: 'Bill Owsley'; 'Gary McInturff'; 'Gregg Kervill'; 'Rich Nute' Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage - defibrillation I also have not encountered the theory about chest compression controlling fibrillation. Since defibrillation is also controlled during open heart surgery by paddles directly applied to the heart and through the use of wire catheters from implantable defibrillators, it is not the only means. I thought it might be interesting to describe the heart function in electrical terms since that is the basis of understanding for most of us in this group. Heart muscle can be viewed as a simple free running flip-flop oscillator. When cut into pieces, each piece of heart muscle will automatically fire (contract) at its own natural rate. It can be triggered earlier by input from neighboring tissue. Once it fires, it goes through a relaxation stage when it is quite resistant to triggering by neighboring tissue. This firing at a cellular level is call depolarization. It is caused by the cell wall suddenly becoming permeable to sodium and potassium ions and loosing its charge (which of course is a current flow). The cell then takes time to recharge by pumping ions back across the cell wall. The master clock for the heart is the sinoatrial (SA) node (the sinus node mentioned by Gary). This node sets the pace for the heart in response to assorted hormone and brain inputs. It is located in the right atrium. Remember the heart has four chambers. The right atrium is a collecting spot
RE: Define Continuous DC Voltage - defibrillation
Robert, Thanks for this very interesting piece of data. I've often wonder what atrioventricular fibrillation is, you provide some insight on that as well. If it is a reset of sorts then how did the thumping of the chest ever work? I suppose it can also fall into the category of just being better than nothing at all. I can be learned wrong and always look for a better understanding. Its been awhile but I believe the information came from one of the product safety seminars in the Seattle (Rich N. I'm staring pretty hard at you for the moment) area and I don't know really remember the speaker, but it made a great deal of sense to me at the time and obviously most of it stuck with me. (You'll notice I am not taking any blame even if my information is wrong) Thanks Gary -Original Message- From: robertj [mailto:robe...@ma.ultranet.com] Sent: Tuesday, November 20, 2001 9:12 AM To: 'Bill Owsley'; 'Gary McInturff'; 'Gregg Kervill'; 'Rich Nute' Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage - defibrillation I also have not encountered the theory about chest compression controlling fibrillation. Since defibrillation is also controlled during open heart surgery by paddles directly applied to the heart and through the use of wire catheters from implantable defibrillators, it is not the only means. I thought it might be interesting to describe the heart function in electrical terms since that is the basis of understanding for most of us in this group. Heart muscle can be viewed as a simple free running flip-flop oscillator. When cut into pieces, each piece of heart muscle will automatically fire (contract) at its own natural rate. It can be triggered earlier by input from neighboring tissue. Once it fires, it goes through a relaxation stage when it is quite resistant to triggering by neighboring tissue. This firing at a cellular level is call depolarization. It is caused by the cell wall suddenly becoming permeable to sodium and potassium ions and loosing its charge (which of course is a current flow). The cell then takes time to recharge by pumping ions back across the cell wall. The master clock for the heart is the sinoatrial (SA) node (the sinus node mentioned by Gary). This node sets the pace for the heart in response to assorted hormone and brain inputs. It is located in the right atrium. Remember the heart has four chambers. The right atrium is a collecting spot for the returning blood and when it contracts, moves the blood next door to the right ventricle. The right ventricle pumps into the lungs. The left atrium holds returning oxygenated blood and pushes it into the left ventricle which pumps into the rest of the body. Obviously the ventricles are the workhorses. When the sinoatrial node fires, a wave of depolarization spreads over both atria (1/10 of a second), but is protected from reaching the ventricles by a layer of insulation. At the base of the right atrium it reaches the atrioventricular (AV) node. This is a delay line (another 1/10 of a second) and passes the signal to the left and right bundle branches which are special conductors to get the signal quickly to all parts of the ventricles. The AV delay provides the time for the atria to finish filling the ventricles before the much more significant contraction of the ventricles. Since all these conductors are live tissues, injury or irritation, depending on where it occurs, can cause all sorts of problems like fast or slow rhythms, lack of coordination of atria and ventricles, etc. One solution is implantable pacemakers which in their simplest forms electrically trigger the ventricles (the atria are left to themselves since they are not as important). Fibrillation occurs when something (like electric shock or irritation) triggers a piece of heart muscle. This in turn triggers neighboring cells. Unfortunately when the coordinated signal arrives from elsewhere, the cells which have just fired can't respond since they have not gone through their refractory period. These misfired cells then wait (while other parts are recovering) and having waited too long, fire on their own again. When several locations of the heart are doing this, the heart just quivers instead of making a coordinated pumping effort. The fix is to provide an electrical jolt which doesn't bother with triggering, it just hits all the cells with enough energy to force depolarization anyway. Then all cells together go through their refractory period and are ready for a coordinated trigger (if it still exists). This is why very high shock levels can avoid causing fibrillation. Defibrillators have come a long way from the old days when they just applied a severe 60 cycle AC shock. These days they try to provide a minimal level impulse coordinated with any residual heart beat to force the heart into unified action. The impulse can be applied with external paddles, and now is available as a built
RE: Define Continuous DC Voltage - defibrillation
excellent - now if you'll go through the PQRST complex also... - Bill At 12:11 PM 11/20/2001 , robertj wrote: I also have not encountered the theory about chest compression controlling fibrillation. Since defibrillation is also controlled during open heart surgery by paddles directly applied to the heart and through the use of wire catheters from implantable defibrillators, it is not the only means. I thought it might be interesting to describe the heart function in electrical terms since that is the basis of understanding for most of us in this group. Heart muscle can be viewed as a simple free running flip-flop oscillator. When cut into pieces, each piece of heart muscle will automatically fire (contract) at its own natural rate. It can be triggered earlier by input from neighboring tissue. Once it fires, it goes through a relaxation stage when it is quite resistant to triggering by neighboring tissue. This firing at a cellular level is call depolarization. It is caused by the cell wall suddenly becoming permeable to sodium and potassium ions and loosing its charge (which of course is a current flow). The cell then takes time to recharge by pumping ions back across the cell wall. The master clock for the heart is the sinoatrial (SA) node (the sinus node mentioned by Gary). This node sets the pace for the heart in response to assorted hormone and brain inputs. It is located in the right atrium. Remember the heart has four chambers. The right atrium is a collecting spot for the returning blood and when it contracts, moves the blood next door to the right ventricle. The right ventricle pumps into the lungs. The left atrium holds returning oxygenated blood and pushes it into the left ventricle which pumps into the rest of the body. Obviously the ventricles are the workhorses. When the sinoatrial node fires, a wave of depolarization spreads over both atria (1/10 of a second), but is protected from reaching the ventricles by a layer of insulation. At the base of the right atrium it reaches the atrioventricular (AV) node. This is a delay line (another 1/10 of a second) and passes the signal to the left and right bundle branches which are special conductors to get the signal quickly to all parts of the ventricles. The AV delay provides the time for the atria to finish filling the ventricles before the much more significant contraction of the ventricles. Since all these conductors are live tissues, injury or irritation, depending on where it occurs, can cause all sorts of problems like fast or slow rhythms, lack of coordination of atria and ventricles, etc. One solution is implantable pacemakers which in their simplest forms electrically trigger the ventricles (the atria are left to themselves since they are not as important). Fibrillation occurs when something (like electric shock or irritation) triggers a piece of heart muscle. This in turn triggers neighboring cells. Unfortunately when the coordinated signal arrives from elsewhere, the cells which have just fired can t respond since they have not gone through their refractory period. These misfired cells then wait (while other parts are recovering) and having waited too long, fire on their own again. When several locations of the heart are doing this, the heart just quivers instead of making a coordinated pumping effort. The fix is to provide an electrical jolt which doesn t bother with triggering, it just hits all the cells with enough energy to force depolarization anyway. Then all cells together go through their refractory period and are ready for a coordinated trigger (if it still exists). This is why very high shock levels can avoid causing fibrillation. Defibrillators have come a long way from the old days when they just applied a severe 60 cycle AC shock. These days they try to provide a minimal level impulse coordinated with any residual heart beat to force the heart into unified action. The impulse can be applied with external paddles, and now is available as a built in part of implanted pacemakers so the impulse can be applied directly to the heart using the pacing electrodes. Bob Johnson -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Bill Owsley Sent: Monday, November 19, 2001 1:22 PM To: Gary McInturff; 'Gregg Kervill'; 'Rich Nute' Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage I've never seen cardiac function or resuscitation explained this way... and I'm an EMT-D. The D is for defibrillator and the EMT is for emergency medical technician. And with very few exceptions, the rest of the medical aspects of this discussion have been suspect. As my kids say - don't go there... - Bill At 12:02 PM 11/19/2001 , Gary McInturff wrote: From a few courses several years back. The heart has something called the Sinus node (spelling could be wrong) The responsibility of that node is to control
RE: Define Continuous DC Voltage - defibrillation
