UL1662 DC Power Cable
I have a power cord sample from a vendor that I would like to use for 48VDC power distribution in a computer system. It's super flexible and ideal for my application. Does UL1662 cable meet the safety requirements for this type of application for UL/CSA/TUV? Thanks, Max Kelson mkel...@es.com
Re: Need EMC Help With Video Card
Tony, Thanks for the great ideas! %> %>Hi, %>One way to do this would be to line the gap with decoupling caps %>in the vicinity where the traces cross, on either side of the gap. The %>values of the caps would be chosen so that they self-resonate %>(due to self AND via series inductance) in the problem frequency range. %>But 189 MHz is getting up there in frequency. Assuming 8 nH (3 nH %>per via and 2 nH cap self inductance) a decoupling cap value 100pF is %>in the ballpark. I hadn't given any thought to this problem, but now that you mention it, I have found a spot in Intel's P6 application notes where they recommend doing the same thing. The problem of course is in trying to get them at the resonant frequency and there is a chance that the next turn of the card (a major change) will have a problem at a different harmonic. Still, it's worth a try. %> %>I don't really like that approach. Instead, I wonder why the route is %>allowing traces to jump the gap between analog and digital power. %>I would think that most of the shared circuitry between analog and digital %>power is within the DAC itself and that if the power planes are well placed %>and of the proper shape, there isn't much external route on the board that %>needs to intermingle between the two power areas, especially not a clock %>signal. We have designed the board so that our DAC power plane doesn't have this problem. I learned that the hard way! However, the other island involved is a 3.3V island in the 5V power plane. %> %>Even if power and ground are solid planes, I don't like that layers 1 %>and 8 do not have a return layer adjacent to them. Again, loop area is %>greater than the optimum value unless you use significant return route %>on the same layer adjacent to to signal route for any critical signal on %>these %>top and bottom layers. If more power and ground layers are not an option, %>I would rather see the signal layer count DECREASE by two layers %>using a 6 layer board with your stackup or DECREASE by four layers %>with the power and ground layers in the middle to take advantage %>of better distributed capacitance board decoupling. I agree completely. I have sent a note out saying that the only good solution is to get the number of signal layers down to four and to add two additional ground planes. %> %>You will get better high frequency decoupling if power and ground %>are adjacent in the stackup. This is due to the distributed capacitance %>created by the adjacent planes due to the more closely spaced planes %>(capacitor "plates"). With the number of signal layers you %>are using, you would exacerbate the problems of adjacent layer %>returns if you went to this type of structure. So considering the number %>of power and ground planes vs. signal layers you have, your current %>stackup with its deficiencies are your most logical option. Again, for this %>many signal layers, I would like to see one more power and one more %>ground layer with the following stackup. %> %> S %> S %> G %> P %> S %> S %> P %> G %> S %> S I wonder how this compares with this type of stackup? S G S S P G S S G S %> %>I would keep high speed route off of the top and bottom layers as %>much as possible and would resize the analog and digital planes %>to avoid high speed signal traces jumping the gap. I would also %>use vias around the perimeter of the board to stitch the ground planes %>together every 0.1" or so. I never thought of lining the perimeter of the board with caps. Is that how you do it? %> %>Furthermore, you can retain the original board cost and improve things %>further if you can squeeze the signal lines into 4 layers as follows: %> %> S %> G %> P %> S %> S %> P %> G %> S I wonder how that compares with this kind of stack up? S G S P G S G S I guess the answer depends partially on how well the power plane acts as a return. %> %>Now having said all of that, the above concerns may not be your %>problem at all and changing all of this may not help. But hey, %>consider the advice worth what you paid for it! %> %>Regards, %>tony_fredriks...@netpower.com %> %> -- Thanks Again, Max
Re: Need EMC Help With Video Card
Mike, Thanks for the information. I wish I had tried moving the wires against the chassis or putting ferrites on the fan wires. I'm not sure what I could do about this from a practical view point, though, except to look for another PC. I doubt if the FCC would allow you to modify the PC. Max %> %>> I still have the problem when I remove all of the %>cables from the system, %>> including the printer cable, etc. The emissions are %>coming out of the %>> holes in the PC cabinet and this is a very good PC %>and is well sealed. The %>> largest emissions seem to be coming from the fan %>vent holes. %>> %> %> %>> mkel...@es.com %>>-- End of excerpt from Max %> %> %>Max, %>We have had problems with fans and fan vent holes very %>often. %> %>All the rules about hole sizes and emissions don't %>apply when the body of the fan is mounted right up %>against them and the fan itself is "hot" with RF. We %>have had to keep the power wiring to the fan held flat %>against the chassis and then put ferrites on it to %>choke off any pickup from emissions inside the box. %> %>Once we had to put ferrites on the fan leads from a %>Pentium cooling fan. It seemed to pick RF up %>capacitively right off the case of the Pentium it was %>cooling and then the leads radiated thruout the case. %> %>Good luck! %> %> %>-- %>Mike Donnelly %>donne...@agcs.comWD7M %>Standard disclaimer: These are my own words, not the Company's.
