Ken:
Analog meters are inherently good low pass filters and will mask any high
frequency components. The same is truefor most DMMs unless they have been
specified for higher frequencies. Typically, don't expect much accuracy
beyond 100Khz for soem of the best DMMs.
You can always use a scope with adequate bandwidth if you susepct high
frequency conducted components. That way, you can not only identify whether
noise is present but its waveshape. Any changes to make to reduce the noise
are readily visible.
RF power meterssuffer from the same deficiency unless specifically rated and
designed for pulsed waveform measurments. I recall an evaluation done my our
Dept of National Defence that found many gross errors in instruments not
designed or compensated for narrow pulses.
As mentioned on this forum, check for a true rms voltmeter function and
assure yourself what kind of accuracy you're getting at the highest
frequencies of interest. If you can live with 5-10% error - go for it.
Ralph Cameron
EMC Consultant and Suppression of Consumer Electronic Equipment
( After sale)
----- Original Message -----
From: "Matsuda, Ken" <matsu...@curtisinst.com>
To: <emc-p...@majordomo.ieee.org>
Sent: Tuesday, October 03, 2000 3:44 PM
Subject: Leakage Current Measurements
>
> I found something interesting today. While measuring leakage current with
a
> digital multimeter, I noticed a high amount of leakage. The unit
> incorporates a switching power supply, with some EMI/EMC circuitry.
Anyhow,
> I read somewhere that DMMs are some times inaccurate with high frequency
> line conducted emissions. Took a old Simpson analog meter (took forever
to
> figure it out, since I've never touched a analog meter hehehe) and found
> measurements that were rather low. The questions is, I'm wondering if UL
or
> for that matter, any other testing agency actually know about this fact,
or
> merely fail their clients with incorrect data.
>
>
> Any input on this subject would be appreciated.
>
>
>
> Ken
>
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