re: Symbols vs. text - was EN61010-1, Symbol 14
Hi Rich, First, do we have clear, unambiguous definitions for our safety symbols? Based on the very short definitions in 417, I think not. I believe we need much more work on the definitions. As you know, standards are not static things set in stone. If you think that IEC 60417 needs to be changed to improve understanding then join the relevant committee and make a proposal. No proposal, no change. Even if everyone on this exploder list were to express their agreement with your sentiment, and even if they were to subsequently agree exactly what the change should be, then that would count for nothing unless someone took an action to propose and champion the change. That's just a fact of life in any standards making forum that I've been associated with, and is certainly true in the IEC. Products should be designed so that no safety symbols/words are required (at least for the user/operator). A very laudable viewpoint and one that is easily achievable in the examples you provided. However, with certain products there has to be a residual risk or the product simply will not function. Show me an electric chainsaw that has no residual risk and I'll show you a piece of worthless junk. Nearer to home, photocopiers and certain laser printers use a hot fuser to melt the toner on/into the paper, sometimes the paper (or acetate, especially if the user uses what's to hand rather than ordering the correct type) gets stuck in/on the fuser (depending whether it uses radiant heat or hot roll technology)and the operator needs to remove it. The manufacturer has to select a temperature and technology that it is not so hot that it burns the end user - but equally is not so cold that it takes ages for the equipment to cool down and heat up to working temperature again. This could be done with a temperature sensor that does not operate a solenoid to permit human access 'till the temperature is low enough if money were no object, but more often manufactures do not go this far and instead they simply fit a temperature hazard symbol and put suitable instructions in the user manual. You ask So what do we do as regards written words? My response is design the product so that no words or symbols are needed insofar as safety is concerned. And my reply to you is that safety engineers should aim to eliminate or minimise hazards to the maximum extent practicable and safety warnings should only be used as a last resort. However, sometimes the last resort is the only resort left and under such circumstances suitable warnings (whether text or symbols) will need to be used. If a safety standard were ever to mandate that safety warnings could never be used to protect casual users then I suggest to you that such a standard would not be used by a large number of companies. Of course, it is also perfectly reasonable for a company to decide that ITS products will always be designed without recourse to user safety warnings, no matter how high the product cost. Perhaps that company is convinced that the best engineering risk reduction solutions are more 'idiot proof' than the best procedural risk reduction procedures. Perhaps that company concluded that, when awarding damages, the legal system does not always seem to adequately take into account whether the action leading to an injury was as a result of an act made by a person acting in a reasonable or reckless manner. Perhaps that company is concerned about the potential product recall costs and/or loss of 'good name' resulting from a lost law suit or bad press. Equally, another company could perform a similar risk management analysis and come to a different conclusion because its circumstances were different. All the best, Richard Hughes. Safety Answer Ltd. 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Symbols vs. text - was EN61010-1, Symbol 14
Hi Richard: You said We in the product safety industry must be very careful that we use symbols in strict accordance with their definitions. No issue with you there. However, the paper states that some of these misuses were perpetrated by people not even connected with electrical engineering, let alone safety. Indeed. We need to keep such people from learning about our safety symbols (except when we use them in the proper venue and context). :-) This brings me to another of your statements The fact of misuse of symbols dilutes the meaning of the symbol. The more the misuse, the less valuable the symbol is for safety purposes. Perhaps this is true, let's assume it is for the moment. What then are the options available to us? Either we have to find a way of policing the use safety symbols or we have to face the possibility that every symbol described in IEC 60417 could become unusable due to misuse. Any suggestions on how to police (internationally, of course) the incorrect use of IEC and ISO symbols? We need to first make sure our house is in order. First, do we have clear, unambiguous definitions for our safety symbols? Based on the very short definitions in 417, I think not. I believe we need much more work on the definitions. Second, we need to make sure we only use the symbols in accordance with the definition. We can police ourselves through our traditional third-party safety certification of products. So what do we do as regards written words? We look at the context in which the word is used. If I were to pronounce that an object is cool then the chances are that I would mean that it is below room temperature - but if my daughter were to pronounce an object cool then the chances are that it would be the latest 'in thing'. Confusing? In theory maybe, in practice not really. Of course, the standards for word definitions (which, for the sake of simplicity, I'll call dictionaries) do