True RMS multimeter?

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I bought an Excel XL 830L multimeter with the understanding that it was a RMS voltmeter.

I also have UEI ElectroMate DM 200.

When I checked the output of my APC unit with both meters, the readings were about the same.

Is there a way to tell if a meter is an RMS type?

Thanks,
         Andy  

Re: True RMS multimeter?
On Fri, 02 Feb 2018 16:02:52 -0800, Andy wrote:

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Simplest way is take a reading of the mains electricity in your house. If  
you're in europe it should come out at about 230-240VAC and the meter (if  
it's true RMS) will agree with that. I think in America and Japan the  
domestic mains voltages are very different but you will no doubt know  
what it should be in your own home country and a true RMS meter will  
agree with it.





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Re: True RMS multimeter?
Cursitor Doom wrote:

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** Any multimeter with AC ranges will give correct results on low frequency sine waves, like the mains power.  

  

.....  Phil



Re: True RMS multimeter?
On Friday, February 2, 2018 at 6:33:38 PM UTC-6, Cursitor Doom wrote:
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116 - 118V

Andy

Re: True RMS multimeter?
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That won't tell you jack shit. Non true RMS meters are calibrated for a sine wave. A volt will read 0.7071 anyway.  

Re: True RMS multimeter?
Andy wrote:

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 ** Can you see the term "true RMS" on the meter or handbook?  


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 ** Not a true RMS type.  


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 ** OK.

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** The maker will tell you.  



....  Phil

Re: True RMS multimeter?
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 ** Not a true RMS type. "

That should be all he needs then. Some sort of variable AC supply and some diodes or something to match the P-P value. Ba da bing, ba da boom. (well not boom hopefully, he only needs a volt, and one volt because it is convenient)

Re: True RMS multimeter?
They are all off base here. Actually I am surprised Phil didn't mention it.
  

Compare the readings with the same peak to peak value o a sine wave and a s
quare wave. If they read the same it is not true RMS. If it is true RMS on  


 has the resolution to discern 1 volt from 0.71 volt.  

You do have a scope right ? If not you'll have to figure out a way to clip  
a sine wave. You don't need any power behind it, a Zener or stack  of diode
s will do. A scope is the best way though. If you have to wing it come back
 and I will try to figure out the easiest way.

Re: True RMS multimeter?
snipped-for-privacy@gmail.com says...
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 you see youy are only partially correct.

 a 50% D square wave form = Vp *  1/sqrt(2)

 a RMS meter does not display 50% as you pointed out.  

 but, other references I've ran into will also state that the  
 RMS of a Square wave = VP, but that only applies to one half of the
complete cycle.

  Have fun..



Re: True RMS multimeter?
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 RMS of a Square wave = VP, but that only applies to one half of the
complete cycle. "

Well they're wrong because RMS has no polarity.  

Just like they talk about common base and collector amp stages. Truth is ALL amps are common emitter because the emitter is the common of the transistor.  

There are a couple of other things that are actually wrong, but accepted in practice.  

What's this VP anyway ? If it means voltage peak it is dead wrong and should be discarded as a reference.  

Re: True RMS multimeter?
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That's all under-specified. so not even wrong... are they measuring the AC
component or the total RMS voltage.

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yeah. but the fiction of the other topolgies makes design and anaylsis easier.

consider a darlington pair used common collector, which node do you want
to call ground?

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Re: True RMS multimeter?
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C component or the total RMS voltage. "

Trying to express it seems to be the problem. Both the positive and negativ
e sides of the waveform contribute, so it is not really half. But if you ha
ve a 1 volt P-P square wave, it is only going to read half a volt because a
 one volt symmetrical waveform would have the voltage going from half a vol
t negative to half a volt positive.Similarly if it is going from zero to on
e volt positive, it will read 50 % of that volt. That is where the one half
 comes in. Perhaps it would have been easier just to call it the peak value
 and forget peak to peak. But then the statement might be wrong on non-symm
etrical (+ to -) waveforms. They can just treat it all as positive.  

Words - dammit !

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to call ground? "

Not ground - COMMON. The emitter is common to both the input and the output
. You put current to the B - E junction and then the transistor starts cond
ucting from C - E. thereofre the E is always the common. How you ground it  
in the circuit will determine input and output impedances as well as voltag
e and/or current gain. But TO THE TRANSISTOR, the emitter is always common.
  

Another thing they teach wrong is that 180 out of phase is the same as inve
rting the waveform. Well they should not teach it that way because it is on
ly true for waveforms that are symmetrical on both axes. For example it is  
absolutely not true of a sawtooth wave. It IS true of a triangle wave but t
hat is different. The sawtooth is not symmetrical in both axes, only one, i
f it even is actually.  

Regardless, the point is that you can detect the difference in the reading  
to determine if the meter is true RMS. It seems like the sine and square co
mparison would be the easiest way to do it. the needed waveforms are the mo
st easily attainable.  

Anyway, I probably should've wrote the peak rather than half the peak to pe
ak. It would be a more accurate statement.

Re: True RMS multimeter?
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Why not the base, both "base" and "common" are antonyms or noble :^)

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No, it needs glide-reflection symmetry on one axis like the waveform you
get by low-passing a square-wave:
  
  _      ____         R                    __        __
   |    |    |   ---/\/\/---+------      .'  \     .'
   |____|    |__            |           /     `.__/    
                          ===== C    
   |----t----|              |                
                          --+--
                          /////
                 RC < t
  

In the frequency domian saying inversion is the same as 180deg phase
shift is completely accurate, in the time domain it sometimes works..


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Still ambiguous.

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Re: True RMS multimeter?
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Well put. So you DO understand it. But what about the beginner student ? I think it can cause more confusion in the future if they learn it that way.

Re: True RMS multimeter?
Actually it is only worth splitting hairs like this because this is sci.electronics.BASICS.  

Re: True RMS multimeter?
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It depends what they are learning, if they are learing transistors as a
device you can solder wires to to make useful circuits, the notion of  
common base etc is useful.

If they are wanting to write dissertions on the operation of solid
state electronics perhaps not so much.

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Re: True RMS multimeter?
snipped-for-privacy@gmail.com wrote:

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 ** It has magnitude, so always positive.  


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 ** Quite different really.  

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** The names describe circuits where one of the terminals of a transistor is COMMON to both input and output current loops. Any terminal can be.

  

.... Phil  

Re: True RMS multimeter?
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Yes, I fucked up the statement. Told you my sanity is gone.  

Re: True RMS multimeter?
On Sat, 3 Feb 2018 09:59:35 -0500, M Philbrook

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His inverter may be Quasi Sine wave. Not exactly 50% duty cycle.

Cheers

Re: True RMS multimeter?
On Fri, 2 Feb 2018 16:02:52 -0800 (PST), Andy

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True RMS is for wave shapes other than pretty sine waves.

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