Multimeter voltage calibration

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JHZR2

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I have a few of those HF multimeters, Ive gotten them via free coupons or one as a gift. I also have a nice Fluke 179 which I use for detail work where fractions of a volt and tiny differences in resistance can make differences. I had noticed that the HF meters all read all over the place. One was very noisy as well. So I decided to calibrate them just to the values that my Fluke reads, which should be pretty accurate. I first attached the fluke and a set of leads to the battery I was using as a test basis. This is the oldest one I have. This one someone bought to give as a gift. I wouldn't have the guts to calibrate the fluke, and I think its done an entirely different way... But these just have a simple potentiometer to adjust, so its really easy... All better: This one was way off, and really noisy. I got it better but its incredible. The lack of calibration on these things, and how they drift could be dangerous, or cause stuff to be condemned that doesn't need to be. The Innova cigarette lighter voltmeter I have is spot on with the fluke. I guess this is why HF can give them away free. Worth a look if you can take your cheapo someplace to compare and make it correct. Hopefully some are better than others...
 
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When I repaired medical equipment long time ago, Davis Calibration (now Tektronix) would calibrate all test equipment yearly. I got a Fluke 123 from work that I have in my 'tool box' Obviously the lower end test equipment is off a bit compared to the high end stuff.
 
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So say you were 13.58 VDC on the Fluke. Will the tweaked meter read 13.58 VDC ? I have 2 ancient flukes and a Wave Tech that is a 50$ meter 15 yrs ago . It reads within a .01 of the flukes I gave my son a real cheap AC/DC multi meter. I'll bet it is tweakable. We used to adjust power supplies and battery float for the phone company by adjusting pots.A milli volt or 10 is no big deal on an automotive system. But the idea of zeroing in a cheap meter appeals to me. Thank you for the tip grin2
 
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I have 2 free newer Cen-Tech DMM's, I don't have any reference meter to calibrate. 6.5% error with your free DMM is very high, the yellow error is less than 2% is probably okay for most use like checking alkaline battery.
 

JHZR2

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Originally Posted By: andyd
A milli volt or 10 is no big deal on an automotive system. But the idea of zeroing in a cheap meter appeals to me. Thank you for the tip grin2
Sometimes I run experiments on billion dollar equipment where a millivolt or ten does make a difference. Of course then we calibrate stuff routinely... Something like battery state of charge can be different at the second decimal place. Other stuff may not make a difference...
 
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Just to humor me, would you grab another Fluke and see if both Fluke gives you the same readings? You know where this is going, right?
 

JHZR2

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Originally Posted By: Vikas
Just to humor me, would you grab another Fluke and see if both Fluke gives you the same readings? You know where this is going, right?
I actually have a DC ammeter clamp that has a volt meter circuit built in. It's due for recall, but when I get the replacement, I'll check it. Sure, the 179 could be off too. But which came with traceable calibration, and which is free by the truckload? Yes, the fanciest gadget can be inaccurate, and if it is, then I calibrated others to an inaccurate place. The saving grace is that we know a 100% SOC lead acid battery is around 12.7V open circuit at room temp. Mine had a surface charge which was depleting, but it wasn't way off from expected value, and settled to where I expected it to be.
 
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My free red centech is about the same as my $20 E tek from Walmart but the differences between your two meters scares me! A good Fluke meter is definitely on my WTB list. I wonder how fast my meters are off?
 
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I had a red cen-tech which when new, matched my friends Fluke within .01 at 12.8 and .02 at 14.7 and foolishly I trusted it to stay that way. I wound up setting some solar acceptance and float set points by it, and long story short, I overcharged an expensive set of batteries. When i checked it again against the same Fluke, it was reading .35 volts lower than actual. Changing the 9v battery did not help. I've more recently acquired a Sears DC clamp on Ammeter, which also reads inline with the fluke, and .35 volts higher than the Centech. I still use the Centech, or lend it out, but I do not trust it. I will recalibrate it and see how quickly it drifts. thanks for the heads up on the Pot.
 

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Interesting on drift. Wonder how these will drift/how stable they are. I see tons of reports of the fluke meters still being in spec 10-20 years after manufacture. Hopefully the modern ones are as good...
 

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So per above it seems like they may be prone to drift. I don't know how but I suppose it's reasonable. How long ago was that pic taken? Would be interesting to see the same today.
 

JHZR2

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Originally Posted By: Vikas
Those two pictures were taken on 2011-01-26.
So the drift question would be helped by taking a new shot of the same kind of thing before tweaking the pot on the centech to see if it has drifted...
 
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