I also have not encountered the theory about chest compression controlling fibrillation. Since defibrillation is also controlled during open heart surgery by paddles directly applied to the heart and through the use of wire catheters from implantable defibrillators, it is not the only means. I thought it might be interesting to describe the heart function in electrical terms since that is the basis of understanding for most of us in this group. Heart muscle can be viewed as a simple free running flip-flop oscillator. When cut into pieces, each piece of heart muscle will automatically fire (contract) at its own natural rate. It can be triggered earlier by input from neighboring tissue. Once it fires, it goes through a relaxation stage when it is quite resistant to triggering by neighboring tissue. This firing at a cellular level is call depolarization. It is caused by the cell wall suddenly becoming permeable to sodium and potassium ions and loosing its charge (which of course is a current flow). The cell then takes time to recharge by pumping ions back across the cell wall. The master clock for the heart is the sinoatrial (SA) node (the sinus node mentioned by Gary). This node sets the pace for the heart in response to assorted hormone and brain inputs. It is located in the right atrium. Remember the heart has four chambers. The right atrium is a collecting spot for the returning blood and when it contracts, moves the blood next door to the right ventricle. The right ventricle pumps into the lungs. The left atrium holds returning oxygenated blood and pushes it into the left ventricle which pumps into the rest of the body. Obviously the ventricles are the workhorses. When the sinoatrial node fires, a wave of depolarization spreads over both atria (1/10 of a second), but is protected from reaching the ventricles by a layer of insulation. At the base of the right atrium it reaches the atrioventricular (AV) node. This is a delay line (another 1/10 of a second) and passes the signal to the left and right bundle branches which are special conductors to get the signal quickly to all parts of the ventricles. The AV delay provides the time for the atria to finish filling the ventricles before the much more significant contraction of the ventricles. Since all these conductors are live tissues, injury or irritation, depending on where it occurs, can cause all sorts of problems like fast or slow rhythms, lack of coordination of atria and ventricles, etc. One solution is implantable pacemakers which in their simplest forms electrically trigger the ventricles (the atria are left to themselves since they are not as important). Fibrillation occurs when something (like electric shock or irritation) triggers a piece of heart muscle. This in turn triggers neighboring cells. Unfortunately when the coordinated signal arrives from elsewhere, the cells which have just fired can't respond since they have not gone through their refractory period. These misfired cells then wait (while other parts are recovering) and having waited too long, fire on their own again. When several locations of the heart are doing this, the heart just quivers instead of making a coordinated pumping effort. The fix is to provide an electrical jolt which doesn't bother with triggering, it just hits all the cells with enough energy to force depolarization anyway. Then all cells together go through their refractory period and are ready for a coordinated trigger (if it still exists). This is why very high shock levels can avoid causing fibrillation. Defibrillators have come a long way from the old days when they just applied a severe 60 cycle AC shock. These days they try to provide a minimal level impulse coordinated with any residual heart beat to force the heart into unified action. The impulse can be applied with external paddles, and now is available as a built in part of implanted pacemakers so the impulse can be applied directly to the heart using the pacing electrodes. Bob Johnson -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Bill Owsley Sent: Monday, November 19, 2001 1:22 PM To: Gary McInturff; 'Gregg Kervill'; 'Rich Nute' Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage I've never seen cardiac function or resuscitation explained this way... and I'm an EMT-D. The D is for defibrillator and the EMT is for emergency medical technician. And with very few exceptions, the rest of the medical aspects of this discussion have been suspect. As my kids say - don't go there... - Bill At 12:02 PM 11/19/2001 , Gary McInturff wrote: From a few courses several years back. The heart has something called the Sinus node (spelling could be wrong) The responsibility of that node is to control the timing of the electric wave front if you will. The heart actually has about three pulses. Looking at a heart
RE: Define Continuous DC Voltage
I've never seen cardiac function or resuscitation explained this way... and I'm an EMT-D. The D is for defibrillator and the EMT is for emergency medical technician. And with very few exceptions, the rest of the medical aspects of this discussion have been suspect. As my kids say - don't go there... - Bill At 12:02 PM 11/19/2001 , Gary McInturff wrote: From a few courses several years back. The heart has something called the Sinus node (spelling could be wrong) The responsibility of that node is to control the timing of the electric wave front if you will. The heart actually has about three pulses. Looking at a heart waveform on a monitor you will see a small blip, big blip, and another smaller blip (those all being medical terms naturally). Those are the QRS waves, and sweep across the heart, from the input side to the output, although the big blip' is the main blood moving event. I no longer remember exactly what each of the pulses does, but all three are needed for the pumping of blood through the heart chambers, and the sinus node does all the time for these events. When low level current disrupts this timing sequence the heart starts to fibrillate - it beats unrhymtically and quivers not only does it not pump blood but it works itself into exhaustion. The node needs to be allowed to resynchronize. That is done with a high current applied to a defibrillator paddle from one side of the chest to the other. When this is done it is not the current through the heart that is effective but the current through the muscles of the chest that are effective. The current causes the muscles to constrict hard enough to squeeze the heart muscle and prevent it from the uncontrolled and uncoordinated pulsing. The current is release, the muscles relax, and it is hoped that the sinus node re-takes control of the heart. This is the reason that the old method of reviving someone by slamming them in the chest worked. It forced the heart to stop long enough for the sinus node to reestablish itself. People that work around high voltage are more prone to death by falling from the high voltage lines, or internal burns that actual heart failure do to heart fibrillation. Gary -Original Message- From: Gregg Kervill [mailto:gkerv...@eu-link.com] Sent: Tuesday, November 13, 2001 1:12 PM To: 'Rich Nute' Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage Hi Rich There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. - I'll try and find it - it may have called the fatal current circa 72-5 published in the UK B-I-G SNIP INFORMATION OVERLOAD!! I'm squeamish So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Hang on - I'm trying to quote from an article I read in the early 70's - and the figures were from the article. I'm sure it was from Tex - we had a number of the big valve 'scopes (plugins and more than 100 valves) - wonderful things and the only ones that allowed a delay longer than the TB sweep. I'll try to dig the article out - I found it very useful - particularly since the safety standards at that time were pretty Spartan. Thank goodness they have - and continue to help and provide guidance. Best regards Gregg --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web
RE: Define Continuous DC Voltage
From a few courses several years back. The heart has something called the Sinus node (spelling could be wrong) The responsibility of that node is to control the timing of the electric wave front if you will. The heart actually has about three pulses. Looking at a heart waveform on a monitor you will see a small blip, big blip, and another smaller blip (those all being medical terms naturally). Those are the QRS waves, and sweep across the heart, from the input side to the output, although the big blip' is the main blood moving event. I no longer remember exactly what each of the pulses does, but all three are needed for the pumping of blood through the heart chambers, and the sinus node does all the time for these events. When low level current disrupts this timing sequence the heart starts to fibrillate - it beats unrhymtically and quivers not only does it not pump blood but it works itself into exhaustion. The node needs to be allowed to resynchronize. That is done with a high current applied to a defibrillator paddle from one side of the chest to the other. When this is done it is not the current through the heart that is effective but the current through the muscles of the chest that are effective. The current causes the muscles to constrict hard enough to squeeze the heart muscle and prevent it from the uncontrolled and uncoordinated pulsing. The current is release, the muscles relax, and it is hoped that the sinus node re-takes control of the heart. This is the reason that the old method of reviving someone by slamming them in the chest worked. It forced the heart to stop long enough for the sinus node to reestablish itself. People that work around high voltage are more prone to death by falling from the high voltage lines, or internal burns that actual heart failure do to heart fibrillation. Gary -Original Message- From: Gregg Kervill [mailto:gkerv...@eu-link.com] Sent: Tuesday, November 13, 2001 1:12 PM To: 'Rich Nute' Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage Hi Rich There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. - I'll try and find it - it may have called the fatal current circa 72-5 published in the UK B-I-G SNIP INFORMATION OVERLOAD!! I'm squeamish So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Hang on - I'm trying to quote from an article I read in the early 70's - and the figures were from the article. I'm sure it was from Tex - we had a number of the big valve 'scopes (plugins and more than 100 valves) - wonderful things and the only ones that allowed a delay longer than the TB sweep. I'll try to dig the article out - I found it very useful - particularly since the safety standards at that time were pretty Spartan. Thank goodness they have - and continue to help and provide guidance. Best regards Gregg --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: Define Continuous DC Voltage
Hi Rich There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. - I'll try and find it - it may have called the fatal current circa 72-5 published in the UK B-I-G SNIP INFORMATION OVERLOAD!! I'm squeamish So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Hang on - I'm trying to quote from an article I read in the early 70's - and the figures were from the article. I'm sure it was from Tex - we had a number of the big valve 'scopes (plugins and more than 100 valves) - wonderful things and the only ones that allowed a delay longer than the TB sweep. I'll try to dig the article out - I found it very useful - particularly since the safety standards at that time were pretty Spartan. Thank goodness they have - and continue to help and provide guidance. Best regards Gregg --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
Hi John: Also consider that the rectifier will very probably fail due to excessive reverse voltage under the fault condition, thus allowing fault current to flow through the transformer winding. Will the rectifier fail open or short? This SELV grounding scheme certainly doesn't fit the conventional safety model for predictability and reliability. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in 20042313.paa09...@epgc196.sdd.hp.com) about 'AW: Define Continuous DC Voltage', on Wed, 14 Nov 2001: When the fault occurs between the mains and the ungrounded SELV pole, 240 volts will appear across the aggregate 1.25-ohm resistance. There is no single component with an impedance of 1.25 ohms. Clearly, the aggregate current is sufficiently low to easily operate the 3-amp mains fuse, E/R or 192 amps. However, not a wire or PWB trace could carry 192 amps. So, this scenario is impossible. Absolutely not. The 3 A fuse will open in less than 10 ms at 192 A (published time/current curves don't go as high as 64 times rated current, even for HBC fuses) and any reasonable conductor will carry 192 A for that period (not necessarily undamaged). Current-carrying capacity is a peculiar concept. The standard or conventional values for wires and cables are very low, because these currents can flow for years. Consider the currents that flow through the very thin lead wires in semiconductors, and the inrush currents that flow through PCB traces to power supply filter capacitors. Also consider that the rectifier will very probably fail due to excessive reverse voltage under the fault condition, thus allowing fault current to flow through the transformer winding. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
Hi John: I presume that the fault current path for the ungrounded SELV pole must be routed through the SELV source to ground as that path is the lowest impedance path to ground. It seems to me that the fault current would have to pass through the transformer winding. In some cases, the fault current may have to pass backwards through the rectifier to ground -- which is an impossibility. I don't understand that. If the fault current can't flow through the source, it will flow through the load. That is OK, if the product remains safe. It doesn't have to work after such a fault has occurred. The load impedance of many SELV circuits is relatively high. If a mains fault should occur to the ungrounded SELV pole, then the impedance of the load must either: 1) carry the fault current until the overcurrent device operates, or 2) present a sufficiently low impedance relative to the fault impedance such that the voltage on the SELV circuits does not exceed the SELV rating. For example, consider a 240-volt mains, a 3-amp mains fuse, and a 5-volt, 4-amp SELV. To operate the fuse within 1 minute, the fault current must be at least 6 amps. The aggregate 5-volt load impedance is E/I or 1.25 ohms. When the fault occurs between the mains and the ungrounded SELV pole, 240 volts will appear across the aggregate 1.25-ohm resistance. There is no single component with an impedance of 1.25 ohms. Clearly, the aggregate current is sufficiently low to easily operate the 3-amp mains fuse, E/R or 192 amps. However, not a wire or PWB trace could carry 192 amps. So, this scenario is impossible. We need 6 amps to operate the fuse. So, we need the aggregate SELV impedance to be E/I, 240/6, or 40 ohms. 40-ohm devices in a 5-volt circuit are reasonable. However, such devices would be rated no more than 1/2-watt (for the 5-volt circuit). When the fault occurs, 240 volts is applied across a 40-ohm, 1/2 watt resistance. Since 240 volts, 40 ohms, and 6 amps is 1440 watts, the question is: What opens first, the resistor or the fuse? If the resistor opens, then the SELV voltage goes to 240 volts, and the scheme is unsafe. So, in this scenario, the 5-volt circuit would need to include a 40-ohm, 1400-watt (240 x 6) resistor to carry the fault current until the fuse operates. My conclusion is that relying on the SELV load to operate the primary protective device is not practicable. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: Define Continuous DC Voltage
