When at a small company, I once built a couple of LISNs and used anti-parallel, standard recovery 1A diodes attached across BNC output. (after blasting the attenuator on an HP8591 on a transient on day) Never had another failure after adding the diodes. _____________________________________________________________________________________
Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Regulatory Compliance Engineering From: "ce-test, qualified testing bv - Gert Gremmen" <g.grem...@cetest.nl> To: EMC-PSTC@LISTSERV.IEEE.ORG Date: 12/27/2011 11:09 AM Subject: Re: [PSES] Protect An EMI Receiver Because EUT may contain inductors and switches that generate spike when intentional or unintentional switching or switching ON/OFF during the test. Invariably the day comes that a BIG transient blows BIG money without such a protector. Gert Van: emc-p...@ieee.org [mailto:emc-p...@ieee.org] Namens Ken Javor Verzonden: dinsdag 27 december 2011 19:03 Aan: Untitled Onderwerp: Re: Protect An EMI Receiver Gert provided an excellent post, but I am puzzled by the need for all this protection. Granted I work in a screen room with either dedicated power or filtered power, but here is the question, nonetheless. The conducted emission limit above 150 kHz is at or above 60 dBuV these days, correct? So 30 - 40 dB of either internal or external broadband attenuation is available for use, while still providing a suitable noise floor for a typical ESU receiver, and that’s without using the pre-amplifier. Further, in the case of the original post, preselection exists filtering out the noise below 150 kHz. Why is there even a problem? Ken Javor Phone: (256) 650-5261 From: "ce-test, qualified testing bv - Gert Gremmen" <g.grem...@cetest.nl> Date: Tue, 27 Dec 2011 18:26:50 +0100 To: <emc-p...@ieee.org> Conversation: Protect An EMI Receiver Subject: RE: Protect An EMI Receiver Happy new year to all, and hope you had a great Christmas ! Every receiver or spectrum analyzer used for conducted measurements on a LISN or AMN to mains voltage ABSOLUTELY NEEDS a dedicated surge/spike suppressor. They are easy to purchase, but you can build one yourself using a fast bidirectional 10V transient suppressor with low capacitance when 0 Vdc over it (use your cap meter of read datasheet) If the suppressor was mounted in a 50 ohm circuit you would have problems with high frequencies, but if you connect this suppressor parallel to the ground resistor in a 20 dB T-type (NOT PI) attenuator the performance is much better. The attenuator adds 20 dB to the impulses and the transient suppressor cuts off everything above 10 V The ground resistor in this configuration is slightly above 10 ohm (instead of 50 Ohm) if I remember well, so the high frequency cut-off is way above 30 MHz. Use old fashioned coal resistors or smd film resistors (3 in series per value) and mount in a small coaxial enclosure with 2 BNC's. Make sure the input resistor allows for 500V each, unless you live in the USA then 200 V is enough. Voila your home brew transient suppressor with same specs as commercial products. Of course it needs calibration, and possibly adjustments to meet your accreditation requirements. My software (EMI-SCAN) allows for the transfer characteristics (+/- 1dB) to be corrected in real time. Gert Gremmen ce-test qualified testing bv Owner LinkedIn EMC experts group Van: emc-p...@ieee.org [mailto:emc-p...@ieee.org] Namens Grace Lin Verzonden: dinsdag 27 december 2011 17:01 Aan: emc-p...@ieee.org Onderwerp: Protect An EMI Receiver Dear Members, Happy New Year!!! I need your advice to prevent R&S ESU receiver from damage. A service report (as a result of annual calibration) indicates "frequency response out of specification below 10MHz. Adjusted frequency response. Adjusted the reference oscillator to optimize frequency accuracy when operating from an internal standard." Plots from the calibration report shows the problem frequncy range was right below 150 kHz (100 kHz -150 kHz). I wonder the problem was caused by click noise from dimmers. Under receiver mode, I was unable to see the click noise (below 1 MHz in most cases) displyed in the ESU screen when the start freq was 150kHz and stop freq was 30MHz. I was able to see the high click noise when the receiver was set at the certain frequency (for example 150 kHz). At the same time, the screen also showed IF Overload message. What should I do to prevent it from happening again? 1. Is there any way to play with the ESU's preselection? ESU has 13 preselection filters ( http://www.rohde-schwarz.us/en/products/test_and_measurement/emc_field_strength/ESU-%7C-Overview-%7C-100-%7C-6430.html). The first one covers 20 Hz to 150 kHz and the second one covers 150 kHz to 2 MHz. I thought when I take data starting 150kHz, the emission below 150kHz shouldn't be selected (not cause the problem). 2. Should I find a filter to bypass the emissions below 150kHz? If yes, could you please refer me one? 3. Should I find an attenuator to attenuate the emission below 150kHz? If yes, could you please refer me one? Thank you very much for your time and look forward to your advice. Best regards, Grace Lin - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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