Multimeters

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Thought I would test a greenlee clamp on multimeter that I bought at a rummage sale.
The greenlee read 123 volts.
The fluke I have is quite old and read 119 volts.
The harbor freight cheapie I have read read 121 volts.
Never tried this experiment before, all were digital and the max spread is as much as 4 volts.
I am surprised that the meters differ so much, apparently I should not have assumed all these years the readings I have been getting were pretty accurate because it was from a digital voltmeter.
Any experience in this area?

[MEXICOWANDERER]

For us electrical control freaks, that Voltage Reference, Model VREF-01 is like holding out a sack of "China White" in front of a junkie. Thanks for the link!

[Wayne_Dohnal]

For us cheapskates, there's a 0.01% DC reference available for $25.50 Voltage Reference, Model VREF-01. If that's too much, an LT1009CZ Voltage Reference Diode provides 0.2% accuracy for less than 2 bucks.

[MEXICOWANDERER]

" These calibration tools can cost tens of thousands of $$ each"

I got mine at at garage sale for eighty-seven-thousand-seven-hundred-dollars. a bid. It is the size of an old obsolete 23" television. It itself is calibrated by using N.I.S.T certification resistors one, ten, one hundred and 10K ohms. Interesting devices, the test probes, and connectors are gold clad. Products of Sandia National Laboratories. Using this stuff teaches the meaning of the word "Null" in a hurry 🙂

PS: A handheld nickel and dime "scope meter" has obsoleted the monster. I loaned this thing out back in 1997 and have never seen it nor the borrower since.

TIP: And it's a good one. A decent 4-3/4 digit DMM offers accuracy good enough even for technicians. These critters are getting less and less expensive.

[LScamper]

What ktmrfs says is exactly correct!

If two meters read the same it is a "Fluke"

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Interesting info, thanks for the input.
Joe

[wa8yxm]

If you download the owner's manuals for your meter there is a section called "Specifications" and in it is gives the accuracy of the meter. +/- N% where N is the accuracy.

4 volts is less than 4% and what's more it is +/- less than 2% of the same number, USUALLY this is well within the acceptable error for a low cost meter.

Now I have used some serious. Lab calibrated, meters (in college) and for those the error is a tiny fraction of a percent.. But you calibrate before every use.

What is more important than accuracy is repeatability.. Given the same source voltage, will the meter read the same time and time again.,

[So]

Four Meters - Fluke 88, Tektronix DMM150, Harbor Freight (freebie), Hampton Watt meter. I used the same Fluke test leads on all meters.

High voltage AC:









Low voltage DC:

Fluke 88



Tektronix DMM150



Harbor Freight

[Fishinghat]

WyoTraveler wrote:
I would believe the Fluke meter. John M. Fluke made some good meters.

X2

Fluke is a well established test equipment manufacturer, specializing in high tech equipment. Their oldest engineer, second in seniority to John Fluke was a friend of ours. He passed away over 20 years ago but I still remember him talking about the accuracy of their test equipment.

[EldIr]

I have a Fluke 77 that is nearly 30 years old. I've used it on and off numerous jobs over that span. Don't know how I'd get by without it. Best part is it was free. My brother, a now retired major tech company exec, gave a talk at Fluke in the mid 80's and they gave it to him as a token of their appreciation. He had no use for it so gave it to me.

[SCVJeff]

WyoTraveler wrote:
I would believe the Fluke meter. John M. Fluke made some good meters.

Well you know what they say:

"If it Works! It's a Fluke"

🙂

[ktmrfs]

How accurate the various meters are depends not only on the quality of the mfg, but the capabilities of the meter. Is it average responding rms calibrated, peak responding RMS calibrated? Is it true RMS reading?? etc. And how pure is the sine wave voltage source your measuring. Anymore, the line voltage coming into your house isn't as "clean" a 120V source of years ago, with all the stuff that draws power at the peak of the waveform.

So a true rms meter with good electronics will be able to get the real RMS value of the line voltage. the "average responding or peak responding RMS calibrated" won't, they ASSUME a PURE sine wave with NO harmonics.

Unless the FLUKE is VERY old, more than 20 or so, it is very likely a true rms meter with good electronics and a good RMS converter. Even if it is that old and not calibrated for a long time, it could be giving you the "most correct" AC voltage reading. Greenlee??? don't know. Harbor Freight, well there are cheap rms converter chips out there, but they really aren't that accurate.

Just because it's Digital doesn't mean anything about accuracy. There is digital junk out there and analog junk out there.

But, in reality, for RV applications, I'd say any of the three will give you the info you need.

Next measure your battery voltage. wouldn't be a bit suprised if you also get 3 different answers.

Personally all my test equipment is either Fluke or Tektronix. All NIST calibrated shortly before I retired. I know it's accurate and I know it's rugged and reliable. Equipment from either while it may have a 1year cal cycle, is in reality very very stable and often will be in spec for years or decades if you treat it right.

[hershey]

I have a Fluke left over from when I had a job. I use it as the benchmark for calibrating my other meters like a lighted volt meter that reads 3 volts low. And my Kill-a-watt that I leave plugged in for voltage display and it reads nearly exactly what the Fluke reads. Unfortunately it isn't lighted.

[PapPappy]

Hey, I'm all for proper calibration, and I'll use a Fluke before I use the Harbor Freight meter (though I have a HF meter that I keep in the RV)...but I'm not all that concerned about 2-3 volt difference....in the day to day stuff.

Yes, low voltage would be an issue for the A/C or some other components in the RV, but I feel that a quick check with the meter is good enough. Now, if the meter is showing a difference in excess of 10VAC at a campsite, I'll be worried.

As someone mentioned, it's really when you are working on tight clearances and low voltages that these numbers matter.
The the average RVer, any meter is better than no meter! And as with most things, try and get the best quality you can afford....it will be worth it in the end:)

[TucsonJim]

I've worked in electronics manufacturing for 30 years. Every multi meter we have is sent to our calibration lab once a year for checking and adjustment. I don't have the exact numbers, but recalling from my memory, I believe about 5-10% of them would be out of tolerance and have to be adjusted.

Normally, the variation is fine for 120VAC or 12VDC measurements, but can be a big issue of for very small voltage, resistance, current or capacitance when we were working on circuit cards and components with very stringent tolerances.

By the way, the units that we used to check calibration are calibrated to National Institute of Standards and Technology (NIST) standards. These calibration tools can cost tens of thousands of $$ each.

As mentioned above, the Fluke meters were some of the most reliable we had, and rarely went out of calibration tolerance.