Re: PCI Video Card
%>From: littlew...@aol.com %> %>I would really like to review the problems that caused you to separate %>grounds. This is NOT normal practice and I am intrigued. Properly %>implemented, connection between logic and chassis dramatically reduces EME %>and improves immunity. %> %>My recommendation: Connect the grounds - CAREFULLY! I concur. My real-world experiences plus the theory involved plus what I have picked up from seminars all indicate that the return must be connected to the chassis. The only possible caveat is if you have a cabinet with a lot of holes in it. In that case, you will probably need to filter the RETURN before you connect it to the chassis. I have seen this done by running the signal and return together through a ferrite over a separated ground plane, but don't know enough about the technique to recommend it. Max mkel...@es.com
Re: Need EMC Help With Video Card
%> %> %>Max, %> %>At what frequency or band of frequencies is the problem occuring? Our video clock operates at 126 Mhz. The frequency synthesizer seems to be deriving this from a 31.5 Mhz clock, so it produces harmonics at 31.5, 63.0, 95.5, 126.0, 157.5, 189.0 220.5, 252,0, 283.5, 315.0, 346.5, etc. The only frequency that I am having problems with right now is 189.0. However, this is an interim version of the card. So, presumably, different harmonics could pop up on the next version. %> %>When you take the video cable off at the system end, the emission %>does not change? %> %>If you remove the video cable and the emission does not change, %>are there still other cables attached to the system? %> %>If there are other cables attached to the system, have you tried %>removing them one at a time or in groups to see if there is any %>one or two that are radiating the emissions? I still have the problem when I remove all of the cables from the system, including the printer cable, etc. The emissions are coming out of the holes in the PC cabinet and this is a very good PC and is well sealed. The largest emissions seem to be coming from the fan vent holes. %> %>Is there video modulation in the signal or does it look like a pure %>clock emission (narrow band, CW)? Narrow band. %> %>How well is the I/O panel of the connector bonded to the system %>back panel and how well is the D-shell of the connector tied into %>the return plane on the board. I checked this yesterday as the result of someone elses suggestion. Everything is properly bonded and well bonded. This particular PC also has EMI gasketing where the card panels mate with the cabinet panel. %> %>What method is used to isolate analog and digital power and what %>type of decoupling are you using on the analog power plane? A series ferrite with one 33uF and two .01uF and two .1uF caps on the chip side and about fourteen .01 and .1 uF caps on the otherside of the ferrite. Come to think of it, I wonder If I should have at least one larger cap in there--like maybe a 330uf tantalum for instance? %> %>Are there traces that cross the gap between analog and digital power %>and what is the nearest return path in the board stackup for each of %>these traces , if any? Are the return paths on a layer immediately %>adjacent to these signal traces and directly underneath (i.e. a ground %>plane?). The stackup is: S S P S S G S S And the power plane is broken up into two different voltage islands. So the signal layers on the power plane side of the board have a long ways to go to find a return path. I suspect that this is my problem. One idea might be to put ground traces on the signal layers where the two islands meet? %> %>While from your answer, it sounds like you've done a number of things %>to determine that it is the card/box combo without cables attached, I %>am doublechecking. %> %>Not that this can be fixed through this e-mail forum, but more info is %>better. %>It's good to see that you are smart enough to consider a qualified %>consultant as another resource to bounce the design off of. I presently have a dozen different ideas in the fire and little time to devote to this, so I don't mind paying a good consultant. I have picked up some good ideas from this group, though. The ones that seem most reasonable to me are to put an RC filter on the clock lines and to try to figure out a way to provide a better return for the clock and signal lines. %> %>Thanks, %>tony_fredriks...@netpower.com Max mkel...@es.com
Need EMC Help With Video Card
I'm presently having an EMI problem with dot clock emissions from a PC video card. Adding additional ground layers isn't an option since I'm already at the maximum. The return plane is connected to the chassis on this card and the video cables are very good. The emissions are coming right out of the box and not from the monitor or the I/O panel, or cables, etc. All of the signal layers are routed between a power and ground plane. The power plane is, however broken up into a couple of island to accomodate different voltages. All of the unused areas on the signal layers have been filled in with ground pads. The power to the RAMDAC is well isolated and physically separated from the digital signals. The digital and analog grounds are not isolated. The particular RAMDAC being used doesn't facilitate this. I'm only have a problem at one frequency and am presently measuring about 1/2 dB under the limit. I would like to be about 4 to 6 dB under. The PC that I'm using is very good for controlling emissions. The problem is with my card and not the PC. The next step that I am considering is to add guard traces along the signals carrying harmonics of the problem frequency. I'm also thinking of covering a couple of chips with cans. Another possibility is to put capacitor mounting pads at the load ends of the signal lines and try to clean up the signals a little bit. I don't have much faith in this idea though. If I did this it would be on series terminated lines with series resistors. I was thinking of using resistor mounting pads that would also accomodote ferrites and then swapping back and forth between the two. I was also think of isolating the power (with a ferrite and lots of caps) on the chip that is sythesizing the frequency and on the ones that are doing a lot of switching at the dot-clock frequency. I would appreciate any tips or ideas anyone might have. In addition, I would consider opening a PO and paying consulting fees to a PC video card guru. Max mkel...@es.com
Re: EMI Info
%> %>Good Morning everyone. %> %>I am searching for technical information on EMI, and this search has %>brought me to your site/s. I was hoping you may be able to direct me to %>sites that may contain information on EMI, not just services and products %>related to EMI. Any information would be most appreciated. %> %>I look forward to hearing from you. %> %>Regards, %> %>Eddie %> If you mean you are looking for design techniques for the control of EMI, it's very difficult to find information. For some good basic information on this subject, I recommend going to your local university library and looking through the IEEE International Symposiums on EMC. There are also a variety of seminars available--some probably more useful than others. I have found Dr. Tom Van Doren's seminars to be useful, for example. Max Kelson mkel...@es.com