I knew someone was going to ask this.. A few years back, I was attending a UL 1950 seminar in Minneapolis. One of the presenters (a fellow named 'Bahra') happened to mention that UL has a specification for the 'electric chair'. The operating current was quoted by him to not exceed 70ma. I jotted down this figure, but unfortunately the voltage and clause was not mentioned, and I was hesitant to ask. The topic at the time was AC electric shock. In my copy of the slide presentation (slide 25), I noted the effects: (for AC electric shock, verbatim, with figures added as quoted) -perception .05 to .5ma -reaction 2 to 5ma -inability to let-go 5 to 20ma -ventricular fibrillation 20ma + -cell damage 20 to 70ma -burn hazard(high frequency) No voltages or frequency were specified.. btw, I lived in Portland, Or. in the 70's and had a friend that worked at the Tek Wilsonville plant. He had the most amazing set of tools...I think I kinda bonded with him. Now, I have even more tools than he did.. Tim Allen porking in background Kyle Ehler KCOIQE mailto:kyle.eh...@lsil.com Assistant Design Engineer LSI Logic Storage Systems Div. 3718 N. Rock Road U.S.A. Wichita, Kansas 67226 Ph. 316 636 8657 Fax 316 636 8321 -Original Message- From: Dan Kinney (A) [mailto:dan.kin...@heapg.com] Sent: Tuesday, November 13, 2001 3:56 PM To: Rich Nute; gkerv...@eu-link.com Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage Does anyone know what voltage is used in electric chairs? Just Curious. Dan Kinney Horner APG Indianapolis -Original Message- From: Rich Nute [SMTP:ri...@sdd.hp.com] Sent: Tuesday, November 13, 2001 2:08 PM To: gkerv...@eu-link.com Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage Hi Gregg: There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. Electric energy causes various injuries to the body depending on the magnitude of the energy. Only two of the injuries can lead to a fatality. The two injuries are fibrillation of the heart, and overheating of internal organs, especially the liver. Fibrillation is caused by ac current in the range of 50 mA to 500 mA (external connections) where the current pathway through the body includes the chest (and the heart). Above 500 mA, fibrillation is not a likely consequence. (And, I believe I am correct in asserting that dc cannot cause fibrillation.) Overheating of internal organs is a function of power dissipated in the body, where the body impedance can be taken as 1000 ohms. The power required depends on the time of contact. Electric utility linemen are subject to such injury. Consider 1 ampere through 1000 ohms is 1000 watts! (The electric chair kills by over-heating the internal organs, not by fibrillation.) So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Best regards, Rich
Re: AW: Define Continuous DC Voltage
I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in 20041710.jaa08...@epgc196.sdd.hp.com) about 'AW: Define Continuous DC Voltage', on Wed, 14 Nov 2001: A SELV circuit can be grounded. As a result of connecting the SELV to ground, the name of the circuit may change to PELV or FELV, depending on the end- product standard. If the end-product standard is IEC 60960, then the circuit name remains SELV. No. FELV has only basic insulation and grounding; it is not grounded SELV. PELV is grounded SELV. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in 20041912.laa08...@epgc196.sdd.hp.com) about 'AW: Define Continuous DC Voltage', on Wed, 14 Nov 2001: I presume that the fault current path for the ungrounded SELV pole must be routed through the SELV source to ground as that path is the lowest impedance path to ground. It seems to me that the fault current would have to pass through the transformer winding. In some cases, the fault current may have to pass backwards through the rectifier to ground -- which is an impossibility. I don't understand that. If the fault current can't flow through the source, it will flow through the load. That is OK, if the product remains safe. It doesn't have to work after such a fault has occurred. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
FW: AW: Define Continuous DC Voltage
Keep in mind that failure of the earthing can also be an undetected fault. The intent is to provide two levels of protection, two layers of insulation or one layer of insulation plus earthing. In each case, failure of one level may go undetected until failure of the second produces a hazard. Often double insulation is preferred because earthing is sometimes intentionally bypassed by those who have old building wiring or wish to use two wire extension cords. In the US, cheater plugs for this purpose are commonly available. In this case the earthing failure may not be undetected, but is present nevertheless. Note also that in IEC 60950, earthing of SELV circuits is permitted. Certain testing like ampacity of the earthing path and conditions such as transient levels are adjusted accordingly. It is wise to treat all interconnections to other equipment as circuits which may be either earthed or floating unless you also have direct control over the destination circuit. Bob -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of John Woodgate Sent: Wednesday, November 14, 2001 3:58 AM To: emc-p...@majordomo.ieee.org Subject: Re: AW: Define Continuous DC Voltage I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in 20040041.qaa06...@epgc196.sdd.hp.com) about 'AW: Define Continuous DC Voltage', on Tue, 13 Nov 2001: Hi John: SELV can protect under single fault conditions. BUT, as I tried to explain, under some conditions, it can allow a single fault *to persist undetected*, until eventually a second, unrelated fault occurs which then results in a serious hazard. This is a problem of the double-insulation scheme: one cannot know when the first insulation has failed. So, your argument not only applies to SELV but also to ungrounded accessible metal parts and any other double- insulation scheme. If we pursue your argument, then we should outlaw double insulation as an acceptable scheme of protection against electric shock, independent of SELV. No, you are 'extending the argument' until it looks unjustified and then using that as a hook for your critique. I said quite clearly that failure of double or reinforced insulation is acceptable because failure of it has an acceptably low probability. And, we should add a new criterion that failure of any safeguard should be obvious to the operator *without* presenting a hazard to the operator. An interesting design problem. With PELV, this does not happen: the grounding ensures that the protective device operates. This scheme requires that the path between the ungrounded PELV pole and the grounded PELV pole be capable of carrying the fault current until the protective device operates. In other words, the ungrounded PELV pole must carry 25 amps for 1 minute (or appropriate criteria). Yes, 'appropriate criteria'. 25A for 1 min is an extreme criterion. Let's go to the other extreme, 150 mA for 100 ms (protection by RCD). In turn, this means the fault current, 25 amps, must flow from the ungrounded PELV pole through the PELV source to the grounded PELV pole. In my experience, there are few PELV circuits that can meet this criterion. In the PELV circuits I have worked with, the 25 A would cause the PELV source to open before the operation of a protective device, and the mains voltage would appear on the PELV ungrounded pole. Yes, because you have deliberately chosen a huge fault current, which is quite unrealistic in most cases. Well, perhaps I have made it clearer now. My beef with SELV is the ban on grounding, whereas PELV which is grounded AND double/reinforced insulated is clearly safer for systems extended in space. Agreed. In the products I deal with, this is our construction. However, we do not test the capability of the ungrounded PELV pole to carry fault current. Well, you might consider *designing* it to carry a realistic fault current, then there is probably no overwhelming need to test. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server
Re: AW: Define Continuous DC Voltage
Hi John: SELV can protect under single fault conditions. BUT, as I tried to explain, under some conditions, it can allow a single fault *to persist undetected*, until eventually a second, unrelated fault occurs which then results in a serious hazard. This is a problem of the double-insulation scheme: one cannot know when the first insulation has failed. So, your argument not only applies to SELV but also to ungrounded accessible metal parts and any other double- insulation scheme. If we pursue your argument, then we should outlaw double insulation as an acceptable scheme of protection against electric shock, independent of SELV. No, you are 'extending the argument' until it looks unjustified and then using that as a hook for your critique. Your thesis is that: Ungrounded SELV can under some conditions, allow a single fault *to persist undetected*, until eventually a second, unrelated fault occurs which then results in a serious hazard. You are applying this principle only for SELV. The solution is to ground the SELV. I did indeed extend the argument, not to make it look unjustified but to understand why the principle applies only to SELV and not to similar constructions. My remarks certainly were not clear on this point. I said quite clearly that failure of double or reinforced insulation is acceptable because failure of it has an acceptably low probability. Now I am extending the argument in the other direction. If the failure of double or reinforced insulation has an acceptably low probability of failure, then if SELV is double- or reinforced-insulated from a higher voltage, why must it be grounded? I presume the answer lies in the proviso of under some conditions. I guess I missed those conditions in one of your messages. With PELV, this does not happen: the grounding ensures that the protective device operates. This scheme requires that the path between the ungrounded PELV pole and the grounded PELV pole be capable of carrying the fault current until the protective device operates. In other words, the ungrounded PELV pole must carry 25 amps for 1 minute (or appropriate criteria). Yes, 'appropriate criteria'. 25A for 1 min is an extreme criterion. Let's go to the other extreme, 150 mA for 100 ms (protection by RCD). Yes, appropriate criteria. The worst-case would be 25 amps. In most cases, the SELV circuit is on the load side of the primary circuit protection and thus would only be subject to twice the rated current of the equipment overcurrent device. (In the USA one cannot rely on a building installation RCD/GFCI for protection from a single fault in a product. The RCD/GFCI can be used for protection of a double fault in a product.) Well, you might consider *designing* it to carry a realistic fault current, then there is probably no overwhelming need to test. Hmm. Design, but no test. This would certainly present a challenge to write such a concept for SELV circuit-carrying capacity into a safety standard. I presume that the fault current path for the ungrounded SELV pole must be routed through the SELV source to ground as that path is the lowest impedance path to ground. It seems to me that the fault current would have to pass through the transformer winding. In some cases, the fault current may have to pass backwards through the rectifier to ground -- which is an impossibility. Now I am wondering about the practicality of this proposal for any part of the SELV circuit except the transformer winding. Best regards, Rich ps: I recall a high-power power supply where the 5-volt SELV winding was a single turn of a robust copper sheet. One end of the copper sheet was grounded. Any insulation fault within the transformer would have been grounded through the copper sheet. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