describe multiple common uses of individual words (including examples of their contextual usage, if they're any good). The preceding is a very good statement of the problem of multiple definitions for both words and symbols. Let's back up a step and ask the purpose of the symbol (or even the set of words). I submit that the purpose is to invoke an action on the part of the reader. If the symbol/words is in regard of safety, then I submit that the action invoked is because of lack of a suitable safeguard. Products should be designed so that no safety symbols/words are required (at least for the user/operator). If you look at your monitor, keyboard, and computer, you probably will see no symbols or words relating to safety. So, products CAN be designed without the need for safety symbols. You ask So what do we do as regards written words? My response is design the product so that no words or symbols are needed insofar as safety is concerned. 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Symbols vs. text - was EN61010-1, Symbol 14
Rich, Thank you for explaining that words were made from letters and sentences were made from a mixture of words (and letters by the way). It's simply amazing how informative these exchanges can be! You said We in the product safety industry must be very careful that we use symbols in strict accordance with their definitions. No issue with you there. However, the paper states that some of these misuses were perpetrated by people not even connected with electrical engineering, let alone safety. This brings me to another of your statements The fact of misuse of symbols dilutes the meaning of the symbol. The more the misuse, the less valuable the symbol is for safety purposes. Perhaps this is true, let's assume it is for the moment. What then are the options available to us? Either we have to find a way of policing the use safety symbols or we have to face the possibility that every symbol described in IEC 60417 could become unusable due to misuse. Any suggestions on how to police (internationally, of course) the incorrect use of IEC and ISO symbols? So what do we do as regards written words? We look at the context in which the word is used. If I were to pronounce that an object is cool then the chances are that I would mean that it is below room temperature - but if my daughter were to pronounce an object cool then the chances are that it would be the latest 'in thing'. Confusing? In theory maybe, in practice not really. Of course, the standards for word definitions (which, for the sake of simplicity, I'll call dictionaries) do describe multiple common uses of individual words (including examples of their contextual usage, if they're any good). Pete, I recognise that you favour combining symbols with language markings until there has been considerable training as to the correct meaning of what each symbol means. You do not say who should perform this training nor what the acceptance criteria should be. Of course, the manufacturer could explain in their instructions for the user what the various symbols mean - but of course you could reply that not everyone reads the manuals and manuals get lost and are not always passed on to second users: all of which is in part true. It is also true that many of us live in multi-cultural societies. In England not everyone reads or speaks British English and in the USA not everyone reads or speaks American English, so simply providing textural warnings in English (of either sort) in these two countries will also not cover 100% of the population. If your argument is that symbols are no use without warning text to explain their meaning then having a symbol with an explanatory in a language you don't understand is no use either. All, So what answer do we have? Perhaps we are looking in the wrong place. After all, when the folks in SiFi movies get transported to some strange alien planet and come across a black and metallic device in a cavern that is covered with flashing lights, it never seems to take them long to work out which buttons to press in order to get back home again. Perhaps all we really need then is a device that can instantly analyse our DNA left on the appropriate button, predict the range of possible languages we are likely to understand, and then project this information to us via some suitable imaging device. Of course, this would really just be a stop-gap until we can work out how to transmit the information telepathically and do without the visual imaging device and perhaps the need for a universal translator. Until the above utopian dream comes about we are faced with living in an imperfect world. Neither symbols nor text based information will ever get through to 100% of the population. Convert everyone on earth to speak a single language? Well, why not, every Klingon speaks just one language - right? I'm sure I'll be out-voted on this one, but give me the proper British version of English rather than that upstart American version any day! Over and out, Richard Hughes. 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: path-loss equation
