Re: Problems with "true" RMS Readings

["Jim Lux" <jimlux-at-xxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

A good test of "true" rms meters is a resistive load driven by an SCR/Triac
dimmer.  As you vary the phase angle, the peak/rms/average ratios all
change. A scope can give you the conduction angle, from which one can
compute the expected numbers.

 And, if you've got a good lightmeter, you can actually do a thermal RMS
measurement by comparing against DC.  This IS, of course, the most accurate
way to measure power and is used for wideband RF, microwave, etc, in a
so-called Type IV Power Meter.  It can literally work "DC to light", with
proper calibration and compensation for reflected power.

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> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Problems with "true" RMS Readings 
> Date: Wednesday, November 01, 2000 6:45 PM
> 
> Original poster: "harvey norris" <harvich-at-yahoo-dot-com> 
> 
> I recently purchased Radio Shack's Auto Ranging LCD
> Digital Meter. This meter additionally has the quality
> of reading the "true rms". All normal digital meters
> have this rms reading also, and I have used Radio
> Shack meters for years with no problems. But this one
> is giving me a real headache Perhaps it is defective
> but for now I can only ask for a replacement, but I
> have a feeling that it will do the same thing. First
> let me refer to the manuals explanation;
>