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 <klauskvik@hotmail.com>
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: <v5n4vn$3g81l$1@dont-email.me>
References: <v5kq09$2ul7i$1@dont-email.me> <v5llmg$37ib5$1@dont-email.me>
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: <v5llmg$37ib5$1@dont-email.me>
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.