Path: ...!npeer.as286.net!npeer-ng0.as286.net!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Klaus Vestergaard Kragelund Newsgroups: sci.electronics.design Subject: Re: Estimation of magnetic field strength of radiated immunity test Date: Fri, 28 Jun 2024 22:04:10 +0200 Organization: A noiseless patient Spider Lines: 53 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Fri, 28 Jun 2024 22:04:08 +0200 (CEST) Injection-Info: dont-email.me; posting-host="216c6608db706ffbda0101e115d81a73"; logging-data="3678261"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19osGygJhWEKe59QKjp6pPzIXfgWoedDpQ=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:96T9QiasQika6aDKXMyT2emLdG0= Content-Language: en-US In-Reply-To: Bytes: 3619 On 28-06-2024 08:37, John R Walliker wrote: > On 27/06/2024 23:44, Klaus Vestergaard Kragelund wrote: >> Hi >> >> Normally when testing a product for radiated immunity one would apply >> a field of 10V/m at a distance of 3m, to determine if the product is >> susceptible to external incoming radiated fields. >> >> In my specific case, we have a 3MW converter which has quite high >> internal fields, so I am doing an alternative test. >> >> In this test, I have measured the magnetic field at a certain point in >> the cabinet next to the sub-block I am working on. That way I know the >> magnetic field at this point, and the idea is then when we need to go >> to the approval body to test radiated immunity, that we will set the >> level of the antenna to match the recorded level next to the sub-block. >> >> Specifically I have used a near field probe to and measured a H field >> of 30A/m at this sub-block at 1MHz. >> >> The near field probe voltage was recorded with a scope and in my lab I >> wound a coil and ran a 1MHz signal through the coil until I got the >> same level, then calculated the field with H = Iapplied*nturns/coilheight >> >> In the approvals test, the antenna is 3m away. Normally they use a >> level of 10V/m and for far field approximation using 377ohm, the H >> field from the antenna is H = 10V/m / 377ohm = 0.03A/m. >> >> At 1MHz, the wavelength is far above 3m, so the antenna will be in the >> near field, so the resistance is 60ohms, and the field decays with >> 1/r^2 distance since it's close to a magnetic field. >> >> Anyway, it seems the field needed at the antenna for this test would >> be VERY large to generate H field of 30A/m 3meter from the antenna. >> >> How do I calculate that level and any inputs into if my reasoning >> above is correct? >> >> I know that when you move into the near field, it's hard to predict >> the far field level, but in this case is seems since I am operating at >> 1MHz that both the antenna and DUT is in the near field... >> >> Thanks >> >> Klaus > > Why are you testing at 1MHz when radiated immunity testing is normally > only done at frequencies higher than 80MHz? > Correct, radiated immunity is from 80MHz to 6GHz. We know that the field, 10V/m is smaller than the internal EMC. So we detect the largest possible disturbing signal frequencies, and replicate the EMC test, monitoring the performance of the DUT.