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Comparing accuracy of true RMS meter with Averaging type and waveform quality

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Lightages:
I am working on a number of things right now and I have been trying to compare the accuracy of reading between two meters, one with true RMS and one without. My question is; What is the effect of sine wave distortion on the accuracy of the averaging type meter? In other words, if I have a sine wave with let's say 0.7% total distortion, what would be the effect in % accuracy on the reading of this meter?

I suspect that at this level of distortion that the effect would be almost nil.

jahonen:
I think that i depends how much the crest factor will change, there is not single answer for given distortion. But for small distortion figures, I also guess that the effect is quite "small". IIRC, even for square wave, the reading will be off "only" by 11%.

Regards,
Janne

Zero999:
The best method to test a true RMS meter is to measure a squarewave with 50% duty cycle with a fast rise/fall time: the RMS voltage should be equal to V/sqrt(2). A 5V squarewave should read 3.536V. You could use a CD4060 oscillator/counter run off a 5V regulator to get a squarewave with a duty cycle of exactly 50%.

Bored@Work:

--- Quote from: Hero999 on October 01, 2011, 05:59:17 pm ---The best method to test a true RMS meter is to measure a squarewave with 50% duty cycle with a fast rise/fall time: the RMS voltage should be equal to V/sqrt(2).

--- End quote ---

Of course not. V/sqrt(2) is the formula for sinusoidal voltages only.

--- Quote ---A 5V squarewave should read 3.536V.

--- End quote ---

A 5 V peak-to-peak square wave should read 2.5V.

vk6zgo:
Yes,an averaging meter scaled to read as RMS will read 3.5356 volts--or at least,an analog one will try to!(probably readable to 3.5!)
I'm not altogether sure if the relationship stays correct with an averaging DMM for a square wave--never tried it.
Usually use an Oscilloscope,+ a HP22s--or guess! ;D
VK6ZGO