Re: Component Qualification
Tony, we have an EMScan, and found it to be of limited use. If you have a board with components that protect peripheral interfaces, you really need to test with the interfaces present in the same fashion that you would run a Qual test. A precompliance facility does a better job than EMScan for this. If your looking for where a particular frequency is present on a board, the EMScan does a nice job of this. The picture is easier to interpret than probing with close field devices. Any questions, contact me directly Best regards, Derek Walton --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Component Qualification - Thanks
Hi, Thanks to all that has responded to my questions and providing your precious advice. Regards Koh --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Component Qualification: Ferrite Formula
Koh, I'm afraid your formula won't work. The attenuation provided by the ferrite bead is directly dependant on the system source and load impedance at the particular frequencies, which won't generally be known. Without knowing the system impedances, you can't calculate directly what the insertion loss change will be when the bead impedance is changed, even though the system impedance doesn't change. However, you can do some worse case studies by assuming a range of source and load impedances. For example, the measurement standard of 50 ohms provides a reduction of 0.93dB for the worse case change of 67ohms to 50 ohms at 68MHz. Beads provide less attenuation at higher source and load impedances, so if you had a 1000 ohms system, the change would reduce to just 0.14dB. However, if the system impedance were as low as 10 ohms, which is probably unlikely, the reduction would increase to 2.16dB. Even this approach assumes resistive source and loads, and a resistive bead, but is at least a guide. Regards, Jeff - Dr Jeff Chambers Westbay Technology Ltd Suppliers of EMC Design Software Tel: +44 1229 869 108 Fax: +44 1229 869 108 http://www.westbay.ndirect.co.uk/westbay1.htm j.chamb...@ndirect.co.uk Main St Baycliff Ulverston Cumbria LA12 9RN England - -Original Message- From: Koh Nai Ghee koh...@cyberway.com.sg To: Maxwell, Chris chr...@gnlp.com; 'Ralph Cameron' ral...@igs.net; Tony J. O'Hara tonyoh...@compuserve.com; Paolo Roncone paolo.ronc...@compuprint.it Cc: EMC-PSTC emc-p...@majordomo.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: 21 September 2000 18:14 Subject: Re: Component Qualification Chris other, Thanks for the reply. Chris has given a great alternate method. I would like further add on to this test method/approach. Those second source components (ferrite or oscillator) that we get of course have to meet the PCB footprint as well as meeting the primary specification. For ferrite, let's now say the second source component has the correct impedance at 100MHz and current rating. However, the impedance curve of ferrite from different source are mostly of different response curve. It would be difficult to judge whether does it degrades the final product emission level. In view of this, I might add that we can make use of the final product scanning results for a guide to make a final judgement. For example, if the final product has operating frequencies of 34MHz, the worst three case frequencies are 68MHz, 102MHz 136MHz with passing margin of 4dB, 2dB 6dB margin. Comparison of the ferrite bead impedance at these frequencies yield the following reading, Freq1st source2nd source 68 67 ohm 50 ohm 10298 ohm 96 ohm 13680 ohm 85 ohm How can we have a simple calculation to state that this 2nd ferrite is OK on the product? I would like to hear your view of such formula dB change = 20 log (1st impedance) - 20 log (2nd impedance) At 68MHz, dB change = 20 log 67 - 20 log 50 = 2.54 dB With this 2.54dB, the final product is still passing with 4-2.54 = 1.45dB. Same for 102MHz yield 1.82dB and 136MHz yield 6.53dB passing. Would this be the worst case scenario that will occur? How's the group view on such approach? Regards Koh --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Component Qualification: Ferrite Formula
