AM transmissions obviously have different amplitudes when modulated than when not. Above 1 GHz, where transmissions are primarily digitally encoded (phase/frequency shift modulation techniques where the amplitude is constant), I don’t believe this is the case. So it may be that above (for instance) 1 GHz, the IEC formula of adding the modulation depth to the cw limit (i.e,, 10 V/m limit modulated at 80% becomes 18 V/m peak of the modulation envelope) ought to look more like mil and aerospace practice where the limit is the limit.
Just to stir the pot, it isn’t obvious to me (with a largely mil and aerospace background) why the IEC took this approach. Granted AM is AM, but why not simply specify a limit and say that the limit is measured as the peak of the modulation envelope? Assuming that say 10 V/m cw is desired, the limit is then expressed as 18 V/m (or 20 V/m to use round numbers). -- Ken Javor (256) 650-5261 From: Brian Gregory <brian_greg...@netzero.net> Reply-To: Brian Gregory <brian_greg...@netzero.net> Date: Monday, July 24, 2023 at 4:49 PM To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Woodgate's reply on residential Immunity field strength The reference for 20 V/m to EV chargers comes from UL 2231-2. This is not a medical standard, but Annex A does call out the medical standard 60601-1-2 as a reference, as well as CENELEC 50204. We can't figure out why; cell phones produce less than half that, and our WiFi transmitter is probably representative, and is rated well under 1 W. I could see a higher immunity standard as needed for commercial environments, say in a bank of 4-5 chargers. Following along in 61000-4-3, we agree with John that residential applications are clearly best matched to the definition for Class 2 environment, and the table in Clause 5 says the limits for Class 2 equipment is 3 V/m. 20 V/m does not show up in Clause 5 of 61000-4-3 for any class. So, I've should to reach out to a UL standards group and find out if this is really necessary for residential applications. Our local lab can't do more than 10, and an overseas affiliated lab is similarly limited. I'd like to know were this requirement comes from. This is more a question for EV Charging safety than a mainstream EMC question. As a backup, I could request a comment to Ken's point is if they define the peak of the modulation as 20 V/m. I don't know where these are defined. Thanks for all the detailed replies! Colorado Brian 720-450-4933 ---------- Original Message ---------- From: John Woodgate <j...@woodjohn.uk> To: Brian Gregory <brian_greg...@netzero.net> Subject: Re: [PSES] Immunity test field strength, residential setting Date: Fri, 21 Jul 2023 18:05:59 +0100 61000-4-3 is a Basic Standard. It does not specify test levels but indicates possible test levels. You need to look in detail at Clause 5, but look at these words: Product committees shall select the appropriate test level for each frequency range needing to be tested as well as the frequency ranges. The residential environment is usually designated Class 2 (see Annex E of the standard), which calls for 3 V/m. ====================================================================================== Best wishes John Woodgate OOO-Own Opinions Only www.woodjohn.uk Rayleigh, Essex UK I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC) On 2023-07-21 17:44, Brian Gregory wrote: Hello colleagues, We are building EV Chargers for residential markets (not just US) and one of the safety applicable standards is UL 2231-2. It calls out IEC 61000-4-3 for immunity testing parameters, which states a requirement for a field strength of 20V/m. Our EMC expert says typically testing is "done at 3 Vrms, which is standard for most products in residential environments." He can only test up to 10V, and we're hearing the same from an overseas lab to whom our manufacturer refers. Does FCC Part B have guidelines for field strength we can cite? Can some offer this "DC guy" (aka, 60 Hz) a quick definition of what the 20V/m represents? I'm guessing 20 V/m is for higher density commercial applications, aka charging stations, so we probably need an exception for residential. Thank you! Colorado Brian 720-450-4933 This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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