I suppose that average multimeters are just calibrated for sine wave, and not for a real average.
I know what true-rms is, but I wonder if it is required to measure a real audio signal.
With "real" I mean a mix of many frequencies, not just a test pure sine wave.
I suppose an average meter should work fine, but I've got no true-rms to compare.
Would an average and true-rms meters differ in readings?
Thanks!
Sorry MrAl, but you need to stop smoking whatever illegal substance you appear to be using
Normal multimeters read the 'average' calibrated solely for a sinewave - on the assumption that it's going to be used for mains measurements - as it's designed to be.
Obviously measuring a squarewave will be massively incorrect, as it's not calibrated for that.
any idea why the two images above disagree?
I suppose that average multimeters are just calibrated for sine wave, and not for a real average. Maybe that explains what MrAl explained.
Images I was talking about are on Post #18
I know what true-rms is, but I wonder if it is required to measure a real audio signal.
With "real" I mean a mix of many frequencies, not just a test pure sine wave.
I suppose an average meter should work fine, but I've got no true-rms to compare.
Would an average and true-rms meters differ in readings?
Thanks!
Yes, but can you describe ONE such contradiction?
Are we using a "RMS" meter to measure power? or audio?Have a look at this: https://en.wikipedia.org/wiki/VU_meter
The Fluke meter has an AC frequency measurement limit, which may have been the source of your observed large measurement error.
A Fluke 114 true RMS meter, for example, has an upper frequency limit of 1kHz, which would seriously limit its accuracy when trying to measure high frequency signals, such as from a switching power supply.
A fundamental rule is, you have to know the limits of the instruments you are using if you want to make accurate measurements.
The Fluke is indeed a true RMS meter when used within it's specification limits, which you apparently didn't do.
Not necessarily. Know that "true-RMS" doesn't always mean true-RMS. At work, we have a fluke meter labelled a "true-RMS", but it's not. It was giving us weird readings with some special switched LCR waveforms so we compared it to a bench meter power meter and an oscilloscope's calculated RMS values (both devices confirmed to numerically calculate RMS from samples). The bench meter and oscilloscope agreed and the Fluke meter was off by a factor of 0.7.
As asked the guy that owns it and he told us that it "true-RMS" only under certain conditions so it seems that if the waveform strays too far from sinusoid then it's no longer valid since it's working under some set of assumptions rather than numerically calculating the RMS.
He didnt say and we didnt ask. I dont have photos, let alone remember what circuit we were working on.What are the "certain conditions"?
Do you have a scope image of the special switched LCR waveform?
Sure. Simple one:
Top image, the square wave is 10% higher on average than RMS, but on the other, they match.
Isn't it that a contradiction?
Sure. Simple one:
Top image, the square wave is 10% higher on average than RMS, but on the other, they match.
Isn't it that a contradiction?
Take a look herefor Crest Factor limitations.
Bandwidth and high frequency content is your first wall.
Crest factor is your second wall.
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