Koh, I'm afraid your formula won't work. The attenuation provided by the ferrite bead is directly dependant on the system source and load impedance at the particular frequencies, which won't generally be known. Without knowing the system impedances, you can't calculate directly what the insertion loss change will be when the bead impedance is changed, even though the system impedance doesn't change. However, you can do some worse case studies by assuming a range of source and load impedances. For example, the measurement standard of 50 ohms provides a reduction of 0.93dB for the worse case change of 67ohms to 50 ohms at 68MHz. Beads provide less attenuation at higher source and load impedances, so if you had a 1000 ohms system, the change would reduce to just 0.14dB. However, if the system impedance were as low as 10 ohms, which is probably unlikely, the reduction would increase to 2.16dB. Even this approach assumes resistive source and loads, and a resistive bead, but is at least a guide. Regards, Jeff - Dr Jeff Chambers Westbay Technology Ltd Suppliers of EMC Design Software Tel: +44 1229 869 108 Fax: +44 1229 869 108 http://www.westbay.ndirect.co.uk/westbay1.htm j.chamb...@ndirect.co.uk Main St Baycliff Ulverston Cumbria LA12 9RN England - -Original Message- From: Koh Nai Ghee koh...@cyberway.com.sg To: Maxwell, Chris chr...@gnlp.com; 'Ralph Cameron' ral...@igs.net; Tony J. O'Hara tonyoh...@compuserve.com; Paolo Roncone paolo.ronc...@compuprint.it Cc: EMC-PSTC emc-p...@majordomo.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: 21 September 2000 18:14 Subject: Re: Component Qualification Chris other, Thanks for the reply. Chris has given a great alternate method. I would like further add on to this test method/approach. Those second source components (ferrite or oscillator) that we get of course have to meet the PCB footprint as well as meeting the primary specification. For ferrite, let's now say the second source component has the correct impedance at 100MHz and current rating. However, the impedance curve of ferrite from different source are mostly of different response curve. It would be difficult to judge whether does it degrades the final product emission level. In view of this, I might add that we can make use of the final product scanning results for a guide to make a final judgement. For example, if the final product has operating frequencies of 34MHz, the worst three case frequencies are 68MHz, 102MHz 136MHz with passing margin of 4dB, 2dB 6dB margin. Comparison of the ferrite bead impedance at these frequencies yield the following reading, Freq1st source2nd source 68 67 ohm 50 ohm 10298 ohm 96 ohm 13680 ohm 85 ohm How can we have a simple calculation to state that this 2nd ferrite is OK on the product? I would like to hear your view of such formula dB change = 20 log (1st impedance) - 20 log (2nd impedance) At 68MHz, dB change = 20 log 67 - 20 log 50 = 2.54 dB With this 2.54dB, the final product is still passing with 4-2.54 = 1.45dB. Same for 102MHz yield 1.82dB and 136MHz yield 6.53dB passing. Would this be the worst case scenario that will occur? How's the group view on such approach? Regards Koh - Dr Jeff Chambers Westbay Technology Ltd Suppliers of EMC Design Software Tel: +44 1229 869 108 Fax: +44 1229 869 108 http://www.westbay.ndirect.co.uk/westbay1.htm j.chamb...@ndirect.co.uk Main St Baycliff Ulverston Cumbria LA12 9RN England - --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Component Qualification
Tony: I have sold these systems and also used them and they are good for graphing a profile of a scanned board and giving the field intensity vs postion over the board area. You can quickly find trouble spots using the computer interface. Ralph Cameron - Original Message - From: Tony J. O'Hara tonyoh...@compuserve.com To: Koh Nai Ghee koh...@cyberway.com.sg Cc: EMC-PSTC emc-p...@majordomo.ieee.org Sent: Wednesday, September 20, 2000 4:42 PM Subject: Re: Component Qualification You may want to look at using a PCB Electromagnetic Scanning System! One of the advertised uses for these test devices is for quickly comparing EMC performance when component changes are made etc.! I believe there are 4 different manufacturers who make these devices. The one that I'm just starting to learn about is made by EMSCAN in Canada. Their web is www.emscan.com Maybe someone who has uses one of these scanners can provide an experienced viewpoint? Regards Tony Colorado --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
RE: Component Qualification
Wait a minute! Buying a board scanning system to evaluate different vendors for ferrites and oscillators? My company doesn't have that kind of money to throw around. These systems can cost 10's of thousands of dollars. Ferrite beads cost about a dime for a dump truck load. If it costs $10,000 to evaluate a second source for ferrites, I 'll stick with the ferrites I have. I'd like to offer a lower cost alternative. Koh Nai asked about what specifications were important for qualifying alternate sources for ferrites and oscillators. When it comes to ferrites, I look at three things: I look at the PCB footprint (it won't work if it won't fit). I look at the impedance curve and the current capacity. If all three of these specifications are equal or better than what I need, I accept them. I don't even consider re-testing for emissions if I have checked these three specifications. Alternate sources for ferrites can be qualified for the cost of reading a spec sheet. Oscillators