Re: Voltage for 3 pahse systems
%> %>Moshe and everyone. %> %>A bit more information on the BSI document. %> %>'World Electricity Supplies". %> %>This is available from: %>British Standards Information Centre. %>389 Chiswick High Road, %>London W4 4AL %> %>tel +44 81 996 7111 / fax +44 81 996 7048 %> %>or: %> %>British Standards Institution Inc. %>Tycon Towers at Tycon Corner %>8000 Towers Crescent Drive %>Suite 1350 %>Vienna %>Virginia 22182 %>USA %> %>Tel 703 760 7828 / Fax 703 761 2770 %> %>Cost is about 33 UKP. %> %>Enjoy %> %> %>Chris Dupres %>EMC Specialist. VG Microtech. %>cdup...@vacgen.fisons.co.uk %>tel +44 (0) 1825 761077 %>fax +44 (0) 1825 768343 %>'Opinions expressed are personal, not necessarily Corporate' . . .And here's some more information: British Standards Institution 389 Chiswick High Road GB-London W4 4AL Director: Mr. B.K. Geraghty Tel: + 44 181 996 74 25 (direct) or + 44 181 996 9000 Fax: + 44 181 996 74 00 or + 44 181 996 74 48 X.400 c=gb; a=gold 400; p=bsi; o=bsi; s=surname; g=first name; Telegram: standards london w.1 Telex: 26 69 33 bsilon g Max Kelson mkel...@es.com
Re: Voltage for 3 pahse systems
Moshe, I have an old 1991 Edition of "Electric Current Abroad" published by the U.S. department of commerce that has a listing for each country. I'm not an expert in this area, so hopefully someone else can give you some more authoritative information. It looks like most European countries use 380 or 415 volts phase to phase, or something in between. It looks like a lot of other countries use 220V or 240V. In the U.S.A. we use 208V and phase to neutral potential is 120V (208/1.732=120V). Japan, as another example, is listed at 200V, while some places in the U.K. are listed as 480V. The problem that you run into is that 3-phase power supplies typically have an input rating of 180 to 264V and are not generally available to accept the higher voltages. This means that an external transformer would be required in some cases or it would be necessary to use single-phase supplies with a phase to neutral connection. Like you, I would be interested in further information in this area. Max Kelson mkel...@es.com %> %> Hello everyone, %> %> Sorry, I asked this several days ago and got no response, so maybe the %> email just didn't come through. %> %> Would anyone know what are the voltages/frequencies used in the %> various countries/environments around the world for high power %> industrial 3 phase equipment? %> %> thanks %> moshe valdman %>
Survey: Experiences with EMI Consultants
I am wondering if anyone has had experience with hiring EMI/EMC consultants to solve their problems and what sort of results they have obtained. I would be very interested in any details that anyone might be able to provide. For example, did you use a consultant after the system was prototyped or early on, during the design process. Was the consultant most useful at providing board-level, design suggestions or was he most helpful at providing after-the-fact type fixes that pertain to cabinet design and I/O cable filtering and grounding techniques, etc. Also, did the consultant, deal directly with design engineers or interface with just one person within your company, etc.? Does anyone have the names of any good consultants? Max Kelson mkel...@es.com
Do All PC Power Supplies Have Fuses?
I have an application in which a PC power supply will be placed inside a large cabinet. I will have virtually no control over the specifications of this power supply since it will be purchased from a third party. In addition, the vendors are likely to change from time to time without a lot of advanced warning. I do, of course, have veto power, though, if the supply doesn't have the necessary certifications. My question is whether I have to go to the trouble and expense of providing a circuit breaker or fuse for the supply. Or, can I, on the otherhand, simply assume that all of these supplies would have a fuse on the input. Max Kelson mkel...@es.com
"Balanced Three-Phase Equipment"
I have an old, draft copy of IEC 1000-3-2. In the definitions section (section 3.14), it states the following: 3.14Balanced three-phase equipment Equipment having rated line currents which differ by no more than 20%. Then in section 4, it classifies equipment in two 4 classes and under Class A, it says: Balanced three-phase equipment and all other equipment except that stated in one of the following classes: So, what this seems to be saying is that both "balanced" and unbalanced equipment falls under class A (if the equipment has an input power greater than 600W. I'm not really very familar with safety regulations, but this doesn't seem to make any sense to me. What is the significance of balanced three-phase equipment? What are the issues involved if the equipment presents an unbalanced load? Are there any requirements in Europe that require current balancing? Thanks, Max mkel...@es.com
Re: RFI Problems with Certified Computers
%> %>Max writes: %> %>> critical spacing distances that he recommended. With the cap connected %>> directly to VCC and ground, he also suggested a layout where traces go %>> some distance before they are connected to the DC power and return planes. Dan writes, %> %>Did Dr. Van Doren suggest that Vcc and Gnd traces should travel some %>distance or that some distance was tolerable but should be kept to a %>minimum? Everything I've ever heard, read, or experienced has taught me %>to avoid any additional inductance created by traces travelling further %>than necessary. Sure, you could get lucky and have the inductance of %>the trace solve a problem for you at one particular frequency, but %>in practice that extra inductance is a BAD thing. %> This really isn't a simple situation. Typically, the problem that you have with EMC experts and consultants (in my opinion) is that either they don't have all the answers, or they don't provide a detailed explanation because of the complexities involved, or perhaps they don't want to tell everything they know. In any case there is, obviously, more work to be done in studying bypass capacitors--both from an EMC point of view and a transient response point of view because of the new power saving technology incorporated into some of the new low voltage IC's and microprocessors. >From a basic point of view, though, capacitors can serve two completely different functional requirements: Decoupling and filtering. After that, decoupling functions can probably be broken down into