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Simple circuit measures RMS value of AC power line

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re: Simple circuit measures RMS value of AC power line
hithesh   11/10/2012 10:47:06 AM
I actually thought this article would explain how you get RMS output from AC. Nothing useful in this article.

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re: Simple circuit measures RMS value of AC power line
grouts   11/9/2012 5:22:08 PM
The above circuit and thesis is reasonably OK. A couple of things not included in the above engineering are: - loss of course in the line/circuitry leading to the above measuring circuitry, including to the two resistors. - The thermo properties of the two resistors being heated by the signal-under-test and the DC signal. You have to, of course, also include the TRANSIENT thermo properties of both (I never did trust DC, including the wiring to/from the power supply.) By the way, I believe your above circuit, including it basic premise, is covered by a patent taken out by Norm Dillman while at HP. Myself, I used similar circuit approaches as this to provide thermal biasing stability on the many class B power amplifiers I designed for GE Audio Products back in the 60's. But you have a nice circuit as well as a nice paper describing it and your engineering. --Steve Grout

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