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non true rms instrument ???

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ahmed osama

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we know the simple cheap Multimeters are not true rms meters which mean it reads only the true rms for the pure single freq. signal..

So my ques. if i have a signal 1Khz 50% duty ,what going to be the voltage reading in this "non true rms meter" "the cheap meters :) "??

and how to simulate it in the simulation programs
 

Hi,
The measurement shall correspond to the amplitude of the fundamental. So it shall be less than the true value. You need to do a fourier analysis of the signal and then filter out the higher frequency components for simulation.
B R M
 

These low cost meters measure either peak or average and do a guess for the RMS based on the assumption that the input is a sine wave.

I know of some types which do a series of random samples and calculate the rms from that. There is an IC that actually heats a resistor with the input signal and then heats another resistor with DC and has a feedback loop to make the two temperatures the same.
 

Hello,
Mechanical (and most of the cheap digital) instruments measure average voltage, and scale display to read 1.11 times this value. In a pure sine wave that is the same than the RMS value.
Best regards
 

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