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:
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.