I read in !emc-pstc that John Woodgate j...@jmwa.demon.co.uk wrote (in bhmfeca9hj87e...@jmwa.demon.co.uk) about 'AW: Define Continuous DC Voltage', on Wed, 14 Nov 2001: I said quite clearly that failure of double or reinforced insulation is acceptable because failure of it has an acceptably low probability. OOPS! That should read: I said quite clearly that double or reinforced insulation is acceptable because failure of it has an acceptably low probability. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
Hi Vito: Could either of you clarify why a double insulated SELV circuit can not be grounded? Is it a 60950 based or based on some other performance(?) based requirements? This requires a bit of history. I don't have all of the history, but I can fill in some of the blanks. IEC 536 (1976) is the base document for equipment classes, i.e., I, II, and III. Class III required the introduction of SELV. IEC 536 was prepared by the same folks who wrote the IEC 364 series of standards on building installations. For these folks, SELV was presumed not to be connected to ground. (If they had been in the USA, these folks would have considered the doorbell circuit as SELV.) The standard did not explicity prohibit SELV from being grounded. The committee was quite shocked to learn that equipment manufacturers were using the concept for low-voltage secondary circuits and were grounding one pole of the SELV. They did have a technical explanation of why grounding SELV was not acceptable (which I have forgotten and, at the time, I considered faulty). In revising IEC 536, the committee then considered the issue of grounding SELV. They decided to retain SELV as ungrounded, and introduced a new concept, PELV (protected extra-low voltage) which was protected by virture of being grounded. They also introduced FELV (functionally-grounded extra-low voltage). The IEC 950 folks ignored IEC 536 -- sort of. They did not adopt PELV, but retained SELV. Instead, they did provide for PELV by specifying Method 3 under SELV circuit requirements. (At one time, several European countries did not accept Method 3.) The IEC 950 definition of SELV includes a note: This definition of SELV CIRCUIT differs from the term SELV as used in IEC 364. A SELV circuit can be grounded. As a result of connecting the SELV to ground, the name of the circuit may change to PELV or FELV, depending on the end- product standard. If the end-product standard is IEC 60960, then the circuit name remains SELV. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
I read in !emc-pstc that vit...@aol.com wrote (in 117.79cc5a2.29233849@ aol.com) about 'AW: Define Continuous DC Voltage', on Tue, 13 Nov 2001: Could either of you clarify why a double insulated SELV circuit can not be grounded? Is it a 60950 based or based on some other performance(?) based requirements? I think the original definition is in IEC60364, certainly not IEC60950, which says that its definition differs from that in IEC60364. The original idea, AIUI, was that a circuit that did not depend on earthing for continued safety was safer than one that required earthing. It seems that the consequences of a fault persisting undetected were not taken into account. There was a great deal of controversy over this matter some years ago, which seems to have stopped once PELV (SELV plus earthing) was introduced. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
John, Rich; Could either of you clarify why a double insulated SELV circuit can not be grounded? Is it a 60950 based or based on some other performance(?) based requirements? thx, vgl In a message dated Tue, 13 Nov 2001 7:51:18 PM Eastern Standard Time, Rich Nute ri...@sdd.hp.com writes: Hi John: .. Well, perhaps I have made it clearer now. My beef with SELV is the ban on grounding, whereas PELV which is grounded AND double/reinforced insulated is clearly safer for systems extended in space. Agreed. In the products I deal with, this is our construction. However, we do not test the capability of the ungrounded PELV pole to carry fault current. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
Hi John: SELV can protect under single fault conditions. BUT, as I tried to explain, under some conditions, it can allow a single fault *to persist undetected*, until eventually a second, unrelated fault occurs which then results in a serious hazard. This is a problem of the double-insulation scheme: one cannot know when the first insulation has failed. So, your argument not only applies to SELV but also to ungrounded accessible metal parts and any other double- insulation scheme. If we pursue your argument, then we should outlaw double insulation as an acceptable scheme of protection against electric shock, independent of SELV. And, we should add a new criterion that failure of any safeguard should be obvious to the operator *without* presenting a hazard to the operator. An interesting design problem. With PELV, this does not happen: the grounding ensures that the protective device operates. This scheme requires that the path between the ungrounded PELV pole and the grounded PELV pole be capable of carrying the fault current until the protective device operates. In other words, the ungrounded PELV pole must carry 25 amps for 1 minute (or appropriate criteria). In turn, this means the fault current, 25 amps, must flow from the ungrounded PELV pole through the PELV source to the grounded PELV pole. In my experience, there are few PELV circuits that can meet this criterion. In the PELV circuits I have worked with, the 25 A would cause the PELV source to open before the operation of a protective device, and the mains voltage would appear on the PELV ungrounded pole. Well, perhaps I have made it clearer now. My beef with SELV is the ban on grounding, whereas PELV which is grounded AND double/reinforced insulated is clearly safer for systems extended in space. Agreed. In the products I deal with, this is our construction. However, we do not test the capability of the ungrounded PELV pole to carry fault current. Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Hi John: Tetanus is a disease caused by a bacillus. Muscles spasm is tetany. Not according to my (American) dictionary. Tetanus has two definitions. The first is the disease or the bacterium that causes the disease. The second is a prolonged contraction of a muscle resulting from rapidly applied repeated motor impulses. This is what happens when a 50-60 Hertz current is applied to the muscle. Reilly uses the word tetanus thusly: ...maximum muscle tension is achieved at an AP (Action Potential) rate of about 80/s, leading to a condition of maximum fusion termed tetanus. Tetany is defined as a condition of physiologic calcium imbalance marked by tonic spasm of muscles and often associated with deficient parathyroid secretion. Best regards, Rich ref: J. Patrick Reilly, Applied Biolectricity from Electrical Stimlation to Electropathology. ISBN 0-387-98407-0 Springer-Verlag, New York --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: Define Continuous DC Voltage
I believe it is 2000-2700V and about 7-10A the value has increased from 1700V and 6A because some prisoners did not die. Regards, Jorge Sarellano TUV PRODUCT SERVICE Compliance Engineer Phone 408-919-3744 Fax 408-919-0585 Have you visited http://www.tuvam.com lately? -Original Message- From: dan.kin...@heapg.com [mailto:dan.kin...@heapg.com] Sent: Tuesday, November 13, 2001 1:56 PM To: Rich Nute; gkerv...@eu-link.com Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage Does anyone know what voltage is used in electric chairs? Just Curious. Dan Kinney Horner APG Indianapolis -Original Message- From: Rich Nute [SMTP:ri...@sdd.hp.com] Sent: Tuesday, November 13, 2001 2:08 PM To: gkerv...@eu-link.com Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage Hi Gregg: There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. Electric energy causes various injuries to the body depending on the magnitude of the energy. Only two of the injuries can lead to a fatality. The two injuries are fibrillation of the heart, and overheating of internal organs, especially the liver. Fibrillation is caused by ac current in the range of 50 mA to 500 mA (external connections) where the current pathway through the body includes the chest (and the heart). Above 500 mA, fibrillation is not a likely consequence. (And, I believe I am correct in asserting that dc cannot cause fibrillation.) Overheating of internal organs is a function of power dissipated in the body, where the body impedance can be taken as 1000 ohms. The power required depends on the time of contact. Electric utility linemen are subject to such injury. Consider 1 ampere through 1000 ohms is 1000 watts! (The electric chair kills by over-heating the internal organs, not by fibrillation.) So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: Define Continuous DC Voltage
There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. I think I will try not the check that out. Gregg PLEASE NOTE NEW NUMBERS P.O. Box 310, Reedville, Virginia 22539 USA Phone: (804) 453-3141 Fax: (804) 453-9039 Web: www.test4safety.com -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of jrbar...@lexmark.com Sent: Monday, November 12, 2001 8:16 AM To: 'EMC-PSTC Discussion Group' Subject: RE: Define Continuous DC Voltage From my reading on the subject, EN 60950 has different Safety Extra-Low Voltage (SELV) limits for alternating current (AC) and direct current (DC) because the human body reacts to them differently. AC makes your muscles contract, so you tend to hang onto the source of the electric shock. DC makes you push away, removing contact, but you may fall or otherwise hurt yourself as you jerk away from the source of the shock. I have heard hams (amateur radio operators) tell of picking themselves off the floor, clear across the room, after accidently touching the plate supply of a tube radio. I found an article in Electronics magazine, published between 1940 and 1945 (I can't find the article right now), on a study that was done on let-go current. In this study the subjects (something like 100 young males) would grab a 1/4 wire with one hand, and put their other hand on a copper or brass plate. The experimenter would apply a voltage between the wire and the plate, giving the subject a shock. Then the subject would try to let go of the wire. If they couldn't, they could open the circuit just by lifting their hand from the plate. If the subject could let go of the wire, the experimenter would increase the voltage and they would try the experiment again. As I recall the experiments were done mainly at 50 and 60Hz, with some done at DC and low frequencies, and others up to 10kHz. The results of the study were that let-go current was lowest in the 40-100Hz range, and ranged from 15mA up to about 100mA. (I got the impression that some of the young men were trying to show how macho they were...) The let-go current increased as the frequency increased above 100Hz, or decreased below 40Hz. For DC the subjects had trouble trying to hold onto the wire, and instead of a shock they felt a heating effect. I have not seen any studies on how much AC superimposed on DC changes the let-go effect to a hang-on effect, and I don't plan to find out for myself if I don't have to... John Barnes Advisory Engineer Lexmark International --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Hi Dan: Does anyone know what voltage is used in electric chairs? Just Curious. I'm sorry you asked. The electric chair is one of the more barbarous methods of execution. The voltage is a function of time, and varies with the execution authority. The voltage is in the range of 1000-2000 volts, sometimes more, sometimes less. For more than you would ever want to know, including the voltage specs, see: http://www.theelectricchair.com/ You will need to use search the site to find voltage and other details. Be sure to read biology of electrocution. Also check out the botched electrocutions. Here are other sites I found as the result of a web search. The descriptions and pictures are gruesome and are not recommended. http://www.geocities.com/CapitolHill/6142/chair.html http://www.albany.edu/~brandon/sparky.html http://hypertextbook.com/facts/NancyRyan.shtml http://hypertextbook.com/facts/AprilDunetz.shtml http://members.aol.com/karlkeys/chair.htm http://www.pdimages.com/X0029.html-ssi http://www.suburbanchicagonews.com/joliet/prisons/chair2.html http://noop.rotten.com/chair/ http://library.thinkquest.org/23685/data/chair.html http://www.capitalcentury.com/1907.html http://www.fcc.state.fl.us/fcc/reports/methods/emappa.html http://www.hatchoo.com/deathrow/ http://www.ariel.com/au/jokes/The_Electric_Chair.html http://northstargallery.com/pages/Electric01.htm This site has some body impedance data taken during several executions. The descriptions and arguments are explicit and gruesome. http://www.dc.state.fl.us/oth/deathrow/drorder.html Calculate the power (E x I) dissipated in the body. Regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Whoops!!! I was thinking wheel chair and on second thought I realized what you were thinking of was a means of intentional electrocution and execution. My mistake! -- From: Dan Kinney (A) dan.kin...@heapg.com To: Rich Nute ri...@sdd.hp.com, gkerv...@eu-link.com Cc: jrbar...@lexmark.com, emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage Date: Tue, Nov 13, 2001, 3:56 PM Does anyone know what voltage is used in electric chairs? Just Curious. Dan Kinney Horner APG Indianapolis -Original Message- From: Rich Nute [SMTP:ri...@sdd.hp.com] Sent: Tuesday, November 13, 2001 2:08 PM To: gkerv...@eu-link.com Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage Hi Gregg: There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. Electric energy causes various injuries to the body depending on the magnitude of the energy. Only two of the injuries can lead to a fatality. The two injuries are fibrillation of the heart, and overheating of internal organs, especially the liver. Fibrillation is caused by ac current in the range of 50 mA to 500 mA (external connections) where the current pathway through the body includes the chest (and the heart). Above 500 mA, fibrillation is not a likely consequence. (And, I believe I am correct in asserting that dc cannot cause fibrillation.) Overheating of internal organs is a function of power dissipated in the body, where the body impedance can be taken as 1000 ohms. The power required depends on the time of contact. Electric utility linemen are subject to such injury. Consider 1 ampere through 1000 ohms is 1000 watts! (The electric chair kills by over-heating the internal organs, not by fibrillation.) So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
