RMS Voltmeter

Who said that!?

Reply to
Long Hair
Loading thread data ...

snip

Well, that decidedly rules you and anything you say out.

You wouldn't know. I am a man. We are a lot of things.

You are a goddamned idiot.

Reply to
Long Hair

You obviously suffer from multiple personality disorder.

You are AlwaysWrong.

Reply to
krw

If the front panel of the DMM says "True RMS" there's a fair chance that it might be a true RMS meter. Neither meter you mention is true RMS.

APC Back-UPS or SmartUPS? With no load, the Back-UPS series produces a step approximation of a sine wave while the SmartUPS produces a fairly low distortion sine wave with no steps. However, put a reactive load on a Back-UPS, and the waveforms are really ugly: So, what are you trying to demonstrate or test by using AC power? True RMS will not produce any sane numbers with all that garbage on the waveform. I suggest using a function generator to test DVM's, not

117VAC or UPS power.

Here's a Dave Jones review of a few $100 digital multimeters, most of which are true RMA. Start at 40:30 for his version of the true RMS test using a triangular wave at various frequencies: The highlight of the video is Dave dropping and bouncing each DVM. It's near the end.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

-----------------------

** Wot - only a "fair chance" ??

** I agree that if it does not say so, it isn't.

Having a "true RMS" converter IC for the AC ranges is a mark of distinction for portable DMMs that makers and vendors are not likely to hide.

** The cleanest of those Rigol screen captures is close to the ideal output from a ( non sine wave ) UPS. I say ideal, not typical.

That wave consists of continuous, pi-polar pulses with a 50% duty cycle. Such a wave has the same peak and RMS value as a sine wave.

At 100% duty cycle, it becomes the familiar "square wave" - but then the RMS value becomes the same as the peak and is 41% too high. Incandescent light bulbs would last only seconds.

** Yep - you can compute the "true RMS" value from a scope trace and see how accurate a given meter is over a rage of frequencies.

Prepare to be disappointed with most of the budget hand helds.

.... Phil

Reply to
Phil Allison

Jesus' Half Brother, accoding to some.

--
This email has not been checked by half-arsed antivirus software
Reply to
Jasen Betts

poison."

James 3:8-14 King James Version (KJV)

8 But the tongue can no man tame; it is an unruly evil, full of deadly pois on.
Reply to
Andy

What annoys me are those True RMS meters that are AC coupled. Feed a filament lamp 1V AC sitting on top of 12V DC and it lights with same intensity as 12V but such a meter will measure 1V on the "True RMS AC" range even though the effective/heating volatge is 12.

piglet

Reply to
piglet

I would try an adjustable duty cycle square wave; probably the worst-case test method.

Reply to
Robert Baer

worst-case test method."

That'll only work if the waveform is all posiitive or negative going. If it is centered and has equal amplitude at the positive and negative parts of the cycle the RMS value stays the same and variable duty cycle is meaningle ss.

As I said in the other newsgroup on the crosspost, the easiest way is to co mpare the readings of equal amplitude sine and square waves. A peak reading meter will rad the same, the true RMS meter will read lower on the sine wa ve. It should read 0.7071 * pesk voltage, but all the peak voltage om the s quare wave. Thus far nobody has come up with an easier test that is at leas t as conclusive as that one. Yours included. Where do you easily get variab le duty cycle waves anyway ? You have to build a circuit for that. Simple s ine and square is alot easier. An audio amo, resistor and a couple of diode s are all you need along with either a scope or a meter you know is peak re ading and NOT true RMS, which means most of them. Or you could try a light bulb, which is how they did it in the old days.

Reply to
jurb6006

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.