at least 3 different areas. In this situation, we are really talking about circuit level decoupling and not filtering. However, there might be some filtering issues involved here also. If there are, though, they would further complicate things. In general the conclusion that Van Doren of the University of Missouri-Rolla and McCune have arrived at is that a series impedance be added to the tap off the power plane and a decoupling capacitor be provided to provide the transient response requirements. Beyond that they haven't provided any details. So, if we take this at face value then we would probably want to maximize the AC impedance while making sure the DC drop was tolerable. In that case you could maximize (not minimize) the length of the traces with the limiting factor being only the IR drop. So, there is no luck involved. If you look at it from this point of view, we are not trying to do anything that is dependent on resonance effects, etc. However, in the real world, you do have the problem of charging up the battery again (capacitor) before the IC needs the next current surge. Obviously this will require some transient (di/dt) current to flow acrossed the impedance. Presumably, this transient would be many times slower than the current transient drawn as a result of the IC's switching activities. In otherwords, the time that a device is high should always be longer than the rising edge of the waveform. Still, since there is going to be some transient (hopefully much slower), involved with refilling the cap, we would want to minimize the size of this loop also--even if it's not connected to the power or ground plane. This line of reasoning seems to lead one to a preference towards McCune's method of using discrete devices, instead of a trace, to provide the impedance. Then logically, we would want to put another capacitor on the otherside of the (ferrite) to provide the secondary current and further reduce the size of the loop. The trade off, then would be that one method requires the use of discrete components while the other one can be implemented by manipulating the trace length. The deciding factor would be whether the secondary current loop is an EMI problem. Max mkel...@es.com
Re: RFI Problems with Certified Computers
%> %> %> Hi Ladies/Gentlemen, %> %> I have been reading with interest the discussion articles on this %> subject. Since Mike Violette 04/15/96 presented his opinion on VCC/GND %> plane layout in multilayer board, the discussion seems to be focused %> on PCB EMC design. Max Kelson 04/16/96 wrote: %> %> [snip] %> What this ferrite/cap configuration would do is to force the %> oscillator to draw all transient current from the capacitor. Or, in %> otherwords, the rest of the caps on the board would be unable to help %> provide fast-transient current because of the ferrite. This would %> keep the current loop (power AND GROUND) small and prevent it from %> infecting the rest of the board. The path for the transient current %> surges would be from the capacitor to the IC's power pin, out the %> IC's ground pin and back to the negative side of the capacitor (a %> relatively small loop). %> [snip] %> %> %> It might be worthwhile to pay attention to research work done by %> professors at the Univ. of Missouri-Rolla. In the article "Power Bus %> Decoupling on Multilayer Printed Circuit Board", IEEE Trans. on EMC, %> vol. 37, pp. 155-166, May 995, they wrote: %> %> [snip] %> VI. Conclusion. %> Unlike boards without internal power and ground planes, multilayer %> boards have a built-in capacitance that is a more effective source of %> current than surface decoupling capacitors at high frequencies. In the %> time-domain, this means that most of the initial current supplied to a %> fast switching device is provided by the interplane capacitance. %> [snip] %> %> %> Regards, %> Barry Ma %> %> I attended an EMC seminar conducted by Dr. Tom Van Doren on June 8, 1992 and then another one on March 23, 1995 by Dr. Van Doren, entitled "Circuit Board Layout to reduce Electromagnetic Emission and Susceptibility. It was amazing how much progress Dr. Van Doren had made on the general subject of controlling EMC on the board level between the two dates. In this seminar the importance of a low Zo with the DC power bus was discussed extensively and there was a lot of information on bypass capacitors also. These two subjects are really the leading edge topics for EMC control in the 90's, I think. One idea that Dr. Van Doren suggested during the seminar was to connect the bypass caps directly to the VCC and ground pins. This suggestion was given with the caveat that the physical geometries be within some critical spacing distances that he recommended. With the cap connected directly to VCC and ground, he also suggested a layout where traces go some distance before they are connected to the DC power and return planes. So, in otherwords, Dr Van Doren, an EMC professor, and Earl McCune, an RF communications consultant [1] have essentially arrived at the same conclusion, I think. They are both suggesting that the loop be minimized with a bypass capacitors and that a series impedance be added in the tap off the power plane. The only difference is that McCune recommends the use of a resistor, a low-Q inductor or a ferrite while Van Doren suggests using the natural impedance of circuit board traces to provide the impedance. The question that remains unanswered, I think, is at what frequencies is this method effective and will the capacitors be fast enough to provide the current, etc. This is an issue that needs a lot of research and one of the big problems is the dynamics in the capacitor industry and the lack of appropriate capacitor specifications. Dr. Van Doren, for example, provides some sample ESL figures, in one of his calculations, of 30 nH. In other calculation, he uses 100 nH. However, I don't think he is aware that there is at least one leading edge manufacturer (AVX) that is providing SMT MLC's with very low ESR's and ESL's. As I recall AVX makes some of these capacitors with ESL's as low as about 0.7 nH. Ultimately, I think the answer has to be to use these low inductance caps to provide for an IC's high (relatively speaking) transient current requirements and use built-in caps to provide the higher frequency, lower current requirements (as mentioned previously). I highly recommend Dr. Van Doren's seminars, BTW. The information that he provides is new, and interesting and exciting. Dr. Van Doren, incidently, provides his email address in his seminar book and, as I recall, I did send him one question once and got a polite and prompt response. Max mkel...@es.com Max Kelson Peripherals Engineer Evans & Sutherland Computer Corp. [1] "Ground-Current Control Enhances Dynamic Range in High-Speed Circuits, Earl McCune, MSEE, RF Communications Consulting, EDN, January 19, 1995.