are a different story. When one of my digital design colleagues wants to change oscillators. They consider its PCB footprint, the output frequency, its ambient stability, its temperature stability and its load driving capability. If it meets their needs; then I take a circuitboard with the existing oscillator and run a near field probe over it near the oscillator until if find a location of maximum near field emissions. (If you really are strapped for cash, you can make your own near field probe.) I write down the exact position and orientation of the near field probe and I either print out or write down the spectrum analyzer readings. I then put the new oscillator on the exact same board and repeat the experiment. If the measurements are close (within a dB or two) I don't worry. If the measurements are more than 4 dB higher, then I look further. Then I consider: testing the whole unit with the new oscillator with my antenna set up 1 meter away in-house, or re-testing the unit for emissions at an OATS, or not using the new oscillator. ONE WARNING: if the new oscillator is at a different frequency, then the method above WILL NOT yield any useful results. One thing that we have done with new designs is to put a 1206 surface mount PCB footprint in line with the oscillator output. We start our testing with a 0 ohm resistor. If we run into problems, we can put either a ferrite bead or higher value resistor in this position to cool off the oscillator. This has worked well with oscillators under 100MHz. I don't know if it will work for faster oscillator. I know that there are problems with using near field probes to make such correlations, however using a board scanning device would cost much more than a near field probe and still only be measuring near fields. Even so, if I had the budget, I'd love to try one out. To me, the real method of doing this starts with the initial testing of your product. I try to get more than a 5dB margin during the initial testing. With these margins, I don't need to worry so much about component differences. I know that this is sometimes not possible. I have sacrificed margins in order to get a product's testing done and released (I don't get paid if we don't ship.) The problem is, without margins, I need to worry more about component differences. Another point to remember is that EN 55022 and other emissions standards go by the 80 % rule. A product passes if we are confident that 80% of the units that we ship meet the emissions requirements. Anybody who wants to dispute whether your units pass or not is REQUIRED to test up to 7 samples in order to get enough data to use statistical methods to compute the confidence factor. One failing unit does not equal a guilty verdict. (Of course, if one unit is failing by 20dB, that's a problem.) The people at CISPR put this slack into the limits to allow for slight component differences and measurement uncertainty. They allowed us the slack, but it is our responsibility to use it with common sense. These are my two cents worth and definitely don't reflect the opinions of my employer. (Why would they need me if I thought the same way they do?) Have a great day! Chris Maxwell, Design Engineer GN Nettest Optical Division 6 Rhoads Drive, Building 4 Utica, NY 13502 PH: 315-797-4449 FAX: 315-797-8024 EMAIL: chr...@gnlp.com -Original Message- From: Ralph Cameron [SMTP:ral...@igs.net] Sent: Wednesday, September 20, 2000 11:16 PM To: Tony J. O'Hara; Koh Nai Ghee Cc: EMC-PSTC Subject: Re: Component Qualification Tony: I have sold these systems and also used them and they are good for graphing a profile of a scanned board and giving the field intensity vs postion over the board area. You can quickly find trouble spots using the computer interface. Ralph Cameron - Original Message - From: Tony J. O'Hara tonyoh...@compuserve.com To: Koh Nai Ghee koh...@cyberway.com.sg Cc
Re: Component Qualification
Chris, Don't get me wrong. I didn't read the full text of the application and merely supported the utility of the EMSCAN system. If you know of sources where you cn get ferrites, specifically ferrite toroids for a dime a dump truck, I'd be interested. In the past two years my costs for them have more than tripled as the mfr now uses dealers who have minu\imum quantities which are out of sight for the small vendor. With the heavier weights , shipping costs skyrocket. I like your methods of determining ferrite application and how to look for hpt spots. My opinions are my own since I work for me. regards Ralph Cameron EMC Consultant and Suppression of Consumer Elecronics (after sale). - Original Message - From: Maxwell, Chris chr...@gnlp.com To: 'Ralph Cameron' ral...@igs.net; Tony J. O'Hara tonyoh...@compuserve.com; Koh Nai Ghee koh...@cyberway.com.sg Cc: EMC-PSTC emc-p...