I know of at least one that runs off a 12 Volt battery. I think it is a gel-cell but I KNOW it charges off an ordinary 12 Volt charger and it is supposed to be trickled charged nightly, so it is like a lead-acid in that it likes to be constantly charged and doesn't have memory. -- From: Dan Kinney (A) dan.kin...@heapg.com To: Rich Nute ri...@sdd.hp.com, gkerv...@eu-link.com Cc: jrbar...@lexmark.com, emc-p...@majordomo.ieee.org Subject: RE: Define Continuous DC Voltage Date: Tue, Nov 13, 2001, 3:56 PM Does anyone know what voltage is used in electric chairs? Just Curious. Dan Kinney Horner APG Indianapolis -Original Message- From: Rich Nute [SMTP:ri...@sdd.hp.com] Sent: Tuesday, November 13, 2001 2:08 PM To: gkerv...@eu-link.com Cc: jrbar...@lexmark.com; emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage Hi Gregg: There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. Electric energy causes various injuries to the body depending on the magnitude of the energy. Only two of the injuries can lead to a fatality. The two injuries are fibrillation of the heart, and overheating of internal organs, especially the liver. Fibrillation is caused by ac current in the range of 50 mA to 500 mA (external connections) where the current pathway through the body includes the chest (and the heart). Above 500 mA, fibrillation is not a likely consequence. (And, I believe I am correct in asserting that dc cannot cause fibrillation.) Overheating of internal organs is a function of power dissipated in the body, where the body impedance can be taken as 1000 ohms. The power required depends on the time of contact. Electric utility linemen are subject to such injury. Consider 1 ampere through 1000 ohms is 1000 watts! (The electric chair kills by over-heating the internal organs, not by fibrillation.) So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in 20031830.kaa06...@epgc196.sdd.hp.com) about 'AW: Define Continuous DC Voltage', on Tue, 13 Nov 2001: Hi John: I have never been very keen on the concept of SELV, and I am glad to see that others are now recognizing the problems. Interesting statement. In contrast, I don't see how we can get along without SELV. My concept for SELV is that of ELV so protected from a higher voltage such that in the event of a fault, the SELV does not exceed the ELV limits. SELV can protect under single fault conditions. BUT, as I tried to explain, under some conditions, it can allow a single fault *to persist undetected*, until eventually a second, unrelated fault occurs which then results in a serious hazard. My concept for ELV is a voltage source that provides protection against electric shock by limitation of voltage. (ELV is not protected against an increase in voltage in the event of a fault.) Well, there is FELV (Functional ELV), which is protected by basic insulation only. ELV/SELV are important and extremely useful concepts because they allow access to low voltages such as those that become accessible during the interconnection of various units. As one example, consider the camcorder. SELV allows access to the battery charger terminals. Making these terminals inaccessible would increase the complexity and cost of a camcorder. For a single piece of equipment or a small collection very close together, SELV may be sufficient. But notice that if the double or reinforced insulation WERE to be faulty, the SELV would be S no longer. This is simply regarded as an event of acceptably low probability. Now consider the case of a video camera and recorder, connected via a cable carrying video on coax and power at SELV, some distance apart in a building. Contact between live mains and the video cable shield, due to an errant nail or screw, puts live mains on the shield, BUT the fault may remain undetected until someone tries to disconnect the cable or open one of the enclosures. With PELV, this does not happen: the grounding ensures that the protective device operates. I cannot imagine that you truly are not keen on the concept of SELV. I can imagine that you are not keen on the complexity of voltage limits for ELV/SELV. To this, I agree. Well, perhaps I have made it clearer now. My beef with SELV is the ban on grounding, whereas PELV which is grounded AND double/reinforced insulated is clearly safer for systems extended in space. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in 20031730.jaa05...@epgc196.sdd.hp.com) about 'Define Continuous DC Voltage', on Tue, 13 Nov 2001: Dc does not cause either tetanus or fibrillation. Tetanus is a disease caused by a bacillus. Muscles spasm is tetany. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Hi Gregg: There was also a very good (but short) article by Tektronix in the 70's called The Lethal Current. It concluded that currents between 100 mA and 3 Amps were more lethal that currents of more than 3 Amps because those high currents tended to 'restart' the heart. Hmm. Having been the manager of product safety at Tektronix in the '70's, I don't recall such an article. At least not by that name. Electric energy causes various injuries to the body depending on the magnitude of the energy. Only two of the injuries can lead to a fatality. The two injuries are fibrillation of the heart, and overheating of internal organs, especially the liver. Fibrillation is caused by ac current in the range of 50 mA to 500 mA (external connections) where the current pathway through the body includes the chest (and the heart). Above 500 mA, fibrillation is not a likely consequence. (And, I believe I am correct in asserting that dc cannot cause fibrillation.) Overheating of internal organs is a function of power dissipated in the body, where the body impedance can be taken as 1000 ohms. The power required depends on the time of contact. Electric utility linemen are subject to such injury. Consider 1 ampere through 1000 ohms is 1000 watts! (The electric chair kills by over-heating the internal organs, not by fibrillation.) So, Gregg's statement that there is both a lower and upper limit for fibrillation is correct (although I do not agree with Gregg's values). Best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Hi Chris: I'll attempt to answer the question as to the effect of ac and dc current on the body (the hazard). The discussion is in regard to three waveforms: 1) ac sinusoidal -- 50-60 Hz. 2) dc 3) dc interrupted (equal on and off times) up to 200 Hz. Each has a different effect on the body. For each waveform, the magnitudes of voltage and current at which the effect takes place are different. The body is most sensitive to ac, where the current reverses through the body. Such currents can cause both tetanus of various muscles, and fibrillation of the heart. Dc does not cause either tetanus or fibrillation. Dc with ripple or superimposed ac is still dc because the current does not reverse direction. From my reading of research papers, there is no significant effect on the body due to ac riding on a dc bias provided the current does not change direction. Interrupted dc (50% duty cycle, 0 mA off, up to 200 Hz) is surmised to have similar effect to that of ac. I believe that UL modeled this, and came to the conclusion that such interruption could cause fibrillation. (I don't believe any tests on animals or people were actually performed.) Hence, the limitation on voltage for such waveforms. Most of the research on live humans (grad students) was performed by Charles Dalziel, UC Berkeley, during the late 40's and early 50's. Dalziel published numerous papers on his tests, most in IRE and AIEE journals. Dalziel gave us the tetanus values for ac, and determined there was no tetanus for dc. Dalziel also gave us the effect of frequency on humans. During the 30's, 40's and 50's, UL also did some measurements on live humans (UL employees) to determine body impedance. Most recently, Beigelmeier (Vienna) has measured himself. His research is the basis for much of the data in IEC 60479, effects of current on the human body. Almost all other research was either on live (anesthesized) animals or on cadavers. When discussing waveforms that are beyond the research, we must identify the injury we wish to prevent. If we are considering 40 V dc which has an on/off period of 1 second, then the person can disconnect himself from the source during the 0.5-second off period. So, this would be the same as a steady-state 40 V dc source which is deemed non-hazardous. Best regards, Rich ps: Charles Dalziel is the inventor of the GFCI. Subject: RE: Define Continuous DC Voltage Date: Fri, 9 Nov 2001 16:10:29 -0500 From: Chris Maxwell chris.maxw...@nettest.com To: Ken Javor ken.ja...@emccompliance.com, Tania Grant taniagr...@msn.com, Doug McKean dmck...@corp.auspex.com, EMC-PSTC Discussion Group emc-p...@majordomo.ieee.org Sadly, I can't give that frequency; but I think I know the reasoning behind Eric's question... AC signals under 200Hz are especially dangerous to humans because AC currents really screw up our nervous system and cause death by heart attack at very low currents. It only takes milliamps of 60Hz AC current to kill a human being. On the other hand, people can withstand far more current from a DC source because it doesn't have the same effect on our nervous system. (Come on, who hasn't put a 9V battery on their tongue to test it out?) I think that this is the reasoning that the referenced standard uses to give two limits for AC and DC. My GUESS is that someone (who loved to torture living organisms) must have performed tests to figure out how DC current affected people (or monkeys, or rats... something). They then must have performed tests with different AC frequencies. Perhaps they even plotted a graph of hazardous voltage/current versus frequency. I would imagine that this is the type of data used by the IEC or any other safety organizationn to set hazardous voltage levels. Problem is...the standards don't give a graph or table of hazardous voltage vs. frequency, it just says DC and AC. Since we don't have access to the graph we really don't know what happens at ultra low frequencies. (Although I have a few rodents in my basement who are just asking to be test samples.) Of course, now there is the gray area of interpretation. (which keeps us all employed) For example, how would a safety engineer classify a 40V thermostat control signal (non current limited) with a five second hysteresis that prevents it from switching any faster than once every five seconds (0.2 Hz). Under normal conditions, this signal would switch once every couple of hours (0.00014Hz). Is this hazardous AC (after all it is 40V, and it does vary with time)? Or is it non-hazardous DC. Anybody want to tackle that question? It may help us to figure out Eric's initial problem. Remember to show your work...partial credit will be given :-) Just to show that I'm game... I'll take a stab. My opinion
Re: Define Continuous DC Voltage
