RMS voltage of a square wave

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"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:
http://www.farnell.com/datasheets/57860.pdf
See fig. 9 again and the text around it headed:
" AD536A Principle of Operation ".
Then fuck off.
...... Phil
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----------- 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.
--

Don Kelly snipped-for-privacy@shawcross.ca
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<snip>
He must like you. He didn't even use the word 'festering'!
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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?
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"D. Ismay"

** The link I originally supplied him for the AD636 has a full description of how the device operates INCLUDING a detailed internal schematic.
http://www.farnell.com/datasheets/57885.pdf
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
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D. Ismay wrote:

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
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"Ben Miller"

** 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
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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.
<plonk>
daestrom
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"daestrom"

** Pathetic wanker.
... Phil
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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
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says...

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
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snipped-for-privacy@tpg.com.au says...

Slick, though not perfect.

Normally <> is not
It *is* used, though perhaps not in handheld DVMs. IT is used in Kill-a-Watts.

How do you get better than 1% accuracy on a scope? Sampling works to any accuracy one desires and can go fairly high in frequency. Even higher if the waveform is repetitive.
--
Keith

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"krw" Phil Allison "Don Kelly"

** Err - so just like you ?

** ?????

** Bollocks .

** You are not paying attention to the point at issue - fuckwit.
BTW:
Fix your stupid settings so the name of the poster you arr replying to is left visible.
...... Phil
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snipped-for-privacy@tpg.com.au says...

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

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*PROVIDED* you measured that voltage with a true RMS voltmeter, then yes, you have the true RMS current. But typical voltmeters are not true RMS devices. So beware, "Garbage In / Garbage Out"
daestrom
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"daestrom"

** It ain't that simple.
The vast majority of so called " true rms " AC ranges fitted to DMMs are of very limited bandwidth - typically 30Hz to 1kHz within 1% accuracy, a few more expensive examples go to 20 kHz or even 100kHz.
So, unless the voltage wave under test falls within the particular meter's bandwidth, the reading will be in error and likely very seriously so.
..... Phil
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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.
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