Re: RFI problems with PC's ...
[snip] %> %>It is common to see high frequency circuits on PCBs separated with %>ferrite beads and having isolated, DC-coupled 0V planes. Often, the %>oscillator is designed with its own Vcc/0V island. % [snip] This is a little bit off topic from making islands, but based on my memory of some material I've read and my own opinion, I think the following might (i.e., I'm guessing) be a good idea. With all oscillators, you could run the power (not the ground) through a ferrite. Then you would place a bypass cap to ground, between the ferrite and VCC. The ground plane would not be filtered or separated in any way--it remains in one solid piece. The net effect should be a cleaner power and ground system. What this ferrite/cap configuration would do is to force the oscillator to draw all transient current from the capacitor. Or, in otherwords, the rest of the caps on the board would be unable to help provide fast-transient current because of the ferrite. This would keep the current loop (power AND GROUND) small and prevent it from infecting the rest of the board. The path for the transient current surges would be from the capacitor to the IC's power pin, out the IC's ground pin and back to the negative side of the capacitor (a relatively small loop). Come to think of it, this EMC method would probably work with any type of IC, with the only limitation being the storage capacity and ESR and ESL of the capacitor and the impedance of the leads and via's, etc. If memory serves and I interpreted the article correctly, I think this method of keeping VCC and ground clean was described in the EDN article that I mentioned previously. Max mkel...@es.com
Re: RFI problems with PC's ...
%>Hi Max, %> %>Multi-point grounding of PCB to metal chassis is a good idea. %> %>The beneficial effect of the multi-point connection of the PCB to a %>metal chassis is to reduce the net impedance associated with the %>return currents for signals flowing on the PCB. The impedance decrease %>provides a lower voltage generated across the printed circuit board, %>thus reducing the common mode present on the various circuit nodes on %>the board. %> %>This is especially critical as frequencies rise, regardless of the %>concern often raised about (the red herring of) "ground loops". [snip] Mike, Thanks for the great info. I have had similar experiences and problems in trying to avoid the red-herring of ground loops. We had one product, for example, in which I used BNC's with built-in 10,000 pF decoupling capacitors. I'm sure these connectors were well designed, but we had to remove them and replace them with regular "grounded" BNC's in order to pass EMI tests. In those days we didn't have to do the susceptibility testing, so I don't know how well these decoupled caps work for the new 61000 tests. I expect they could be a problem since discharges placed on the shield could go directly to the circuit ground plane (or traces). YEE GADS! I WONDER IF THAT COULD REALLY HAPPEN? In the case of high-frequency ground loops, like with video, BTW, I don't think there are any ground loops. High frequency returns always follow the signal path (if they can) because this is the path with the least impedance. Therefore, I don't think the familar argument that currents will return through the power cord to the driver are pertinent. Low frequency signals (kHz range) can return via the power cords, but I doubt if this is a problem with computer systems. If there is a potential problem here, though, I would be very interested in knowing about it. Max Max Kelson mkel...@es.com
Re: RFI problems with PC's ...
[snip] %> %> 4. I hope the "big name" PC makers EMC engineers are also listening in %> on us (some have also commented). I know they are doing their best in %> better electronic design (e.g. multipoint grounding of the main board %> - something I saw on some new PC's) and I don't think I can personally %> help much in this area. I think we should help them convince their %> bosses it is required to put a higher priority on the long term EMC %> performance (i.e. mechanical packaging design). %> %> thank you all again for your cooperation %> %> moshe valdman %> mgr - EMC, Safety, Reliability and Components Engineering %> Scitex Israel [snip] I have also noticed that some PC's have massive, multipoint connection of the return plane(s) to the chassis. In fact, it's something that I am thinking of doing in our next product. Has anyone had any experience with this EMC technique? Does anyone know if there are any caveats to watch for or any potential performance problems? BTW, as the culprit, who first brought up the term "big name", I am starting to have some regrets. Actually, all the two-letter/three-letter PC's that I have tested have done quite well--I wasn't thinking of those. I was thinking, instead, of some of the super, high-volume manufacturers and system integrators, etc. I apologize for that confusion, sorry. Max Max Kelson mkel...@es.com
Re:
Jon, That's great information--I also anticipate a requirement for heavy industrial immunity in the future and have been wondering what problems I might be in for. With PCs (and computers in general), isn't it the case that if the cables are shielded and grounded to the cabinet there isn't likely to be a problem? For emissions, BTW, I have also had good luck with DEC. Max Kelson mkel...@es.com %> %>I have tested systems to the heavy industrial immunity specification which %>included class B PCs. Both HP Vectra computers and Dell computers faired %>well. Ocassionally the monitors sold with these systems are disturbed to %>the point of turning themselves off (a failure in most books). To date %>I've always been able to solve this problem by upgrading to an NEC %>multisync monitor. The key distinquinction of all these products is that %>they really do meet class B by wide margins and use very good shielding to %>get to that level. Once you have shielding that good and use digital %>techniques inside (as opposed to small signal, high impedance analog %>signals - thermocouples, etc.) heavy industrial immunity compliance is %>usually a given. %> %>Jon D. Curtis, PE %> %>Curtis-Straus LLC j...@world.std.com %>One-Stop Laboratory for EMC, Product Safety and Telecom %>527 Great Roadvoice (508) 486-8880 %>Littleton, MA 01460 fax (508) 486-8828 %>http://world.std.com/~csweb %>On Wed, 12 Feb 1997, Tony Fredriksson wrote: %> %>>
Measuring AC
