True RMS multimeter?

[Andy]

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

 

[Cursitor Doom]

On Fri, 02 Feb 2018 16:02:52 -0800, Andy wrote:

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?

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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[Phil Allison]

Andy wrote:

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

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

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

I also have UEI ElectroMate DM 200.

** Not a true RMS type.

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

** OK.

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

** The maker will tell you.



..... Phil

 

[Phil Allison]

Cursitor Doom wrote:

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

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


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.

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



...... Phil

 

[Andy]

On Friday, February 2, 2018 at 6:33:38 PM UTC-6, Cursitor Doom wrote:

On Fri, 02 Feb 2018 16:02:52 -0800, Andy wrote:

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?

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.





--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

116 - 118V

Andy

 

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 square wave. If they read the same it is not true RMS. If it is true RMS on a square wave it will read approximately ½ the P-P value but on a sine wave it will read lower, 0.70711 of ½ the P-P value. Almost any meter 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 diodes 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.

 

>"Simplest way is take a reading of the mains electricity in your house."

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

 

"> I also have UEI ElectroMate DM 200.

** 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)

 

[default]

On Fri, 2 Feb 2018 16:02:52 -0800 (PST), Andy
<andrewkennedy775@gmail.com> wrote:

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

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

 

[Phil Allison]

default wrote:

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

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

** Careful, true RMS works for sine waves too.



..... Phil

 

[M Philbrook]

In article <aade5a3d-8c9a-4a29-bd66-091233567694@googlegroups.com>,
jurb6006@gmail.com says...

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 square wave. If they read the same it is not true RMS. If it is true RMS on a square wave it will read approximately ? the P-P value but on a sine wave it will read lower, 0.70711 of ? the P-P value. Almost any meter 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 diodes 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.

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..

 

[default]

On Sat, 3 Feb 2018 04:48:34 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

default wrote:

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

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


** Careful, true RMS works for sine waves too.



.... Phil

Yup, my omission.

 

>" 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. "

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.

 

[Jasen Betts]

On 2018-02-03, jurb6006@gmail.com <jurb6006@gmail.com> wrote:

" 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. "

Well they're wrong because RMS has no polarity.

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

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.

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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This email has not been checked by half-arsed antivirus software

 

[Phil Allison]

jurb...@gmail.com wrote:

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

" 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. "

Well they're wrong because RMS has no polarity.

** It has magnitude, so always positive.


> Just like they talk about common base and collector amp stages.

** Quite different really.

Truth is ALL amps are common emitter because the emitter is the
common of the transistor.

** 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

 

>"That's all under-specified. so not even wrong... are they measuring the AC component or the total RMS voltage. "

Trying to express it seems to be the problem. Both the positive and negative sides of the waveform contribute, so it is not really half. But if you have 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 volt negative to half a volt positive.Similarly if it is going from zero to one 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-symmetrical (+ to -) waveforms. They can just treat it all as positive.

Words - dammit !

>"consider a darlington pair used common collector, which node do you want 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 conducting 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 voltage 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 inverting the waveform. Well they should not teach it that way because it is only 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 that is different. The sawtooth is not symmetrical in both axes, only one, if 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 comparison would be the easiest way to do it. the needed waveforms are the most easily attainable.

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

 

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

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.

 

Actually it is only worth splitting hairs like this because this is sci.electronics.BASICS.

 

>" ** It has magnitude, so always positive. "

Yes, I fucked up the statement. Told you my sanity is gone.

 

[Martin Riddle]

On Sat, 3 Feb 2018 09:59:35 -0500, M Philbrook
<jamie_ka1lpa@charter.net> wrote:

In article <aade5a3d-8c9a-4a29-bd66-091233567694@googlegroups.com>,
jurb6006@gmail.com says...

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 square wave. If they read the same it is not true RMS. If it is true RMS on a square wave it will read approximately ? the P-P value but on a sine wave it will read lower, 0.70711 of ? the P-P value. Almost any meter 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 diodes 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.

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..

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

Cheers