@majordomo.ieee.org Sent: Thursday, September 21, 2000 7:58 AM Subject: RE: Component Qualification Wait a minute! Buying a board scanning system to evaluate different vendors for ferrites and oscillators? My company doesn't have that kind of money to throw around. These systems can cost 10's of thousands of dollars. Ferrite beads cost about a dime for a dump truck load. If it costs $10,000 to evaluate a second source for ferrites, I 'll stick with the ferrites I have. I'd like to offer a lower cost alternative. Koh Nai asked about what specifications were important for qualifying alternate sources for ferrites and oscillators. When it comes to ferrites, I look at three things: I look at the PCB footprint (it won't work if it won't fit). I look at the impedance curve and the current capacity. If all three of these specifications are equal or better than what I need, I accept them. I don't even consider re-testing for emissions if I have checked these three specifications. Alternate sources for ferrites can be qualified for the cost of reading a spec sheet. Oscillators are a different story. When one of my digital design colleagues wants to change oscillators. They consider its PCB footprint, the output frequency, its ambient stability, its temperature stability and its load driving capability. If it meets their needs; then I take a circuitboard with the existing oscillator and run a near field probe over it near the oscillator until if find a location of maximum near field emissions. (If you really are strapped for cash, you can make your own near field probe.) I write down the exact position and orientation of the near field probe and I either print out or write down the spectrum analyzer readings. I then put the new oscillator on the exact same board and repeat the experiment. If the measurements are close (within a dB or two) I don't worry. If the measurements are more than 4 dB higher, then I look further. Then I consider: testing the whole unit with the new oscillator with my antenna set up 1 meter away in-house, or re-testing the unit for emissions at an OATS, or not using the new oscillator. ONE WARNING: if the new oscillator is at a different frequency, then the method above WILL NOT yield any useful results. One thing that we have done with new designs is to put a 1206 surface mount PCB footprint in line with the oscillator output. We start our testing with a 0 ohm resistor. If we run into problems, we can put either a ferrite bead or higher value resistor in this position to cool off the oscillator. This has worked well with oscillators under 100MHz. I don't know if it will work for faster oscillator. I know that there are problems with using near field probes to make such correlations, however using a board scanning device would cost much more than a near field probe and still only be measuring near fields. Even so, if I had the budget, I'd love to try one out. To me, the real method of doing this starts with the initial testing of your product. I try to get more than a 5dB margin during the initial testing. With these margins, I don't need to worry so much about component differences. I know that this is sometimes not possible. I have sacrificed margins in order to get a product's testing done and released (I don't get paid if we don't ship.) The problem is, without margins, I need to worry more about component differences. Another point to remember is that EN 55022 and other emissions standards go by the 80 % rule. A product passes if we are confident that 80% of the units that we ship meet the emissions requirements. Anybody who wants to dispute whether your units pass or not is REQUIRED to test up to 7 samples in order to get enough data to use statistical methods to compute the confidence factor. One failing unit does not equal a guilty verdict. (Of course, if one unit is failing by 20dB, that's a problem.) The people at CISPR put this slack into the limits to allow for slight component differences
R: Component Qualification
Dear Koh: My opinion is that first you should distinguish between active components (like oscillators, but also EMC sensitive parts like microprocessors, memories, ASIC's and all fast logic IC's) and passive components (like ferrites). For the first type, in any case you cannot be enough confident about the goodness of second source components without testing. My experience tells me that even same vendor, same-all active components can have significant spreads in EMC behavior, because of the parasitic (and often uncontrolled) parameters involved. That is especially true for radiated emissions. I remember having sometimes nasty surprises when testing products with identical components that were just from different mfg batches. One typical example is the edge rate (rise/fall times) that is usually specified relative