Voltmeter Question

[bgavin]

Ditto for SNOPES

[Gregory East]

So if I'm understanding it properly ....

Umm... Wikipaedia is not the smartest authority in the world!

So what are you trying to say?
Have I been duped by wikipedia or are all the guys buying "true RMS" meters to set up their pa just wasting money?

[cjd]

So what are you trying to say?
Have I been duped by wikipedia or are all the guys buying "true RMS" meters to set up their pa just wasting money?

The other meter will give the right answer only under certain conditions. if you inadvertently fail to meet those conditions you may get the wrong answer and never know it (unless maybe your gear gets toasted). So the true RMS meter is safer because it is more accurate under a wider range of conditions. IMHO, definitely worth the money.

[Harley]

Have I been duped by wikipedia

Wikipaedia, as I understand it, has all and sundry contributing to it. It's a live encyclopaedia. That means someone can post some there and you'd be none the wiser.

I liken Wikipaedia to the committe who designed a horse - which you and I would call a camel.

[Gregory East]

So what are you trying to say?
Have I been duped by wikipedia or are all the guys buying "true RMS" meters to set up their pa just wasting money?

The other meter will give the right answer only under certain conditions. if you inadvertently fail to meet those conditions you may get the wrong answer and never know it (unless maybe your gear gets toasted). So the true RMS meter is safer because it is more accurate under a wider range of conditions. IMHO, definitely worth the money.

What conditions?

A sinewave from a PC signal generator is the perfect match to the "rough enough RMS" meter as I understand it. It assumes the input is a perfect sine whereas the "true" one actually measures the signal and computes it. Or wikipedia is telling lies?

[Sydney]

How about a simple test?
Those with True RMS meters compare voltages of clean sine waves
at relevant frequencies to those not advertised as such.

[Ron K]

http://enginova.com/true_rms_volts.htm

A pretty good real world explanation of whats really going on.

[Sydney]

Very interesting...
I have being in PM mode w a forum member about this article and the math behind it.

( A couple of links in the Ed section fully explain - as Ron said "What's going on" )

[Gregory East]

What's root mean square again? I thought it was the mean of a rendering A/C into two +ve waves

ie the mean of the square root of squared voltage.

Anyways, bugger square waves, we're not talking about clipped signals. Sydney had the best suggestion in comparing the measurement of a pure sine signal between high falutin' and bargain bin meters.

[Sydney]

On a related note:
AudioXpress 7/09 has a True RMS Audio AC Voltmeter construction article using the Analog Devices AD636JH True RMS to DC Converter.
The data sheet notes the formulas behind the transfer function involved.

[thijs666]

So if I'm understanding it properly a true rms meter is total overkill. They're ALL rms but assume the signal is approximately sinusoidal so feeding a true sinewave gives the exact same result as a flash one with the fancy computer. DOH.

That is what I was trying to say. But you MUST KNOW what/how you are measuring. Sydney is wright in saying a true RMS meter is safer for the 'puppies' . But since I use sine waves generated with my DDX3216 oscillator, I'm not interested in an expensive true RMS meter (although it would be a nice supplement in my measuring equipment ).

[Sydney]

The Analog Devices AD636JH is only $10 and compared favorably to the HP 3478A used in the article.
Looks like a simple build ( for someone of your skill set )