RMS voltage of a square wave

No Phyllis, you're the only one who's perfect in this conversation. Perfect asshole, but perfect none the less.

Try reading it. ...only three words and an inequality,

You're wrong, as usual.

The only point you have is between your shoulders, Phyllis.

You're as wrong as Dimbulb, Dimwit.

--
Keith

----------- If it is not sampling- then what is it? Thermal? There is a little black box in the device which is just that- a little black box. I presently have problems getting the applicable pdf from the Analog device site.

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Don Kelly dhky@shawcross.ca
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"Don Kelly"

** Analog Devices have been supplying " true rms to DC converter " ICs for about 30 years.

The data sheet for the AD636 will give you some idea how it computes the DC value of an AC input.

Use Google for more info.

Don't be so damn lazy.

..... Phil

I worked on some true RMS panel meters many years ago, and they used a heater and a thermocouple inside a glass bulb. There was a considerable time delay to get an accurate measurement, and there was some ambient temperature compensation required, but it was very accurate and worked at DC to RF (at least to several MHz). But these sensors were rather expensive and fragile.

A friend and I tried to design a true RMS meter using a lamp and a photocell, but we found that there was a considerable aging effect on the output of the lamp, and there was also some ambient temperature error that needed compensation. I think we were finally able to solve the stability and aging problems by using two lamp/photocell pairs in a sort of bridge circuit, where one was driven by the measured signal and the other was driven by a DC signal that also drove the meter. But the current draw for both elements was more than the allowed specification, as it was a self-contained meter with a range of about 4-8 VRMS.

For a bench instrument, such a method would be very practical. You just need to make two well-matched lamp/photocell pairs, and some signal conditioning, amplification, and limiting for the lamp, and then use an op-amp or other means to drive the other sensor so that the photocell outputs are identical. Then the DC current in the DC sensor matches the true-RMS current in the other, for any waveform or frequency. But it does have a rather narrow range of operation. You can't get very close to zero. Probably 20% to 100% would be possible. The lamp must be driven hard enough to become incandescent and be sensed by the photocell, which has a limited spectral range. The heater/thermocouple could go lower, but becomes relatively insensitive, because heat is proportional to I^2.

Paul

rate-

is

I've got an old AD catalog with "little black boxes" in it. From what I remember the cat has precision instumentation amps, log converters and ???. If you have a part number, I'll see if it's in there. bg

The RMS voltage of a true and symtrical square wave is just the voltage from ground of the "top" of the wave.

A "true RMS" meter will measure this accurately.

However, most AC voltmeters don't respond to true RMS but something else like "average of absolute voltage" or "peak". They are calibrated in RMS using the assumption that the wave form is a sine wave.

** Posted from **

The data sheet that you reference tells how the device is made- with two black boxes-the squarer/divider and the current mirror. It does not explain what each of these components actually do. So -no new information. As I said, the pdf reference at Analog devices doesn't come through completely- just a few lines on a few pages -enough to hint and tantalise but not enough to be of use. It's not for lack of trying for information.

What I wanted to know was what was in these boxes in broad terms of their terms of their operation as there are several ways to get a true rms measurement (assuming component frequencies outside the meter's bandwidth can be ignored).

If you don't know, say so.

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer

"Don Kelly" "Phil Allison"

** So you missed the schematic in figure 9 entirely ???

Wanker.

** Bollocks.

It is all new information in relation to your original *dumb* question - wanker.

**The data sheet for the AD536 has more detail plus quotes the maths formulae device operation relies on:

See fig. 9 again and the text around it headed:

" AD536A Principle of Operation ".

Then f*ck off.

...... Phil

That's for an "alternate on and off" square wave, where one of the two voltage levels is zero.

More often, though, when someone says "square wave", they mean an AC square wave with no DC component, and two voltage levels +V and -V that are symmetric about zero. For *that* square wave, rms voltage is equal to peak voltage.

Dave

Don Kelly wrote: [...]

The 'cover' PDF gives a fairly clear and thorough description of how the RMS-DC convertor is designed, down to the level of a few basic functional blocks.

Did you expect others to do your homework for you?

** The link I originally supplied him for the AD636 has a full description of how the device operates INCLUDING a detailed internal schematic.

See the section starting on page 5, " AD636 Principle of Operation ".

** The fool cannot see what is right in front of his eyes.

Usual disability of all wankers.

...... Phil

He obviously did not get the entire document, for whatever technical reason. Therefore, he didn't see the other information. Since you apparently don't frequent this newsgroup, you might want to do some homework yourself before you direct comments like that at an engineer who can run circles around you in terms of his electrical knowledge.

--
Benjamin D Miller, PE
www.bmillerengineering.com

** Try following the thread - pal.

All the info was in the FIRST link I supplied( to the AD636) and he could see ALL of that.

** BOLLOCKS !

** Shame how you cannot even follow a simple thread - let alone see through that arrogant fake Kelly.

..... Phil

----------- Yes- I only got the first page -hence the question. Now I have the full pdf and see the process.

Thank you for your "courteous" response.

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Don Kelly dhky@shawcross.ca
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----------------------------

He must like you. He didn't even use the word 'festering'!

From reading this thread, and having conversed with Don on this group over the past several years, it is easy to see who is the arrogant, foul-mouthed, whiner, and who is a courteous, sincere individual.

daestrom

"daestrom"

** Pathetic wanker.

... Phil