Sorry to bother you again so soon but I could really use some help. It's been decided at work that, instead of calibrating all our hand-held multimeters, we will have one high end digital multimeter outsourced for calibration and validate our hand helds from that (I did suggest simply replacing the hand helds each year but that idea was nixed). So I need to write a work instruction on validating multimeters. Problem is I have very little idea how to do that. I tried searching the web but couldn't find anything. Could someone point me in the right direction?

What are you using them for? What functions on the multimeter do you want to 'validate'? Voltage? Resistance?

For voltage mainly running through our wiring harnesses. Many of our handhelds are used simply for go-no gauges so those at least can be listed as reference only. I doubt I'm the best person in the company to write this up but I'm the only one available; funny how that happens.

Although what you suggest is in theory possible, to do it right will cost more time and effort (therefore internal cost) than using an accredited calibration provider to cal the units.

http://inms-ienm.nrc-cnrc.gc.ca/clas/clas_e.html should get you to the SCC/CLAS website, you can find an accredited cal provider there.

Hope this helps.

Hershal

Sorry to bother you again so soon but I could really use some help. It's been decided at work that, instead of calibrating all our hand-held multimeters, we will have one high end digital multimeter outsourced for calibration and validate our hand helds from that (I did suggest simply replacing the hand helds each year but that idea was nixed). So I need to write a work instruction on validating multimeters. Problem is I have very little idea how to do that. I tried searching the web but couldn't find anything. Could someone point me in the right direction?

It is a long time since I did my electrical apprenticeship but I assume you test for zero before use. Set to 'Ohms' then touch both probes together then reset to Zero. I don't know how a high end multi will then calibrate all of the other handhelds. You could possibly buy/build a test box (known current and resistance) and then use this to calibrate before use. I don't like mucking around with calibration equipment especially electrical so I leave it up to the experts. Would your customers accept wiring harnesses that have been tested by internally calibrated multimeters? I doubt if an Aircraft manufacturer would let you get away with it and I doubt if the Auto companies would either. Just a thought - Ask your registrar and/or customer. Saving money in the short term does not necessarily save you money in the long term.

Thanks. My managers hav decided that they would prefer to do it in-house. I'd rather not but I know when not to push it. I found someone in R&D that showed me how to do it using a power source and connecting the two multimeters through the same banana cables (even got a free lesson in electrical theory).

You appear to have a good check method.....not a calibration method. AT BEST, and regardless of the accuracy of the higher end DMM, you achieve a 1:1 TAR (Test Accuracy Ratio). Once measurement uncertainty is calculated (a requirement under the internationally accepted definition for calibration) you will have a high uncertainty. Also, the specific traceability path must be documented. A controlled environment (23 C +/- 3 C) must be maintained for electronic calibration. The procedure needs to be a validated procedure, and the personnel trained.

If all these conditions are not met, and a calibration is a requirement, then I recommend that you outsource to a CLAS accredited lab near you.

http://inms-ienm.nrc-cnrc.gc.ca/clas/clas_e.html

Hope this helps.

Hershal

Thanks, Hershal. I really wish I could hire you for five minutes to talk to my managers but they seem pretty determined to do it this way. I'm the one documenting the procedure (always choose the person who knows the least, eh?) and I was techincally trained by an electronics engineer so I think it's CYA time for me.
Our ISO audit is this Thursday and Friday so sending out is no longer an option. My suggestion was to replace all the multimeters yearly with certified ones, but that was nixed.

I've already expressed my concern about this audit to the higher ups here, but they seem to think everything is going to be okay. Me, I'm staying out of the blast zone as much as possible.

Don't forget to dig the foxhole and cover it with armor.........