Chris, check out IEC 479-1 (Effects of current on human beings and livestock). Real interesting reading - it mainly analyzes human body impedances (measurements taken on living humans and corpses) and discusses physiological effects of AC in range of 15-100 Hz and DC. In their study, it appears that 10 mA (in this AC range) is the point above which harmful physiological effects can occur and around 25 mA for DC. Above these limits, time of exposure will determine the threat of permanent and harmful effects. They do indicate that the physiological effects experiments were conducted on animals and were adapted to human beings. Human corpses were used in gathering human body impedance measurements from 25V to 5000 V. Barbecue anyone? -Scott Lemon Chris Maxwell wrote: My GUESS is that someone (who loved to torture living organisms) must have performed tests to figure out how DC current affected people (or monkeys, or rats... something). They then must have performed tests with different AC frequencies. Perhaps they even plotted a graph of hazardous voltage/current versus frequency. I would imagine that this is the type of data used by the IEC or any other safety organizationn to set hazardous voltage levels. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: Define Continuous DC Voltage
From my reading on the subject, EN 60950 has different Safety Extra-Low Voltage (SELV) limits for alternating current (AC) and direct current (DC) because the human body reacts to them differently. AC makes your muscles contract, so you tend to hang onto the source of the electric shock. DC makes you push away, removing contact, but you may fall or otherwise hurt yourself as you jerk away from the source of the shock. I have heard hams (amateur radio operators) tell of picking themselves off the floor, clear across the room, after accidently touching the plate supply of a tube radio. I found an article in Electronics magazine, published between 1940 and 1945 (I can't find the article right now), on a study that was done on let-go current. In this study the subjects (something like 100 young males) would grab a 1/4 wire with one hand, and put their other hand on a copper or brass plate. The experimenter would apply a voltage between the wire and the plate, giving the subject a shock. Then the subject would try to let go of the wire. If they couldn't, they could open the circuit just by lifting their hand from the plate. If the subject could let go of the wire, the experimenter would increase the voltage and they would try the experiment again. As I recall the experiments were done mainly at 50 and 60Hz, with some done at DC and low frequencies, and others up to 10kHz. The results of the study were that let-go current was lowest in the 40-100Hz range, and ranged from 15mA up to about 100mA. (I got the impression that some of the young men were trying to show how macho they were...) The let-go current increased as the frequency increased above 100Hz, or decreased below 40Hz. For DC the subjects had trouble trying to hold onto the wire, and instead of a shock they felt a heating effect. I have not seen any studies on how much AC superimposed on DC changes the let-go effect to a hang-on effect, and I don't plan to find out for myself if I don't have to... John Barnes Advisory Engineer Lexmark International --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: AW: Define Continuous DC Voltage
I read in !emc-pstc that Horst Haug innova...@t-online.de wrote (in nebbjgdeklhmddlcffinceancoaa.innova...@t-online.de) about 'AW: Define Continuous DC Voltage', on Sun, 11 Nov 2001: Enclosed are results of a SELV reliability test. The output inductance was shorted with no load and the ripple increased. In 1.2.13.4 (IEC60950) DC voltage is defined as a voltage with a peak to peak value less 10 % of the DC voltage. In the enclosed file you see the ripple with Peak 49,6 Vpmax and 42,4 Vpmin. The DC voltage is around 46 Vdc. 1. Now the argumentation could be: The voltage is not DC, because the ripple is above 10%. There is only AC or DC. Therefore, it has to be AC. The ripple is Vpeak max 49.6 V exceeding the defined max. peak of 42 V (2.2.2 of IEC60950). Therefore the output is not SELV any longer. This is a correct understanding of the definition of 'DC' used in several safety standards. 2. Another understanding is : The voltage is DC and AC. You have to split it into an AC part and a DC part. The DC part is 46 Vdc. This is a correct understanding of the *concept* of d.c. The AC part is 49,6 - 42,4 from peak to peak = 7,2 Vpeak to peak. Therefore it is SELV and pass. This is not a correct interpretation of the *safety standards*. It *is* a correct understanding of the *concept of a.c. This definition results in worse case into a 60 Vdc voltage overlayed with 42 V ripple resulting in Vpeak max of 81 V acceptable as SELV. If we agree with version 1, then it will be difficult to built up power supplies with nominal voltage of 48 Vdc. It is always easy to open a secondary cap or short a secondary inductance to increase the ripple above 10%. You are correct: 48 V is near enough to the upper limit of SELV to make preservation of conformity to the limit difficult under fault conditions. I have never been very keen on the concept of SELV, and I am glad to see that others are now recognizing the problems. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
AW: Define Continuous DC Voltage
Enclosed are results of a SELV reliability test. The output inductance was shorted with no load and the ripple increased. In 1.2.13.4 (IEC60950) DC voltage is defined as a voltage with a peak to peak value less 10 % of the DC voltage. In the enclosed file you see the ripple with Peak 49,6 Vpmax and 42,4 Vpmin. The DC voltage is around 46 Vdc. 1. Now the argumentation could be: The voltage is not DC, because the ripple is above 10%. There is only AC or DC. Therefore, it has to be AC. The ripple is Vpeak max 49.6 V exceeding the defined max. peak of 42 V (2.2.2 of IEC60950). Therefore the output is not SELV any longer. 2. Another understanding is : The voltage is DC and AC. You have to split it into an AC part and a DC part. The DC part is 46 Vdc. The AC part is 49,6 - 42,4 from peak to peak = 7,2 Vpeak to peak. Therefore it is SELV and pass. This definition results in worse case into a 60 Vdc voltage overlayed with 42 V ripple resulting in Vpeak max of 81 V acceptable as SELV. If we agree with version 1, then it will be difficult to built up power supplies with nominal voltage of 48 Vdc. It is always easy to open a secondary cap or short a secondary inductance to increase the ripple above 10%. Please let me know about your opinion. With best regards Horst -Ursprüngliche Nachricht- Von: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]Im Auftrag von Tania Grant Gesendet: Samstag, 10. November 2001 03:31 An: Ken Javor; Doug McKean; EMC-PSTC Discussion Group Betreff: Re: Define Continuous DC Voltage Thank you, Ken. You have given us all some food for thought;-- and just what did the standards writers have in mind when they said continuous? A ringing TNV voltage is treated differently from a continuous DC voltage. Is that as far as the definition goes? Did they have something else in mind? taniagr...@msn.com mailto:taniagr...@msn.com - Original Message - From: Ken Javor Sent: Friday, November 09, 2001 11:04 AM To: Tania Grant; Doug McKean; EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage I'm probably not providing any assistance, but what is the purpose of the categorization of continuous dc vs. that rate of change where it is not considered continuous anymore? I don't think it should be tied to ability to deliver power to a load, which is in agreement with what Ms. Grant is saying below. Pure dc provides power and no information. A signal uses power to transmit information. If I have a security alarm sensor on a window which always sends a low-level dc until the window is broken then if I look at the physical parameters I could say that low-level signal was dc because it could be on for years, but its PURPOSE is to transmit information which makes it a signal. Actually any single-sided digital transmission (meaning between 0 Volts and some Vcc) is dc in the classical sense because dc means direct current, as opposed to alternating current which changes direction. In the sense which people in this exchange have been using the terminology it refers to how much time rate of change is allowed. But this is where the question as to purpose comes in. If the issue is crosstalk, a low-level audio or video signal with lots of rate of change is a much more benign source than a 48 Vdc source from which lots of switched CURRENT is drawn. A dc POTENTIAL does NOT imply direct CURRENT unless CE limits have been applied to loads. So the question that has to be answered first is what is the purpose of the discrimination implied by the term continuous. -- From: Tania Grant taniagr...@msn.com To: Doug McKean dmck...@corp.auspex.com, EMC-PSTC Discussion Group emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage List-Post: emc-pstc@listserv.ieee.org Date: Thu, Nov 8, 2001, 9:47 PM Well now, Doug, how about the vast gray area in between? What if it is 1/50th of an amp? taniagr...@msn.com mailto:taniagr...@msn.com - Original Message - From: Doug McKean Sent: Thursday, November 08, 2001 7:39 PM To: EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage eric.lif...@ni.com wrote: So friends, how continuous must DC be to qualify as continuous DC? Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). That is basically the definition of rms anyway. To make the point with two ridiculous examples, (1) if by shorting a 5 volt digital signal to ground you measure 1/100th amps of rms current, then I wouldn't call it DC. (2) if by shorting a 5 volt digital signal to ground you measure 10 amps or rms current, then I'd most definitely call it DC. But that's just me and my 2 cents worth. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your
Re: Define Continuous DC Voltage
John, I read that, but I still see how it has anything to do specifically with the word hazardous. It appears that part of the standard in the poster's question is simply the only place in the standard where continuous is used in conjunction with DC voltage. I'm sure we could dissect this to no end. Perhaps the word continuous is used in the standard to reinforce the idea of uninterrupted. In other words, if we define a discontinuous DC voltage as being switched to zero or through zero (for example from a positive potential to a negative potential, then a continuous DC voltage is simply one that is not. - Doug --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
I read in !emc-pstc that robertj robe...@ma.ultranet.com wrote (in 01c1699e$2e8c7230$bef5accf@lrj006) about 'Define Continuous DC Voltage', on Fri, 9 Nov 2001: The closest example I have seen so far which touches (indirectly) on the subject is a proposal before the US TAG dealing with test pulses from a power supply operating in foldback. Remember this is a proposal and has not been through the review process. It is certainly far from adoption and you are unlikely to get away with it for the moment. It was developed with some consideration of cardiac sensitivity. It suggests pulses be permitted up to 120 volts of 20 milliseconds no less than 1 second apart or 200 milliseconds no less than 3 seconds apart. The idea is a recovery period reduces fibrillation sensitivity. It doesn't seem very likely that anyone would come in contact with the output voltage of a power supply operating in foldback. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: Define Continuous DC Voltage
Obviously if you can define your voltage as DC, you can get away with a much higher level (60 V) as SELV than if it is not (42.4 V peak). The reasons for the different levels are the shock potential. A varying voltage has a much greater potential to cause ventricular fibrillation than a DC voltage. Unfortunately the standards have not done a good job of defining the electrical difference between AC and DC. Obviously you cannot apply a 60 VDC voltage without a transient change with a peak of 60 Volts, and nothing is said about how often you can do it. Suggestions for improvements to the standards are welcome. The closest example I have seen so far which touches (indirectly) on the subject is a proposal before the US TAG dealing with test pulses from a power supply operating in foldback. Remember this is a proposal and has not been through the review process. It is certainly far from adoption and you are unlikely to get away with it for the moment. It was developed with some consideration of cardiac sensitivity. It suggests pulses be permitted up to 120 volts of 20 milliseconds no less than 1 second apart or 200 milliseconds no less than 3 seconds apart. The idea is a recovery period reduces fibrillation sensitivity. Bob -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Tania Grant Sent: Friday, November 09, 2001 9:31 PM To: Ken Javor; Doug McKean; EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage Thank you, Ken. You have given us all some food for thought;-- and just what did the standards writers have in mind when they said continuous? A ringing TNV voltage is treated differently from a continuous DC voltage. Is that as far as the definition goes? Did they have something else in mind? taniagr...