Does anyone know of a good method (or have any ideas) of how I could reduce line voltage down to low (DC) levels in order to measure the line voltage with an AD converter. Using a transformer is obviously the easiest way and probably provides the least potential problems with safety agencies. But transformers are not (I don't think) terribly accurate and they are rather bulky even in this sort of application. What are the safety implications, for example, of just rectifying and filtering the voltage and running it through a voltage divider? Thanks, Max Kelson mkel...@es.com
re: Measuring AC
I want to thank everyone for the great information I got in response to my question about measuring AC. One thing I hadn't thought about with my off-the-cuff idea of simply using a voltage divider is the issue of isolating the AC return and the circuit board return. Not isolating these raises a variety of issues that I'm not prepared to deal with. So, I think they need to be isolated. The method suggested by Jonathan Malton strikes me as a really elegant and highly accurate solution to the problem. This involves the use of a voltage controlled oscillator and an optoisolator. Using op-amps for rectifying diodes is also a great idea I think. The problem of providing a separate off-line power supply for the VCO, sort of takes some of the fun out of the idea, but this problem is, nevertheless manageable. I'm also going to review IEC950 and IEC1010 as suggested by Horst Haug. The basic problem with transformers is that it's not possible to get a specification on their accuracy. In talking to Signal Transformer, they give me a verbal specification of +/-2% accuracy (no load). Advanced Components Industries, OTH, provide a verbal specification of +/-10%. The difference might be in the size of the transformers. The Signal transformer is relatively large and relatively expensive. The Advanced Transformer is of the PCB type and is very small (0.6 inches high). The lady at Advanced seems to be very knowledgeable and says that the accuracy is not simply a function of turns ratio, but also depends on the wire and core construction. She claims that they can calculate transformer accuracy simply by looking at the wire and core specifications. Max mkel...@es.com
Re: Re[2]: Measuring AC
%> %> %> I suspect (but don't know for sure) that the accuracy of a transformer is %> the way it performs, relative to it's spec's, rather than relative to its %> history. That is, a _given_ transformer may be extremely accurate once %> calibrated, but the _initial_ accuracy may be difficult to predict. Yes, that's my understanding also. A manufacturer, for instance, could, perhaps buy two separate batches of cores (for use with one batch of wire) and all of the voltages from the transformers made with the first batch would be extremely close together and all of the voltages from the transformer made with the second batch would be extremely close together, but the delta between the two different transformer batches could vary by as much as 20%. With 10V transformers, for instance, batch number 1 might result in voltages of 9V +/- .1% (just guessing) and batch number 2 might result in voltages of 11V +/- .1% %> Adding %> some calibration mechanism on each board can be expensive, but if you want %> a highly accurate reading of line voltage, you may have to do this anyway. Yes, I expect that a calibration procedure would result in extremely accurate measurements, but would require measurement of the output of each transformer. %> %> Jonathan Malton %> S-S Technologies, Inc. %> Kitchener, Ontario, Canada %> %> "I'm not so arrogant as to suggest that my opinions are corporate policy" %> %> %> Max Kelson mkel...@es.com
Re: Salary of Safety Professionals
%> %>I really don't know if this forum is the place to discuss the subject, %>but I'm curious about competitive salaries for safety and compliance %>professionals (my review is coming up and I need a negotiating %>position). If anyone knows of any surveys specific to the field, %>please let me know. If not, then if you have any suggestions on how to %>collect data by email anonymously, let me know and I'll be glad to do %>it. The specific information I think is needed for a survey includes: %> %>1. job title %>2. years of experience (overall and safety related) %>3. level of education (non degreed, BA, BS, MS, Ph.D.) %>4. professional credentials (PE, CSP, etc.) %>5. Type of employer (Government, Agency, Consultant, Manufacturer) %>6. size of employer (small =<200, med = 200-1000, large =>1000) %>7. location (US West, SW, South, East, Midwest, Asia, Europe, other) %>8. Gross salary assuming usual benefits (health care, vacation, etc.) %> including bonuses. All in US dollars. %> %>If anyone sends me this data about themselves, I'll compile it in an %>unscientific sort of way and report back the results without any names. I saw a magazine page posted on a cubicle wall a few months ago with the average salary of a variety of professions in the electronic field. I think the figure for compliance engineers was $56K (not sure). Max Kelson mkel...@es.com
Re: Input power connections w
Here's another experience that is non-industrial, but educational. About 8 years ago I build a large addition on my home. Since then, one thing has led to another and I have never "got around to" installing a furnace. The room is well insulated and relatively warm anyway, so I use two freestanding electric heaters when it gets exceptionally cold. These are the 1200W/1500W type I think . These are the 1200W/1500W type I think. The first big mistake I made was putting them on the same circuit. (I could have sworn that when I wired the room, I put those two outlets on separate circuits). Not long after that one of the heaters began operating intermittantly. When you wiggled the wall plug the heater fan speed changed, etc. Disassembly of the outlet indicated massive damage to the outlet at the spring connection terminals. The wire was also damaged for a couple of inches. Luckily I had left about six inches of total wire in the box, so I was able to cut off the damaged wire and install a new outlet. In addition, I had to remove all of the other outlets on the circuit and replace them with screw type terminals. I think those outlets were safety approved, but the moral to that story, I think, is don't use outlets with spring connectors. I don't think they can safely carry 20-A. About 6 months after that I was sitting in my room watching TV, with a heater on, and sparks began jumping out of the heater. I reached down and quickly turned it off. Turning the switch off didn't help--it just kept right on throwing sparks until I pulled the plug. Since then I have always unplugged the heaters when they aren't in use. One of the heaters is on a "heavy-duty extension cord". After some period of use, the connectors on both ends of the cord started getting very warm to the touch. I replaced these connectors and the connector on the end of the heater cord and it solved the problem. Ignoring my own initial mistake of using a single-circuit, I would say that my other problems have been a result of poor testing by the safety agency of the spring-type terminal outlets and the low-quality connectors that come on the ends of power cords. Max
