DMM Calibration?

[Les_Garten]

Hi,

I think I know the answer to this but I'll throw it out anyhow.

I have some DMMs and would like to know about what you guys do with respect to calibrations.

So I'll use 2 of my DMMs as an example. Fluke 87 and NEW VC99.

I put them both in an electrical outlet at the same time and they both show the same V. The Fluke I bought around '96, the VC99 is about a month old.

My plan is to measure some caps, resistors, etc and see how much they agree. So far the voltages measure the same. I'm not sure what it tells me if they disagree, but I thought I would just play around with a NEW meter and my Ol' Fluke.

I may just send off the Fluke and get it calibrated, but I don't really want to just chuck cash away either.

What do you guys do? Has anybody done a recalibration?

[cetoole]

What are you doing that actually requires calibration? I would think for most DIY work, all that you really would need is repeatable results, as opposed to absolute values being exactly on.

[Les_Garten]

What are you doing that actually requires calibration? I would think for most DIY work, all that you really would need is repeatable results, as opposed to absolute values being exactly on.

Well that's what I'm trying to figure out. Lets say I built a B-22. During any troubleshooting there are test points, that's the extent of what I would do. I have an "old" DMM and was just wondering if anybody ever sent them back to recal, and if there is really a need for it.

My plan is to proof the two DMMs against each other and if they are about the same, I'll determine no need.

[cetoole]

I would be surprised and worried if your meters were so far off as to be unsuitable for that sort of work without calibration. Probably to the point where I wouldnt be looking at calibration, because I would be worried that something has blown in the meter itself.

[luvdunhill]

I would think for most DIY work, all that you really would need is repeatable results, as opposed to absolute values being exactly on.

DC offset? That's the one thing people shouldn't be using those crappy Harbor Freight meters for.

[cetoole]

But he doesnt have a Harbor Freight meter. You are right, you dont want DC offset to be off much, but on any half decent meter, I kind of doubt that would be too much of an issue.

[Les_Garten]

I guess my distilled down question is how much does a good meter drift over time in anybody's experience. Mine has been babied and not used much to be honest. I guess it has spent some time out in the garage though.

Cost of Recal is $48 + Shipping. Not much, but still about $50 I could use for something more tangible.

[n_maher]

Buy some tight tolerance resistors, measure the group, judge for yourself. Better yet, buy some sets in wildly separated values, test them all.

[Les_Garten]

Buy some tight tolerance resistors, measure the group, judge for yourself. Better yet, buy some sets in wildly separated values, test them all.

That's kinda where I was going. I also have a third NEW meter somewhere that I can use for trending purposes. It's real cheap, slightly better than a harbor freight... maybe...

[luvdunhill]

Cost of Recal is $48 + Shipping. Not much, but still about $50 I could use for something more tangible.

that's not bad. Is that through Fluke? I want to ask them about the insane battery drain on my meter, perhaps they'd look it over while it is in?

[Les_Garten]

that's not bad. Is that through Fluke? I want to ask them about the insane battery drain on my meter, perhaps they'd look it over while it is in?

Hey,

That was a company in S.FL I found looking for Florida Calibration services. They do it onsite, which is apparently a big business, that is, the calibration business. These guys who do this are certified Metrologists or something such. If they already have it, you would want to check on a quote maybe. I think they charged about $100 extra for my meter originally if I bought it Calibrated. Which I did not originally.

Ciao

[Dusty Chalk]

I should do mine too -- the main reason I have mine is to bias tube amps.

Buy some tight tolerance resistors, measure the group, judge for yourself. Better yet, buy some sets in wildly separated values, test them all.

Is that the same thing as voltage? I mean, that's kind of a loaded question, because obviously it's not, but is checking its ability to measure resistance accurately the same as checking its ability to measure voltage accurately? I don't think they have high tolerance batteries.

[n_maher]

I should do mine too -- the main reason I have mine is to bias tube amps.Is that the same thing as voltage? I mean, that's kind of a loaded question, because obviously it's not, but is checking its ability to measure resistance accurately the same as checking its ability to measure voltage accurately? I don't think they have high tolerance batteries.

No, it's not the same thing, but you could do something similar by taking a known voltage and building a series of dividers to check a range of voltages too. It was just a suggestion of one easy thing to check that might hint at how the meter is doing.

Me, I wouldn't worry about it. I'm with the camp that says as long as the meter provides repeatable/consistent results rather than pin-point accuracy it's doing what I need it to do.

[Fitz]

Even when years out of calibration any half-decent meter will still be way more than close enough for this kind of stuff. I'd sooner get a meter with higher precision than calibrating a regular DMM... precision > accuracy for audio DIY, IMO.

Edited January 6, 2010 by Fitz

[grenert]

If you want to check you DMM's DC voltage accuracy, Joe Geller sells some very reasonably priced, calibrated 10V standards.

Geller Labs Products

He's also the guy who made the JCan resistor noise measurement device. More DIY insanity fun!