@msn.com - Original Message - From: Ken Javor Sent: Friday, November 09, 2001 11:04 AM To: Tania Grant; Doug McKean; EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage I'm probably not providing any assistance, but what is the purpose of the categorization of continuous dc vs. that rate of change where it is not considered continuous anymore? I don't think it should be tied to ability to deliver power to a load, which is in agreement with what Ms. Grant is saying below. Pure dc provides power and no information. A signal uses power to transmit information. If I have a security alarm sensor on a window which always sends a low-level dc until the window is broken then if I look at the physical parameters I could say that low-level signal was dc because it could be on for years, but its PURPOSE is to transmit information which makes it a signal. Actually any single-sided digital transmission (meaning between 0 Volts and some Vcc) is dc in the classical sense because dc means direct current, as opposed to alternating current which changes direction. In the sense which people in this exchange have been using the terminology it refers to how much time rate of change is allowed. But this is where the question as to purpose comes in. If the issue is crosstalk, a low-level audio or video signal with lots of rate of change is a much more benign source than a 48 Vdc source from which lots of switched CURRENT is drawn. A dc POTENTIAL does NOT imply direct CURRENT unless CE limits have been applied to loads. So the question that has to be answered first is what is the purpose of the discrimination implied by the term continuous. -- From: Tania Grant taniagr...@msn.com To: Doug McKean dmck...@corp.auspex.com, EMC-PSTC Discussion Group emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage List-Post: emc-pstc@listserv.ieee.org Date: Thu, Nov 8, 2001, 9:47 PM Well now, Doug, how about the vast gray area in between? What if it is 1/50th of an amp? taniagr...@msn.com mailto:taniagr...@msn.com - Original Message - From: Doug McKean Sent: Thursday, November 08, 2001 7:39 PM To: EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage eric.lif...@ni.com wrote: So friends, how continuous must DC be to qualify as continuous DC? Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). That is basically the definition of rms anyway. To make the point with two ridiculous examples, (1) if by shorting a 5 volt digital signal to ground you measure 1/100th amps of rms current, then I wouldn't call it DC. (2) if by shorting a 5 volt digital signal to ground you measure 10 amps or rms current, then I'd most definitely call it DC. But that's just me and my 2 cents worth. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord
Re: Define Continuous DC Voltage
Thank you, Ken. You have given us all some food for thought;-- and just what did the standards writers have in mind when they said continuous? A ringing TNV voltage is treated differently from a continuous DC voltage. Is that as far as the definition goes? Did they have something else in mind? taniagr...@msn.com - Original Message - From: Ken Javor Sent: Friday, November 09, 2001 11:04 AM To: Tania Grant; Doug McKean; EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage I'm probably not providing any assistance, but what is the purpose of the categorization of continuous dc vs. that rate of change where it is not considered continuous anymore? I don't think it should be tied to ability to deliver power to a load, which is in agreement with what Ms. Grant is saying below. Pure dc provides power and no information. A signal uses power to transmit information. If I have a security alarm sensor on a window which always sends a low-level dc until the window is broken then if I look at the physical parameters I could say that low-level signal was dc because it could be on for years, but its PURPOSE is to transmit information which makes it a signal. Actually any single-sided digital transmission (meaning between 0 Volts and some Vcc) is dc in the classical sense because dc means direct current, as opposed to alternating current which changes direction. In the sense which people in this exchange have been using the terminology it refers to how much time rate of change is allowed. But this is where the question as to purpose comes in. If the issue is crosstalk, a low-level audio or video signal with lots of rate of change is a much more benign source than a 48 Vdc source from which lots of switched CURRENT is drawn. A dc POTENTIAL does NOT imply direct CURRENT unless CE limits have been applied to loads. So the question that has to be answered first is what is the purpose of the discrimination implied by the term continuous. -- From: Tania Grant taniagr...@msn.com To: Doug McKean dmck...@corp.auspex.com, EMC-PSTC Discussion Group emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage List-Post: emc-pstc@listserv.ieee.org Date: Thu, Nov 8, 2001, 9:47 PM Well now, Doug, how about the vast gray area in between? What if it is 1/50th of an amp? taniagr...@msn.com mailto:taniagr...@msn.com - Original Message - From: Doug McKean Sent: Thursday, November 08, 2001 7:39 PM To: EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage eric.lif...@ni.com wrote: So friends, how continuous must DC be to qualify as continuous DC? Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). That is basically the definition of rms anyway. To make the point with two ridiculous examples, (1) if by shorting a 5 volt digital signal to ground you measure 1/100th amps of rms current, then I wouldn't call it DC. (2) if by shorting a 5 volt digital signal to ground you measure 10 amps or rms current, then I'd most definitely call it DC. But that's just me and my 2 cents worth. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
I read in !emc-pstc that eric.lif...@ni.com wrote (in of5431d5be.3bcd92cd-on86256aff.0061d...@natinst.com) about 'Define Continuous DC Voltage', on Fri, 9 Nov 2001: John Woodgate commented: [...] A digital signal that has one value at 0 V to ground and the other value at voltage V consists of a d.c. voltage of amplitude V/2 plus an a.c. voltage of (double) amplitude V/2. The frequency of the a.c. is irrelevant. [...] Per IEC 60950:1999, also in UL 1950:1995 (but not in '1010 or UL 31x1), D.C. Voltage is defined as: The average value of a voltage (as measured by a moving coil meter) having a peak-to-peak ripple not exceeding 10% of the average value. Note - Where peak-to-peak ripple exceeds 10% of the average value, the requirements related to peak voltage are applicable. I could not find the V/2 clause in 950. Perhaps its the TNV section of UL 1950:1995, clause 6.2.1.1, though it differs in that the divisor is not 2, but what I'd call a reference voltage, 42.4 V and others. Frequency here is limited to 100 Hz and below. It also repeats the 10% ripple criteria in Table 8. It isn't there, simply because 60950 is concerned with safety and not with defining what 'd.c.' is as a concept, which is what my text is about. The first part of the 60950 text is, however, entirely consistent with my text. Given a moving-coil meter with a long enough averaging time (much longer than the lowest frequency alternating voltage present), the meter will read V/2. The second part is not about the concept of 'd.c.', but entirely about how to treat, for safety purposes, a voltage that is part d.c. and part a.c., when the a.c. part exceeds 10%. It seems unclear (for us '1010 users) as to how continuous in time a DC voltage from 42.4 V DC Peak to 60 V DC Peak must be to avoid falling into the AC Peak limits, in an application that switches circuits on/off either randomly or periodically. It seems clear that the authors of 60950 did not take into account the case that troubles you. But, in Europe anyway, if your product is a '61010' product, you don't have to apply ANY of the provisions of 60950. Perhaps a simple voltage/frequency table derived from the Annex P leakage current model would allow our customers to use the full DC Voltage rating for sub 48 Hz switching rates, and specify a sliding scale of maximum rated voltage as the highest switching frequency goes up. That should be proposed to the new IEC TC108 as an improvement to IEC60950. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
RE: Define Continuous DC Voltage
Sadly, I can't give that frequency; but I think I know the reasoning behind Eric's question... AC signals under 200Hz are especially dangerous to humans because AC currents really screw up our nervous system and cause death by heart attack at very low currents. It only takes milliamps of 60Hz AC current to kill a human being. On the other hand, people can withstand far more current from a DC source because it doesn't have the same effect on our nervous system. (Come on, who hasn't put a 9V battery on their tongue to test it out?) I think that this is the reasoning that the referenced standard uses to give two limits for AC and DC. My GUESS is that someone (who loved to torture living organisms) must have performed tests to figure out how DC current affected people (or monkeys, or rats... something). They then must have performed tests with different AC frequencies. Perhaps they even plotted a graph of hazardous voltage/current versus frequency. I would imagine that this is the type of data used by the IEC or any other safety organizationn to set hazardous voltage levels. Problem is...the standards don't give a graph or table of hazardous voltage vs. frequency, it just says DC and AC. Since we don't have access to the graph we really don't know what happens at ultra low frequencies. (Although I have a few rodents in my basement who are just asking to be test samples.) Of course, now there is the gray area of interpretation. (which keeps us all employed) For example, how would a safety engineer classify a 40V thermostat control signal (non current limited) with a five second hysteresis that prevents it from switching any faster than once every five seconds (0.2 Hz). Under normal conditions, this signal would switch once every couple of hours (0.00014Hz). Is this hazardous AC (after all it is 40V, and it does vary with time)? Or is it non-hazardous DC. Anybody want to tackle that question? It may help us to figure out Eric's initial problem. Remember to show your work...partial credit will be given :-) Just to show that I'm game... I'll take a stab. My opinion is that, if it can be proven that this signal will switch at a frequency no higher than 0.2 Hz under all normal and single fault conditions; then you have a non-hazardous DC signal. (Note that I'm not saying 0.2 Hz is the cutoff, it's probably higher.) OK... I've hung it out there. Either agree with it or refute it. Either way, we'll all learn something. Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | -Original Message- From: Ken Javor [SMTP:ken.ja...@emccompliance.com] Sent: Friday, November 09, 2001 1:22 PM To: Tania Grant; Doug McKean; EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage I'm probably not providing any assistance, but what is the purpose of the categorization of continuous dc vs. that rate of change where it is not considered continuous anymore? I don't think it should be tied to ability to deliver power to a load, which is in agreement with what Ms. Grant is saying below. Pure dc provides power and no information. A signal uses power to transmit information. If I have a security alarm sensor on a window which always sends a low-level dc until the window is broken then if I look at the physical parameters I could say that low-level signal was dc because it could be on for years, but its PURPOSE is to transmit information which makes it a signal. Actually any single-sided digital transmission (meaning between 0 Volts and some Vcc) is dc in the classical sense because dc means direct current, as opposed to alternating current which changes direction. In the sense which people in this exchange have been using the terminology it refers to how much time rate of change is allowed. But this is where the question as to purpose comes in. If the issue is crosstalk, a low-level audio or video signal with lots of rate of change is a much more benign source than a 48 Vdc source from which lots of switched CURRENT is drawn. A dc POTENTIAL does NOT imply direct CURRENT unless CE limits have been applied to loads. So the question that has to be answered first is what is the purpose of the discrimination implied by the term continuous. -- From: Tania Grant taniagr...@msn.com To: Doug McKean dmck...@corp.auspex.com, EMC-PSTC Discussion Group emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage Date: Thu, Nov 8, 2001, 9:47 PM Well now, Doug, how about the vast gray area in between? What if it is 1/50th of an amp? taniagr...@msn.com mailto:taniagr...@msn.com - Original Message
Re: Define Continuous DC Voltage
