Is A Fluke 8000a True RMS ?

I always thought that if it is they would say because it is a feature, but it is not mentioned in the manual.

However, with my generator which is pretty accurate on P-P, when I do not d isturb the level, on square I set it to 10 volts and switch to sine it read s something like 6.38.

Seems to indicate that it is, but if so I am sure they would tout it in the manual and all other things relevant to the unit.

If it is peak reading, there would have to be something wrong. I just looke d and the generator is set to about 4,250 Hz.

Is this thing TRMS or not ?

I figured this question better here than in SEB or SER. Half of them people do not understand what TRMS is, let alone to test it. I should NOT see a d ifference in the sine and square if it is not TRMS, correct ?

If it is great, if it isn't that is OK. I like it anyway, like my 8050a whi ch IS TRMS because IO find the red LED display easier to read, especially a t a distance.

I could adopt it or sell it, whaddya think ? I know it is old but I do not care as long as it is accurate. With the 6.37 instead of 707 it could be a bit out of calibration, but I can handle that. My buddy has some standards traceable to the NBS a couple of years ago.

Does I or doesn't I ?

Reply to
jurb6006
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The 8000a uses an opamp precision rectifier to measure the AC value. It is (up to 10KHz) measuring the peak voltage and scaling based on an assumed sinusoidal input.

So, no.

Reply to
PN2222A

** Lotsa stuff is left out of manuals.

** It is a 100% FALSE assumption that any precise connection exists between the amplitude of sine and square outputs on a given signal generator.

** Nope.

** Seems to be YOUR problem too.
** 100% wrong.

** Have a brain ?

..... Phil

Reply to
Phil Allison

Average, not peak.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

** 100% wrong. "

Splain to me then why if the P-P value is the same it reads different. I am not being sarcastic, realy I want to know.

If you think I am off, well of course you do :-), I will stick it back on the bench and hang a scope on the input to see for sure. But the way this generator works is pretty accurate.

I'll retest it and you explain how a peak reading meter rads different on different waveform with the same peak value.

I mean I do not disbelieve you, and as I said it would be mentioned SOMEWHERE, but how does it happen to read different ?

I will recheck it and if the peak value is not the same out my generator I will have mustard and dill relish on my crow, along with a helping of fuckoff and fuckme.

Reply to
jurb6006

OK. On the scope I adjust to exactly 10 volts peak, that it 20 volts P-P. On a square wave it reads 11.50, switched to sine and confirmed at 10 volts peak it reads 7.18.

What explains this ? It does not say "average" reading or anything of the sort so it is logical to assume peak * .707 to get "RMS". Why the discrepancy ?

Reply to
jurb6006

S,

am not being sarcastic, realy I want to know.

the bench and hang a scope on the input to see for sure. But the way this generator works is pretty accurate.

different waveform with the same peak value.

HERE, but how does it happen to read different ?

I will have mustard and dill relish on my crow, along with a helping of fuc koff and fuckme.

RMS was once called EE, electrical equivalent. It means equivalent heating effect for a heater or filament bulb. If the peak voltage is the same for b oth waveforms - which can not be assumed to be so for a sig gen - there is then much more area under the square wave than the sine, so more energy is imparted to the load. Ie the rms voltage is greater for the square wave.

NT

Reply to
tabbypurr

This kind of meter measures average rectified voltage, and multiplies that by 1.111 (0.7071/0.6366) to display the voltage. That makes a sine wave display its RMS voltage.

If it measures the average of a +-10 volt square wave, and multiplies by 1.111, it should display 11.11.

Nobody's perfect. It may not handle the speed of the waveforms very well. What's your frequency?

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

** Q. Why do it that elaborate way?

A. In order to mimic the operation of an analogue AC voltmeter.

Regular moving coil multimeters have AC ranges that diode rectify AC waves before feeding them through the coil. Hence the coil only tries to move in one direction while it's mechanical inertia *averages* out variations in dr ive force, excepting at very low frequencies where the needle will vibrate around the average value.

Since the amplitude of a sine wave has LONG been defined to be its DC equiv alent value (not average), the scale on the meter is adjusted by plus 11% t o eliminate the inherent error - but correct only when reading sine waves.

Interestingly, *moving iron" amp meters have no such problem - the same met er reads both AC ( sine wave or otherwise) and DC currents accurately.

..... Phil

Reply to
Phil Allison

It's starting to sound like the AC readings on most meters are useless, or close to...

???

Reply to
jurb6006

It's not elaborate. It's just a little arithmetic.

The math is the same. An old VOM had a series resistor and a rectifier (copper oxide or germanium) and a DC meter movement. It responded to average voltage so had to be fudged up 11% to indicate the RMS of a sine wave.

You can define the amplitude to be peak, p-p, average, or RMS.

But the price paid is that torque goes as coil current squared, so the scale becomes very nonlinear; some of that can be compensated. And frequency response is very limited. I don't think anyone used a moving iron movement in a general-purpose VOM.

