Derek: When a test lab is engaged to perform testing on a product, the test lab owes the client, at the minimum, accurate test data. However, it is not the “chamber” that delivers that assurance of quality workmanship, rather it is the EMC Engineer in charge of that facility. When the client walks in the door, he expects a knowledgeable testing operation, not an environment that seems to be learning as they go. Not recognizing Ambient noise polluting the Operational emission data is a failure to deliver the expected professional level of competence. To me, it seems pretty clear that the testing lab is at fault. If the problem was rapidly recognized by them, and a new set of data was taken, then the problem is mainly one of embarrassment of the testing lab’s people. However, if it goes on without recognition, if the lab lets the client take his equipment home with the assumption that the equipment has failed, then the longer it goes on, the greater the testing lab’s error and financial responsibility becomes. Perhaps the testing lab never noticed the problem on their own? That would have been a pretty serious indication that the testing lab just wasn’t ready to deliver professional quality testing services.
Another interesting comment was that there was difficulty in “setting up” the test specimen and its support equipment. A good test lab will know what a customer needs to supply long before the test date. Time should be budgeted for the setup and trouble-shooting of ancillary devices, and the customer should be warned that home-brew support equipment may cause EMI issues all on their own. A good test lab will make some suggestions about best practices, but alert the customer that it may be necessary to ameliorate support equipment problems before EUT testing can begin, and this may entail additional time and materials needed to make the support equipment quiet or immune enough to allow testing. Further, a good test lab should always expect some set-up problems, and be ready to surmount these with a plentiful junkbox of rolls of aluminum foil, conductive tape, bond straps, shielded boxes, knitted wire mesh, capacitors, inductors, ferrite beads, isolation transformers, sheet metal and a decent assortment of common hand tools. In short, if your customer says his gadget needs an external water chiller, the test lab should have already thought about ground loops, how to get water in and out of the chamber, and have considered what problems a water chiller might induce in the lab’s electrical environment. The test lab’s customer should not feel that the test lab was unprepared to receive him or that the test lab was anything less than expert in integrating the test specimen and support equipment into the test chamber. It would appear that the selected test lab was just not ready for prime time. Ed Price WB6WSN Chula Vista, CA USA From: DEREK WALTON [mailto:[email protected]] Sent: Wednesday, April 17, 2019 12:08 PM To: [email protected] Subject: Re: [PSES] Question re: Measuring a signal in a noisy environment Interesting discussion, not surprising I have a little empathy, and a whole slew of disagreement with both Ken and Ghery ( both Chaps I have a lot of respect for ) on this one. How best to respond is the question? Cheers, Derek Walton. On Apr 17, 2019, at 1:12 PM, Bill Stumpf <[email protected]<mailto:[email protected]>> wrote: Absolutely agree with Ken. Bill Stumpf Lab/Technical Manager D.L.S. Elecronic Systems, Inc. From: Kenneth Wyatt [mailto:[email protected]] Sent: Wednesday, April 17, 2019 12:21 PM To: [email protected]<mailto:[email protected]> Subject: Re: [PSES] Question re: Measuring a signal in a noisy environment Boy, I have heard all sorts of horror stories from clients with knowledgeable EMC backgrounds who have witnessed sloppy, or just plain wrong, procedures used in commercial EMC test labs. In a lot of cases, the technicians operating these tests have limited background in EM theory and poor knowledge of the actual tests they are running and standards the tests are based on. Just because a test lab is assessed per IEC 17025, doesn’t mean much unless they show evidence the documented procedures are actually being followed. Many test labs fail to perform frequent verification tests to confirm the measurement system is accurate and is repeatable from one day to the next. When I worked for HP, we did a daily verification test using an RF generator connected to the antenna cable to ensure the back-end system measured the same as the day before. We also ran comb generator tests frequently. I always suggest to my clients to make their preferred test lab measure a client-owned comb generator prior to any testing in order to ensure the chamber continues to be reasonably consistent before real measurements are taken. It’s also very important to understand the test standards and EUT configurations well enough to ensure the test technician is setting up things correctly. I know of one case where the EUT cabling was configured wrong and their client repeatedly had emissions failures over weeks of retesting until the correct configuration was pointed out in the standard. Taking photos of the test setup is very important for day to day test consistency. A difference in one cable position can completely throw off repeatability and thus, mislead any troubleshooting efforts. What about ESD simulators? When was it verified last? Does the test lab even have the means to verify the correct tip voltage and pulse characteristics? Is all the measurement equipment calibrated and cal tags current? I could go on… My colleague, Ghery Pettit wrote a recent blog on the subject for Interference Technology: https://interferencetechnology.com/emc-laboratory-selection-audit-items/ Cheers, Ken _______________________ I'm here to help you succeed! Feel free to call or email with any questions related to EMC or EMI troubleshooting - at no obligation. I'm always happy to help! Kenneth Wyatt Wyatt Technical Services LLC 56 Aspen Dr. Woodland Park, CO 80863 Phone: (719) 310-5418 Web Site<http://www.emc-seminars.com/> | Blog<https://design-4-emc.com/> The EMC Blog (EDN)<https://www.edn.com/electronics-blogs/4376432/The-EMC-Blog> Subscribe to Newsletter<http://www.emc-seminars.com/Newsletter/Newsletter.html> Connect with me on LinkedIn<https://www.linkedin.com/in/kennethwyatt/> On Apr 17, 2019, at 10:46 AM, Grasso, Charles <[email protected]<mailto:[email protected]>> wrote: To those wondering what the background and conclusion to that question was: Background: Our testing was performed in a newly minted chamber so proper EMC installation of our product was challenging. Effect: Ingress of high levels of external bb noise. Result: Proper install eliminated the external noise and now the system passed. Concern: While I accept that proper installation and operation of our system is our responsibility, I had expected that the tester would point to the excessive ambient and indicate that our data may not be valid. An inexperienced customer would have left thinking that their product had failed. Am I wrong? Thanks! Charles Grasso W: 303-706-5467 - - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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