This is a multi-part message in MIME format. Hello, The factor of 37 came as a constant when the numbers were plugged in appropriate units. But bascially it is Free Space Path Loss Equation. The path loss varies quadratically with distance hence a factor of 20logdistance. To account for loss due to reflections either take as 40 log distance but then the factor 37 might change. Or the best way I go about doing is to take calculate FSL and then add FAde margin 30dB or whatever to account for reflection, fading and other phenomenon. Refer Application Note of Intersil AN9804 tutorial on Link Budget Analysis for the calculations. Also there is a Tech Note by MAxim good one on this calculation. Hope this helps. HImanshu Arora PhD Student, Mixed Signal and RF IC Design, Duke University. Durham, NC. --- Ken Javor ken.ja...@emccompliance.com wrote: If you are calculating attenuation over distance, I don't see where frequency plays a role, unless you are at a frequency where the atmosphere attenuates the transmission, as it would at the frequency you picked. In general, I would use the basic range equation: Pd = Pt G/(4 pi r^2). If there are secondary reflections, the reflection point can be treated as a new source of square-law loss transmissions, resulting in a fourth-law loss overall. This is how a radar works. My opinion is that the equation you found is for some special case, derivable from the above considerations. Ken Javor From: George Stults george.stu...@watchguard.com Reply-To: George Stults george.stu...@watchguard.com Date: Thu, 10 Apr 2003 08:23:59 -0700 To: emc-p...@majordomo.ieee.org Subject: path-loss equation Hello Group, I came across an equation for radiated signal path-loss (attenuation). I¹d like to check my understanding of its meaning. The equation is Attenuation = 37 + 20 log (F MHz) + 20 log (D miles). So for instance, If I wanted to know the distance for a radiated signal (2450 MHz) to be attenuated by 100db, the calculation would be [100 37 20 log (2450)] / 20 = log (D miles) and the answer in miles would be 0.5765 milesŠ or 3044 feet. My assumption is that this equation gives an answer for line-of-sight (1/R^2) type of loss.I¹d like to estimate loss for a cluttered environment that approximates 1/R^3 or 1/R^4. My question is, how could this equation be modified for that purpose, or is there some other standard equation to estimate loss at a given frequency in varying environments, either in meters or feet etc. I have tried a few ideas, but numeracy fails me on this occasion. Thanks in Advance. George Stults WatchGuard Technologies Inc. __ Do you Yahoo!? The New Yahoo! Search - Faster. Easier. Bingo http://search.yahoo.com Title: Re: path-loss equation Hello, The factor of 37 came as a constant when the numbers were plugged in appropriate units. But bascially it is Free Space Path Loss Equation. The path loss varies quadratically with distance hence a factor of 20logdistance. To account for loss due to reflections either take as 40 log distance but then the factor 37 might change. Or the best way I go about doing is to take calculate FSL and then add FAde margin 30dB or whatever to account for reflection, fading and other phenomenon. Refer Application Note of Intersil AN9804 tutorial on Link Budget Analysis for the calculations. Also there is a Tech Note by MAxim good one on this calculation. Hope this helps. HImanshu Arora PhD Student, Mixed Signal and RF IC Design, Duke University. Durham, NC. --- Ken Javor ken.ja...@emccompliance.com wrote: If you are calculating attenuation over distance, I don't see where frequency plays a role, unless you are at a frequency where the atmosphere attenuates the transmission, as it would at the frequency you picked. In general, I would use the basic range equation: Pd = Pt G/(4 pi r^2). If there are secondary reflections, the reflection point can be treated as a new source of square-law loss transmissions, resulting in a fourth-law loss overall. This is how a radar works. My opinion is that the equation you found is for some special case, derivable from the above considerations. Ken Javor From: George Stults george.stu...@watchguard.com Reply-To: George Stults george.stu...@watchguard.com Date: Thu, 10 Apr 2003 08:23:59 -0700 To: emc-p...@majordomo.ieee.org Subject: path-loss equation Hello Group, I came across an equation for radiated signal path-loss (attenuation). I¹d like to check my understanding of its meaning. The equation is Attenuation = 37 + 20 log (F MHz) + 20 log (D miles). So for instance, If I wanted to know the distance for a radiated signal (2450 MHz) to be attenuated by 100db, the
Re: Lightning coordination in K.20 (2000) versus GR-1089
In a message dated 4/17/2003, you write: As an FYI, we see very few instances of damage on our carrier class products due to lightning events. As such I doubt the coordination issue is really that significant. Hi Jim: Thanks for your detailed discussion of the coordination problem. I share the concerns you expressed, particularly your general discomfort with the surge tolerance of PTC devices. I should also mention that my own experience is that GR-1089 compliant products rarely have lightning failures in the field. I have seen some cases where the *voltage* of real world longitudinal lightning surges exceeded what GR-1089 tests for, due to nonfunctional primary protectors. GR-1089 makes no attempt to treat this field condition as a Level 1 test, but experience has taught me that it must be considered. On the other hand, I have not seen any significant incidence of cases where the short circuit *current* was enough to damage a GR-1089 compliant design. Fuses that can handle a 10x1000 uS, 100 amp surge almost never fail in the field. This suggests to me that the coordination requirement in the new K.20 is excessive, and that the coordination requirement in GR-1089 is probably more closely aligned with actual field conditions. GR-1089 does not require the primary protector to operate if the secondary protector can handle 10x1000 uS 100 amp surges. I wonder whether there is any room for the authors of K.20 to consider lowering the amount of short circuit current that the secondary protection must be able to survive in order to waive the requirement that the primary protector must operate. The present K.20 level of 1000 amps is extraordinary. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 j...@randolph-telecom.com http://www.randolph-telecom.com