Here's a beautiful old true RMS wideband ammeter.

formatting link

My wife saw it at a non-electronic flea market and bought it for something like $2 and figured that I might like it. It's almost certainly thermocouple based.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

Nowadays lots of DVMs are very good true RMS. But watch the frequency response; low-end meters don't even cover the audio range.

For a complex waveform, only an oscilloscope shows what's there.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

es before feeding them through the coil. Hence the coil only tries to move in one direction while it's mechanical inertia *averages* out variations in drive force, excepting at very low frequencies where the needle will vibra te around the average value.

uivalent value (not average), the scale on the meter is adjusted by plus 11 % to eliminate the inherent error - but correct only when reading sine wave s.

meter reads both AC ( sine wave or otherwise) and DC currents accurately.

in the 1920s that was the norm. Ohms/volt too low for most electronic work, and the use of a metal case as one of the electrical connections was a dan ger.

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NT

Reply to
tabbypurr

** It kinda is.

** The POINT was and is to mimic a standard AC volt meter or multimeter so voltage readings do NOT conflict - no matter what the AC wave.
** You are mindlessly repeating my post.

es before feeding them through the coil. Hence the coil only tries to move in one direction while it's mechanical inertia *averages* out variations in drive force, excepting at very low frequencies where the needle will vibra te around the average value.

uivalent value (not average), the scale on the meter is adjusted by plus 11 % to eliminate the inherent error - but correct only when reading sine wave s.

** Only a moron would try to *re-define* the amplitude of a sine wave as be ing anything other than it's RMS value.
** FFS I know all this, it's how it does RMS conversion automatically.

However, in both cases simply squaring the meter reading and then multiply ing or dividing by the resistance value of the load gives true power.

FYI:

Quite a few posting here misunderstand "true RMS" and think RMS calibrated is the same.

... Phil

Reply to
Phil Allison

** One that does is the " Keysight U1232A " 6000 count, hand held meter.

Despite the wrong information given in the published specs, AC response is *flat* from 20Hz to well over 20kHz. The upper limit being about 200kHz, at -1dBor so.

I was surprised and pleased to this find this out after buying one from Element 14 only last week to replace my 20+ year old Fluke 70-2. The Fluke still works fine, it just looks battered, with Gaffa holding the case together.

formatting link

.... Phil

Reply to
Phil Allison

John Doe wrote in news:ppu6l7$j96$1@dont- email.me:

Unlike you, a chronic, top posting, utterly and hopelessly self retarded Usenet dumbfuck.

Reply to
DecadentLinuxUserNumeroUno

So then what I have here is an average responding meter. Not peak. Makes sense. They could have just put that in the manual, or maybe I missed it but I did look at the AC specs because I was looking to see if it was TRMS and I think I would've caught it.

Reply to
jurb6006

RMS,

I am not being sarcastic, realy I want to know.

on the bench and hang a scope on the input to see for sure. But the way thi s generator works is pretty accurate.

on different waveform with the same peak value.

EWHERE, but how does it happen to read different ?

r I will have mustard and dill relish on my crow, along with a helping of f uckoff and fuckme.

g effect for a heater or filament bulb. If the peak voltage is the same for both waveforms - which can not be assumed to be so for a sig gen - there i s then much more area under the square wave than the sine, so more energy i s imparted to the load. Ie the rms voltage is greater for the square wave.

RMS stands for root mean square. The heating power of an electric current - the thermodynamic work it can do - is the square of the current times the resistance it is flowing through, or - for a stable resistance - the square of the voltage divided by that resistance.

If you can do calculus, you can integrate the area under a squared sine wav e over a half cycle, and compare that with a DC current or a square wave wh ich would do the same work.

--
Bill Sloman, Sydney
Reply to
bill.sloman

Well, I checked it against a TRMS meter and it is livable. It was OK on sin e, read high on square, and I don't remember on the half sawtooth but it wa s in the ballpark. The half saw goes like

_/|_/|_/|_

Looks relatively easy to calculate the RMS on that but why bother ?

Nice that it finally acted up again, years ago I worked on it, had all the "F" segments missing on the display.It was intermittent, I soldered it and it was alright for a timer but the problem recurred. Finally I pinned the s tandup board that feeds the display, the only other thing it could be now i s the resistor network and that is easy. Not bad for a second bench meter o r makes good trading fodder.

Now for this 8600a, looks like the big damn chip but we all know it might n ot be. Too many variables right now, but if I could get the chip cheap I th ink it would be worth a try. I'll be around when I get into that, but in SE R.

Reply to
jurb6006

snipped-for-privacy@gmail.com wrote in news:5fd89cc5-bf3e-47f2-81a8-b75e56101296 @googlegroups.com:

The whole RMS thing is not about reaching a value for a pure sine wave. That is extraordinarily easy. It is about giving you an accurate reading when you encounter a complex waveform, ya dopey ditzoflex.

Reply to
DecadentLinuxUserNumeroUno

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