Re: Immunity/Cables
Steve, %>Max, the amount of immunity a cable has is dependent upon the type of %>shielding it has and how well it is connected to the case ground. I have gone %>through a whole bunch of gyrations with the cable vendors I work with (my %>other responsibility at this company is high-speed signal cable development) %>in order to build EMC-tight cables. %> %>If the cable is built and grounded well, then the likelyhood of a failure due %>to the effects of outside radiation is very low. %> %>Steve Chin %>StreamLogic Corp. %>Menlo Park, CA, USA %> That's been my experience also with PC's, workstations. I haven't ever tested anything to a severe industrial level, though. However, I assume there wouldn't be a problem if the cables were well shielded and connected to the chassis. This raises another interesting question concerning the connection of the return to the chassis. Years ago I did a survey of a variety of monitor manufacturers to see if any of them used differential input. All of them said no. In addition, I have checked PC's and workstations from many manufacturers and never found any that didn't have the (video) cable return connected to the case. I assume, however, that without this connection of return to the cabinet, a system would probably flunk emission tests as well as immunity tests. Has anyone had any experiences in this area? Thanks, Max Max Kelson mkel...@es.com
Re: Spread spectrum clock oscillator
There was an article on these in the 1994 IEEE Sym on EMC. It was written by 3 authors from "Lexmark International, Inc.", Lexington, KY. So, if you can track them down you might get a lead. In the article they have a picture of an IMI chip, BTW. I have looked at emissions from a variety of personal computers with a spectrum analyzer over the last few years and they all seem to have the characteristic, wide-band, flat-top waveform that "SSCGs" produce. So, I would guess that IMI isn't the only one that makes these. I, for one, would also be very interested in having the names of some vendors and information on SSCG effectiveness. Max Kelson mkel...@es.com %> %>Does anyone know of a source for a spread spectrum clock oscillator. %> We have a sample of a 20MHz spread spectrum oscillator that we find %> reduces radiated emissions readings from our products by several dB. %> The company name was IMI in Milpitas, California, but no longer %> exists. Any leads to a similar product would be greatly appreciated. %> %>Thanks, %>Darrell Upson %>Xerox ColorgrafX Systems, Inc.
Re: Spread spectrum clock oscillator
Keith, Thanks for the great information. I see that you are one of the authors of the excellent IEEE article. Have you written any other articles that you might want to call our attention to? Max mkel...@es.com Max Kelson Peripherals Engineer Evans & Sutherland Computer Corp. %> %>Max, %> %>1) IMI is still in Milpitas, CA and their phone number is (408) 263-6300 with %>web page http://www.IMICorp.com/. ICWorks also makes some spread spectrum %>parts and their number is (408) 922-0202. %> %>2) Most PCs these day's are using synthesizers for clock generation and all %>jitter to some extent. However if the part is not intended to create a spread %>spectrum output they may not reduce the emissions at all. Take a simple case %>where a clock frequency is stable for 1ms and then deviates for 1s over a range %>of frequencies. A spectrum analyzer would show a flat top in max hold mode but %>the EMI receiver will give a reading at the 1ms stationary frequency the exact %>same value as a clock that is not modulated. The true spread spectrum output %>can reduce emission from 0-20dB or more depending on deviation and measuring %>frequency. %> %>3) There have been several publications on the subject. %> a) Digital Circuit Radiated Emission Suppression with Spread Spectrum %>Techniques, .ITEM 1994. %> b) Spread Spectrum Clock Generation for the Reduction of Radiated Emissions, %>1994 IEEE EMC Symposium. %> c) A Study o the Interference Potential of Spread Spectrum Clock Generation %>Techniques, 1995 IEEE Symposium. %> d) EMC New watch pages 15-17, Compliance Engineering, May/June 1995. %> e) EMC New watch pages 74-75, Compliance Engineering, July/August 1995. %> f) Electromagnetic Interference Control Using Solid-State Technology, %>pages37-39, Compliance Engineering, May/June 1995. %> %> %>I am sure there are more. %> %>Keith Hardin %>Lexmark International Inc. %> %> %>>There was an article on these in the 1994 IEEE Sym on EMC. It was %>>written by 3 authors from "Lexmark International, Inc.", Lexington, KY. %>>So, if you can track them down you might get a lead. In the %>>article they have a picture of an IMI chip, BTW. %> %>>I have looked at emissions from a variety of personal computers with a %>>spectrum analyzer over the last few years and they all seem to have the %>>characteristic, wide-band, flat-top waveform that "SSCGs" produce. So, %>>I would guess that IMI isn't the only one that makes these. %> %>>I, for one, would also be very interested in having the names of some %>>vendors and information on SSCG effectiveness. %> %>>Max Kelson %>>mkel...@es.com %>%> %>%>Does anyone know of a source for a spread spectrum clock oscillator. %>%> We have a sample of a 20MHz spread spectrum oscillator that we find %>%> reduces radiated emissions readings from our products by several dB. %>%> The company name was IMI in Milpitas, California, but no longer %>%> exists. Any leads to a similar product would be greatly appreciated. %>%> %>%>Thanks, %>%>Darrell Upson %>%>Xerox ColorgrafX Systems, Inc. %> %>
How Do You Calculate/Estimate Audible Noise?
