Correct house voltage on a voltmeter

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Old 12-19-19, 08:29 AM
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Correct house voltage on a voltmeter

I am measuring 95vac at an outlet in my house on an OLD sears / craftsman VOM / multimeter. and 188 across the 2 hots

With a cheap harbor freight VOM, I am getting 125 and 250

There's different ways to calculate AC power and that 95/188 are likely 'normal', right?

VDC and ohms match between meters.

This is the old unit - didn't see a copyright date in the manual. But it's 20+ years old I think.

Any thoughts on the difference of AC voltage? the things I do is more to see - is there power there or not. actual voltage isn't relevant. So I'll keep it around. just curious if anyone knows of a way to recalibrate it or it likely uses a different formula to measure ac, or some other trivia about this?

THANSK!
 
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Old 12-19-19, 08:34 AM
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Show us a photo of the Craftsman meter. It should have a means to calibrate the unit.
 
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Old 12-19-19, 08:35 AM
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The old meter is having a problem reading AC voltage. It probably needs to be retired to the trash.

I'll add if it is an analog meter with a needle it may need the adjustment screw at the base of the needle turned to get the needle back in the correct reading.
 
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Old 12-19-19, 09:13 AM
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Yes there are different ways to measure AC.
Instead of RMS the old meter may be reading average or mean voltage.

I would scrap it.
The norm these days is RMS so if you come onto a help site and say I have a problem and give a mean or average voltage then the response will be you have a power problem and you could spend days chasing that when in fact your power is OK.
 
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Old 12-19-19, 09:50 AM
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Quick lesson in some basics:

Power is not measured with only a voltmeter. Power is the RMS V times RMS current (I) at an instant in time on or towards, a load.

The average Voltage on a wall outlet is zero. There are just as many points of Positive Voltage as Negative Voltage. The algebraic sum will be zero. You will though see "average responding" ac voltmeters. This really just means that the scale is calibrated to show "rms" and not "peak" or "peak to peak" values. It also usually means the internal circuit will not measure true RMS, and, if measuring something not sinusoidal, will have errors.

An RMS Voltmeter is not usually necessary in the electrical/power industry, with a few, critical exceptions related to high harmonic content. It is actually far more useful to use rms responding Ammeters, since many loads are not resistive, and the resulting current waveform is very much not a sinewave. Not usually true for the Voltage.
 
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Old 12-19-19, 11:19 AM
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Thanks guys!

Here's the pics
 
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Old 12-19-19, 11:32 AM
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If the 95 and 188 vac readings were measured on the same VAC range selection of the VOM, it is possible the meter's range resistor for that VAC position has changed value. This would not have any affect on the remaining VOM functions, including VAC on other range selections unless the faulty resistor is used by other VAC ranges (for proper meter movement) as well. No need to trash the VOM in my opinion.
 
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Old 12-19-19, 11:43 AM
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beezlebob - it's autoranging... you can press a range button to change the resolutiuon. But pressing it the 95 stays the same / may add a zero... or then O/L for measuring too high a voltage for that range.

Not sure if it's changing resistors like other types of VOM with several manual positions on a dial.
 
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Old 12-19-19, 12:10 PM
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Sorry. I had not seen post #6 when I created post #7. I assumed your old meter was an analog type. The only thing I know about a digital VOM is the input must be digitized somewhere between input and display.
 
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Old 12-19-19, 12:14 PM
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I cannot find any info on it but it should be reading RMS.
So I still say trash it.
 
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Old 12-19-19, 02:25 PM
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Does it have fresh batteries?
Geo
 
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Old 12-19-19, 05:34 PM
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I agree with Geo. Weak batteries will give odd readings on a meter.

Google "craftsman 82139" and lots of info will come up.
This also might be helpful: https://www.manualslib.com/products/...9-2844852.html

BTW - That meter doesn't look that old to me.
 
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Old 12-19-19, 05:40 PM
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I have the same model of Multi-meter that I got way back when sears was still mostly alive and well. I believe I paid around $25-$30 Anyway I had the same problem when the batteries were low but if you change the batteries and still have the same problems I say trash it. I also attached a PDF I have of the manual.
 
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Last edited by CircuitBreaker; 12-19-19 at 05:42 PM. Reason: Information is now null and void as post #12 was not there while I was making my post :)
 

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