to maximum values but not at all for minimum values. So even if the edge rates in the data sheets are identical, you can get different EMI behaviors (even from the same vendor). As for passive components (like ferrite beads, resistors, capacitors etc. used to filter noise at the PCB level) I think you can go with just looking at the data sheet, but I would recommend that you test if there is even a small difference in impedance curves (that could trigger unexpected resonances or change the emissions profile). Whenever the purchase dept guys approach me with second (or third) source EMI-sensitive components (like those that you mention) I follow these steps: 1. First screening based on data sheet (example impedance curves for ferrites). If they at least don't match those of the already qualified/tested components they are discarded. If they look the same or even better (example: higher impedance for ferrites or higher resonance frequency for capacitors) I go on to step 2. 2. Test Just my opinion... Hope this helps. Paolo -Messaggio originale- Da: Koh Nai Ghee [SMTP:koh...@cyberway.com.sg] Inviato:martedì 19 settembre 2000 22.48 A: EMC-PSTC Oggetto:Component Qualification Group, Can anyone advice on any guide for checking/qualifying second source component, such as crystal, oscillator ferrite bead, mounted on product is still meeting the emission limits? We are manufacturer of pheripherals cards. Some card has crystal and/or oscillator for digital circuitry. Ferrite bead are used too. As these component will affect the final product EMI level, therefore some qualification/guide in terms of EMI must be considered when qualifying second source component. These components are used in lots of product that we made, it would be costly to perform scan for every model. Every product are tested and pass EMI with initial source components. Can we just made a comparison of the specification of the first source compnent with this second source? If yes, what are the crucial specs/information that must meet the first source component? For crystal/oscillator, beside the Frequency stability tolerance specs, what other item is crucial. For Ferrite bead, impedance curve, what other item is crucial. If happens that some specs are slightly out, e.g. 2nd source crystal are having 5PPM more than initla source crystal, Can we make use of the product passing margin, say 3dB, and do some calculation to confidently say that the second source component on the card is still EMI compliance. Likewise for oscillator and ferrite bead. If yes, could you advice on an example of such calculation. Many thanks in advance for the replies. Regards Koh --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Component Qualification
You may want to look at using a PCB Electromagnetic Scanning System! One of the advertised uses for these test devices is for quickly comparing EMC performance when component changes are made etc.! I believe there are 4 different manufacturers who make these devices. The one that I'm just starting to learn about is made by EMSCAN in Canada. Their web is www.emscan.com Maybe someone who has uses one of these scanners can provide an experienced viewpoint? Regards Tony Colorado --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Component Qualification
Group, Can anyone advice on any guide for checking/qualifying second source component, such as crystal, oscillator ferrite bead, mounted on product is still meeting the emission limits? We are manufacturer of pheripherals cards. Some card has crystal and/or oscillator for digital circuitry. Ferrite bead are used too. As these component will affect the final product EMI level, therefore some qualification/guide in terms of EMI must be considered when qualifying second source component. These components are used in lots of product that we made, it would be costly to perform scan for every model. Every product are tested and pass EMI with initial source components. Can we just made a comparison of the specification of the first source compnent with this second source? If yes, what are the crucial specs/information that must meet the first source component? For crystal/oscillator, beside the Frequency stability tolerance specs, what other item is crucial. For Ferrite bead, impedance curve, what other item is crucial. If happens that some specs are slightly out, e.g. 2nd source crystal are having 5PPM more than initla source crystal, Can we make use of the product passing margin, say 3dB, and do some calculation to confidently say that the second source component on the card is still EMI compliance. Likewise for oscillator and ferrite bead. If yes, could you advice on an example of such calculation. Many thanks in advance for the replies. Regards Koh --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
