# AC meter

Discussion in 'General Electronics Chat' started by DexterMccoy, Mar 27, 2014.

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1. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
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Most DVM meters in AC mode can't indicate what polarity or phase the AC waveform is , is the AC waveform in phase or out of phase

Older DVM meters in AC mode could tell if the AC waveform was in phase or out of phase

The DVM meter would have a (-) polarity for AC waveforms that were out of phase

The DVM meter would have a Reference input port

How would you make or how can you modify a DVM meter to have an Reference input port?

Why Don't new DVM meters have a reference port?

2. ### crutschow Expert

Mar 14, 2008
13,498
3,374
Meters don't have a reference port because few AC measurements are made where the phase of the AC signal is important. And, if it is, then an oscilloscope is typically used for that purpose.

If you are only concerned if two signals are in-phase or 180° out-of-phase then just measure the voltage between the two signals. In-phase will give a voltage equal to the difference in voltage between the two. Out-of-phase will give a voltage equal to the sum of the two voltages.

3. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
I got the same voltage for the in phase and out of phase, so how can you tell which voltage is the "difference"? and which voltage is the SUM?

4. ### crutschow Expert

Mar 14, 2008
13,498
3,374
Did you measure the voltage by connecting one voltmeter probe to one signal and connecting the other probe to the other signal? That's why I meant by "measure the voltage between the two signals". I though that was clear but obviously that's not the case.

5. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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You're talking about measuring Two completely different waveforms or two different Outputs

I'm talking about measuring ONE AC waveform, how can you tell with a DVM meter if the AC waveform is in phase or out of phase by 180 degrees?

The DVM meter needs a REFERENCE INPUT ports , how can I make this?

6. ### #12 Expert

Nov 30, 2010
16,690
7,330
Connect one lead of the voltmeter to the reference wave.

There is no such thing as, "out of phase" compared to nothing. Phase is always relative to some other wave.

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