Because the field around the EUT is heavily distorted during the test. It might work for small EUT.
THE best method is calibration without EUT using a field probe, and monitoring forward power during radiation of the EUT. If you are worried about the antenna, monitor the reflected power also. If that deviates SUBSTANTIALLY , you have a problem. Small deviations are to be expected due to the properties of your room changing when EUT is in place. (think close field coupling between EUT and antenna!!!) A field probe can also be used, but should NOT be used to adjust levels. Alternately, if you use the same antenna as during receive, do a check on receive quality using a small portable reference source (also before installing EUT as EUT will have impact on the transfer) . If the result is within a defined margin the measurement chain is OK. We have a small dipole installed at the back of the room (behind EUT) and verify the transfer from that antenna (connected to a generator) to the measuring receiver at a number of frequencies before each emission measurement and before each immunity measurement. Antenna, receiver and amplifier are automatically coupled using coaxial switches so it’s a fast procedure. If the majority of the frequencies received are within a certain margin (+/- 2dB ) the receive chain (and so the transmit chain) is OK. Better accuracy cannot be obtained, unless the EUT is removed. Even worse, at some frequencies EUT radiates , or the transfer is influenced by the EUT metal work / cabling. That is why we use a number of frequencies, and no they are of course not related harmonically, nor popular clock frequencies. We also use the procedure to verify proper antenna orientation. The results are logged with each measurement and in a generic log file. As we write our own test software that was not a big deal. Regards, Ing. Gert Gremmen, BSc [email protected] <mailto:[email protected]> www.cetest.nl Kiotoweg 363 3047 BG Rotterdam T 31(0)104152426 F 31(0)104154953 Before printing, think about the environment. Van: [email protected] [mailto:[email protected]] Namens Gärdin Petter Verzonden: Wednesday, September 28, 2011 5:14 PM Aan: [email protected] Onderwerp: RE: [PSES] BS EN61000-4-3 and calibrated fields. According to the standard, 8.2 Execution of the test … Before testing the intensity of the calibrated field strength should be checked to verify that the test equipment/system is operating properly. … It says should, and the easiest way is to check field strength is with a field probe, so why not use it during the whole test to make sure nothing goes wrong during testing. It's usually much more expensive to rerun test than to make sure you do it correctly. Petter From: Grasso, Charles [mailto:[email protected]] Sent: den 28 september 2011 17:00 To: [email protected] Subject: Re: [PSES] BS EN61000-4-3 and calibrated fields. But is that REQUIRED in 61000-4-3? Best Regards Charles Grasso Compliance Engineer Echostar Communications (w) 303-706-5467 (c) 303-204-2974 (t) [email protected] <mailto:[email protected]> (e) [email protected] <mailto:[email protected]> (e2) [email protected] <mailto:[email protected]> From: [email protected] [mailto:[email protected]] On Behalf Of ce-test, qualified testing bv - Gert Gremmen Sent: Wednesday, September 28, 2011 12:30 AM To: Brent G DeWitt; Kunde, Brian; [email protected] Subject: RE: [PSES] BS EN61000-4-3 and calibrated fields. EUT has big impact on local field. Field NEEDS to be leveled without EUT. Regards, Ing. Gert Gremmen, BSc [email protected] www.cetest.nl Kiotoweg 363 3047 BG Rotterdam T 31(0)104152426 F 31(0)104154953 Before printing, think about the environment. Van: [email protected] [mailto:[email protected]] Namens Brent G DeWitt Verzonden: Wednesday, September 28, 2011 1:21 AM Aan: 'Kunde, Brian'; [email protected] Onderwerp: RE: [PSES] BS EN61000-4-3 and calibrated fields. We have done this at several labs I work for, but it was always just a sanity check to make sure that neither the amplifier nor cables to the antenna had failed. It is totally useless as a function for leveling for commercial immunity measurements. Best regards Brent From: Kunde, Brian [mailto:[email protected]] Sent: Tuesday, September 27, 2011 8:19 PM To: [email protected] Subject: Re: [PSES] BS EN61000-4-3 and calibrated fields. Not to hijack this thread, but why do some test labs setup the Field Probe in the chamber next to the EUT during the test? The measurement with the EUT in the field should be all over the place and would have little value. Am I missing something or are some labs leveling off the Field Probe during testing? From: [email protected] [mailto:[email protected]] On Behalf Of Ian White (UK) Sent: Tuesday, September 27, 2011 6:00 AM To: IEEE Forum ([email protected]) Subject: BS EN61000-4-3 and calibrated fields. Could you please help: Could you explain what is the correct procedure when using an anechoic chamber which is calibrated and operating to EN61000-4-3. During calibration of the chamber, a calibration file is made and it is assessed according to the guidelines laid down under BS EN61000-4-3. During calibration the chamber is empty. During a normal test run a UUT is put into the chamber. The questions is : a) Do you use the calibration file as the starting point and adjust the field strength which may have changed due to the UUT being in the chamber. b) Just take the calibration file and run it and except the filed strengths would have changed due to the UUT being in the chamber. Thanks Ian White Compliance and Reliability. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> ________________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. 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