Doug et al, I think John realized that I was led down the path to UL 1310 and it's strange clause (continuous) in an attempt to quantify how/when a DC voltage becomes regarded to be an AC voltage in terms of hazard. I wasn't clear on that. Best Regards, Eric Lifsey Doug McKean dmck...@corp.auspex.coTo: EMC-PSTC Discussion Group m emc-p...@majordomo.ieee.org Sent by: cc: owner-emc-pstc@majordomSubject: Re: Define Continuous DC Voltage o.ieee.org 11/09/2001 12:26 PM Please respond to Doug McKean Well, to follow John's and Tania's comments ... For John, there wasn't any mention of hazardous in the original question. Only what would qualify as continuous DC. So, IMO, it doesn't matter what the frequency is as I stated with regards to an rms nor the level with regard to hazardous. The rms converts any signal dc or ac to a continuously delivered power to a load in terms of real power. Which brings me to Tania's question as in, whatever level you wish to consider. If it is 1/50th, then so be it. I thought it was an interesting question when I started considering heating effects with say fine pitch traces and such. Anywho, just my two cents ... Regards, Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
I read in !emc-pstc that Doug McKean dmck...@corp.auspex.com wrote (in 000a01c1694c$1bc34ea0$3e3e3...@corp.auspex.com) about 'Define Continuous DC Voltage', on Fri, 9 Nov 2001: For John, there wasn't any mention of hazardous in the original question. Only what would qualify as continuous DC. What do you make of this extract from the original post, if it's not about hazardous voltages? QUOTE I consulted two UL standards: 508C and 3121-1 (and it's kin 3101/3111-1, all based on IEC 61010-1), both led me (by reference) to UL 1310 Class 2 Power Units. UL 1310 has a clause (14.2.2) which indicates that a DC interrupted at a rate of 200 Hz or less is limited to 24.8 V peak. In the same clause it mentions a continuous DC voltage of 60 V DC is permissible. UNQUOTE -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Doug McKean commented: [...] Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). [...] The device in question can drive several milliamps on each channel, which I believe is a healthy shock. As a limited energy source it is unlikely to be a fire hazard. Since the model of the body is roughly 2,000 Ohms, that's a potential for up to 30 mA at 60 V DC and is probably rather painful. (There was a very good thread on fibrillation and other biological aspects of current about four [?] years ago on this list.) See Annex D of '950 for the leakage current model, which is also influenced by frequency. John Woodgate commented: [...] A digital signal that has one value at 0 V to ground and the other value at voltage V consists of a d.c. voltage of amplitude V/2 plus an a.c. voltage of (double) amplitude V/2. The frequency of the a.c. is irrelevant. [...] Per IEC 60950:1999, also in UL 1950:1995 (but not in '1010 or UL 31x1), D.C. Voltage is defined as: The average value of a voltage (as measured by a moving coil meter) having a peak-to-peak ripple not exceeding 10% of the average value. Note - Where peak-to-peak ripple exceeds 10% of the average value, the requirements related to peak voltage are applicable. I could not find the V/2 clause in 950. Perhaps its the TNV section of UL 1950:1995, clause 6.2.1.1, though it differs in that the divisor is not 2, but what I'd call a reference voltage, 42.4 V and others. Frequency here is limited to 100 Hz and below. It also repeats the 10% ripple criteria in Table 8. It seems unclear (for us '1010 users) as to how continuous in time a DC voltage from 42.4 V DC Peak to 60 V DC Peak must be to avoid falling into the AC Peak limits, in an application that switches circuits on/off either randomly or periodically. Perhaps a simple voltage/frequency table derived from the Annex P leakage current model would allow our customers to use the full DC Voltage rating for sub 48 Hz switching rates, and specify a sliding scale of maximum rated voltage as the highest switching frequency goes up. Thanks and Best Regards, Eric Lifsey Compliance Manager National Instruments --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Well, to follow John's and Tania's comments ... For John, there wasn't any mention of hazardous in the original question. Only what would qualify as continuous DC. So, IMO, it doesn't matter what the frequency is as I stated with regards to an rms nor the level with regard to hazardous. The rms converts any signal dc or ac to a continuously delivered power to a load in terms of real power. Which brings me to Tania's question as in, whatever level you wish to consider. If it is 1/50th, then so be it. I thought it was an interesting question when I started considering heating effects with say fine pitch traces and such. Anywho, just my two cents ... Regards, Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
I'm probably not providing any assistance, but what is the purpose of the categorization of continuous dc vs. that rate of change where it is not considered continuous anymore? I don't think it should be tied to ability to deliver power to a load, which is in agreement with what Ms. Grant is saying below. Pure dc provides power and no information. A signal uses power to transmit information. If I have a security alarm sensor on a window which always sends a low-level dc until the window is broken then if I look at the physical parameters I could say that low-level signal was dc because it could be on for years, but its PURPOSE is to transmit information which makes it a signal. Actually any single-sided digital transmission (meaning between 0 Volts and some Vcc) is dc in the classical sense because dc means direct current, as opposed to alternating current which changes direction. In the sense which people in this exchange have been using the terminology it refers to how much time rate of change is allowed. But this is where the question as to purpose comes in. If the issue is crosstalk, a low-level audio or video signal with lots of rate of change is a much more benign source than a 48 Vdc source from which lots of switched CURRENT is drawn. A dc POTENTIAL does NOT imply direct CURRENT unless CE limits have been applied to loads. So the question that has to be answered first is what is the purpose of the discrimination implied by the term continuous. -- From: Tania Grant taniagr...@msn.com To: Doug McKean dmck...@corp.auspex.com, EMC-PSTC Discussion Group emc-p...@majordomo.ieee.org Subject: Re: Define Continuous DC Voltage List-Post: emc-pstc@listserv.ieee.org Date: Thu, Nov 8, 2001, 9:47 PM Well now, Doug, how about the vast gray area in between? What if it is 1/50th of an amp? taniagr...@msn.com mailto:taniagr...@msn.com - Original Message - From: Doug McKean Sent: Thursday, November 08, 2001 7:39 PM To: EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage eric.lif...@ni.com wrote: So friends, how continuous must DC be to qualify as continuous DC? Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). That is basically the definition of rms anyway. To make the point with two ridiculous examples, (1) if by shorting a 5 volt digital signal to ground you measure 1/100th amps of rms current, then I wouldn't call it DC. (2) if by shorting a 5 volt digital signal to ground you measure 10 amps or rms current, then I'd most definitely call it DC. But that's just me and my 2 cents worth. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
I read in !emc-pstc that Doug McKean dmck...@corp.auspex.com wrote (in 000b01c1689b$3fc85e00$3e3e3...@corp.auspex.com) about 'Define Continuous DC Voltage', on Thu, 8 Nov 2001: So friends, how continuous must DC be to qualify as continuous DC? Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). That is basically the definition of rms anyway. To make the point with two ridiculous examples, (1) if by shorting a 5 volt digital signal to ground you measure 1/100th amps of rms current, then I wouldn't call it DC. (2) if by shorting a 5 volt digital signal to ground you measure 10 amps or rms current, then I'd most definitely call it DC. But that, while probably important, is not about 'continuity'. In any case, IEC/EN60950 already defines what voltages and currents are hazardous in various ways. A digital signal that has one value at 0 V to ground and the other value at voltage V consists of a d.c. voltage of amplitude V/2 plus an a.c. voltage of (double) amplitude V/2. The frequency of the a.c. is irrelevant. I think the cited standards were written while this concept was not loaded into memory. (;-) -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Well now, Doug, how about the vast gray area in between? What if it is 1/50th of an amp? taniagr...@msn.com - Original Message - From: Doug McKean Sent: Thursday, November 08, 2001 7:39 PM To: EMC-PSTC Discussion Group Subject: Re: Define Continuous DC Voltage eric.lif...@ni.com wrote: So friends, how continuous must DC be to qualify as continuous DC? Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). That is basically the definition of rms anyway. To make the point with two ridiculous examples, (1) if by shorting a 5 volt digital signal to ground you measure 1/100th amps of rms current, then I wouldn't call it DC. (2) if by shorting a 5 volt digital signal to ground you measure 10 amps or rms current, then I'd most definitely call it DC. But that's just me and my 2 cents worth. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
eric.lif...@ni.com wrote: So friends, how continuous must DC be to qualify as continuous DC? Personally, I'd say when the source can deliver some sufficient level of real power (rms level of power). That is basically the definition of rms anyway. To make the point with two ridiculous examples, (1) if by shorting a 5 volt digital signal to ground you measure 1/100th amps of rms current, then I wouldn't call it DC. (2) if by shorting a 5 volt digital signal to ground you measure 10 amps or rms current, then I'd most definitely call it DC. But that's just me and my 2 cents worth. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Re: Define Continuous DC Voltage
Us OLD guys used to think that digital was two levels of voltage - back then +5VDC and 0VDC. Thus DC could also mean Digital Computers. Way back then, the things did run relatively slow compared to these days so the AC signal you think of was only the step function of getting from one level to the next. In fact, we used to do that with switches on the front panel - manual clocks. These days, DC step functions happen faster than the settling time, leading to the appearance of AC looking signals. - Bill At 05:53 PM 11/07/2001 , eric.lif...@ni.com wrote: A question was posed as to when a digital I/O signal can be treated as a DC voltage source. My reaction is it must be treated as a AC signal. However, it could be operated such that the output changes state rather slowly. (This is a simple programmable I/O port for most any use.) But, the concept and some digging led me to another question. I consulted two UL standards: 508C and 3121-1 (and it's kin 3101/3111-1, all based on IEC 61010-1), both led me (by reference) to UL 1310 Class 2 Power Units. UL 1310 has a clause (14.2.2) which indicates that a DC interrupted at a rate of 200 Hz or less is limited to 24.8 V peak. In the same clause it mentions a continuous DC voltage of 60 V DC is permissible. To my knowledge, a rate of 200 Hz or less is explicitly saying that any interruption in power, even to shut it down on occasion, invokes the 28.4 V DC limit. (Silly interpretation, but that's what it says.) So friends, how continuous must DC be to qualify as continuous DC? Best Regards, Eric Lifsey Compliance Manager National Instruments --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. - British Prime Minister Tony Blair pointed to the victims of the Sept. 11 attacks on the World Trade Center and the Pentagon, and said the Taliban regime had no moral inhibition on slaughtering innocent people. There is no compromise possible with such people, no meeting of minds, no point of understanding with such terror, he said. There is just a choice: Defeat it or be defeated by it and defeat it we must. Whatever the dangers of the action we take, the dangers of inaction are far, far greater, he said. Bill Owsley, ows...@cisco.com 919) 392-8341 Compliance Engineer Cisco Systems 7025 Kit Creek Road POB 14987 RTP. NC. 27709 --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
Define Continuous DC Voltage
A question was posed as to when a digital I/O signal can be treated as a DC voltage source. My reaction is it must be treated as a AC signal. However, it could be operated such that the output changes state rather slowly. (This is a simple programmable I/O port for most any use.) But, the concept and some digging led me to another question. I consulted two UL standards: 508C and 3121-1 (and it's kin 3101/3111-1, all based on IEC 61010-1), both led me (by reference) to UL 1310 Class 2 Power Units. UL 1310 has a clause (14.2.2) which indicates that a DC interrupted at a rate of 200 Hz or less is limited to 24.8 V peak. In the same clause it mentions a continuous DC voltage of 60 V DC is permissible. To my knowledge, a rate of 200 Hz or less is explicitly saying that any interruption in power, even to shut it down on occasion, invokes the 28.4 V DC limit. (Silly interpretation, but that's what it says.) So friends, how continuous must DC be to qualify as continuous DC? Best Regards, Eric Lifsey Compliance Manager National Instruments --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