Does anyone happen to know how to calculate or estimate the audible noise level of products (A-weighted) before they are built? One assumption that I have made is that continuous acoustical noise from numerous identical devices add together in the same way that power does. IOW, two identical fans, with a 50 dBA rating, would measure 53 dB. Is this correct? Does this represent a worst-case estimate? Or, IOW, in an actual system with 10 fans, for example, would some of the noise cancel out due to phase angle differences in the emissions from the fans? Another question that I have is if emissions at different frequencies add together like power. For example, would 50 dBA "noise" emissions, at 15 Khz, from a violin add together with 50 dBA emissions, at 20 Hz, from an organ to make a total measured emission of 53 dBA? Or would a meter measure only 50 dBA in this situation? Or more specifically, has anyone had any experience with power supply fans and system cooling fans? Does the noise from these two different types of fans typically add together? Max Kelson Evans & Sutherland
RE: golden computers
I did some tests using an HP Vectra 2 or 3 years ago and found that it was indeed very good. However, I later found a Digital Celebris XL590 that was even better. This computer would be obsolete by now so I would be interested in hearing from anyone who has used a newer Digital model. Someone mentioned that they have had problems with monitors in the past. I have also. It requires some work, but what I have done in the past is to get a copy of all the video formats that will be used. I then look at the number of horizontal pixels that are used to create a character and calculate the expected emission frequencies from that data in advance. The frequency coming from the monitor can obviously be slowed down by switching to larger characters and this will reduce emissions. My problem, though, is that I have never really been sure what is legal (or ethical) when it comes to increasing the size of the characters. As I recall, I think I settled for about 80-100 characters across the entire width of the screen. In reality a typical PC user would probably use smaller characters. In any case, I tend not to worry about it (rightly or wrongly) since the monitor already has a class B sticker and is not the device under test. Max Kelson -Original Message- From: jim.nado...@amp.com [SMTP:jim.nado...@amp.com] Sent: Friday, June 27, 1997 6:35 AM To: emc-p...@ieee.org Subject:golden computers I wanted to thank all the folks who responded to my request for info on quiet PC's for peripheral testing. The info is quite valuable and helps to provide some direction. The result was that the clear favorite was the HP Vectra... Jim Nadolny
RE: Re[2]: Upcoming EMC Seminar
I would vote to allow a continuation of posting of EMC/safety seminars. This is valuable information and Henry Ott, for instance, is certainly a prestigious contributor to the field. On the flip side, though, I believe that EMC and safety consultants have some obligation to make contributions to this forum and it seems like they never do. In addition, the papers they submit to the journals seem to sometimes lack the detailed information that would make them useful in a practical sense. Even in their seminars some of these experts seem to prefer to simply grind out the same old basic and abstract stuff while saving the more useful information for some "special" or "separate" seminar costing still more money. The bottom line, I guess, is that we should start asking them to participate in this forum, when appropriate, in exchange for advertising privileges. I suggest members should also provide negative feedback on seminars that don't provide practical, useful information, substantiated by emissions tests. Max Kelson mkel...@es.com -Original Message- From: Jim Hulbert [SMTP:hulbe...@pb.com] Sent: Wednesday, February 11, 1998 8:56 AM To: emc-p...@ieee.org; richard_c...@iris.scitex.com Subject:Re[2]: Upcoming EMC Seminar According to the Charter and Guidelines (10 March 1995) "blatant or overt advertising of goods or services is not permitted". I think this is a good rule. This should not be a forum for "free" advertising. There are plenty of other appropriate avenues for people to advertise their goods and services. Jim Hulbert __ Reply Separator _ Subject: Re: Upcoming EMC Seminar Author: "Richard Cass" at SMTPGWY Date:2/10/98 8:21 AM I thought that blatant advertising of services, including FOR PROFIT seminars, was not allowed on EMC-PSTC forum. Am I wrong? Regards, Richard Cass __ Reply Separator _ Subject: Upcoming EMC Seminar Author: mlwald...@aol.com at INTERNET Date:2/10/98 4:29 AM We just wanted to take this opportunity to let every one know that there are still a few seats available to attend the EMC Seminar being presented by Mr. Henry Ott and hosted by RhienTexas, Inc. For further information check out the web page at www.rheintech.com/seminar.html. Those of you that wish to attend are urged to register by Febrauary 20, 1998. There is a correction that must be noted about the information provided on the above web page, the price for this two day seminar is not $750 it is $675 per participant. Thank you, Murrell Waldron RhienTexas, Inc. 1701 E Plano Pkwy, Suite 150 Plano, TX 75074 P: 972-509-2566 F: 972-509-0073 email: mlwald...@aol.com
