Help reading DMM Calibration report

[jeffjmr]

You have all touched on the reason for my initial inquiry.

Here’s the equipment used for the cal. It has been almost 10 months since the calibration.

It’s for my HP3478A by the way in case that helps.

Did you mean that your meter was calibrated 10 months ago or that the labs calibrator was calibrated 10 months ago?

This report is from my meter calibration done in May of 2021. As shown on my last pic the calibration equipment is due for calibration in July 2022.

Being totally ignorant (but learning) of calibration protocols and standards, I hesitated to reveal the cal lab, in case the report contained errors that would have resulted in the forum throwing shade on the lab.  I didn’t want to chance that.

I have the accuracy disease, and am feeling a TEA fever coming on as well. So I am spending way too much time trying to see if the meter still performs close to this report (without calibration equipment of course, limited to shorted inputs data, a DC voltage standard and some .005% resistors) and constantly comparing it to my K2015THD. Both exercises in futility but learning opportunities. I like to tinker, and if in this process of familiarizing myself with the mysteries of calibration I can find a component that isn’t performing as designed, I’ll solder in a replacement if I believe it could improve matters.

While most of the discussions among you experts is over my head, I’m still getting a clearer picture if how these things work, and for that I am most appreciative.

Jeff

[mendip_discovery]

You would only adjust the UUT if it is at a agreed percentage of the annual spec, or even the customers spec/requirements. The 24hr spec would be pointless spec to use for that.

And this is why a calibration certificate in general means so little to me.  This may be a widespread practice, but it does not mean that the meter meets the original manufacturer's specifications and confidence interval over the stated time and temperature spans.   Calibrating the instrument to the 24h/1C specs in a +/- 1C environment does give that assurance.  And there are calibration labs that do it that way by default.

For most of my customers that have stuff calibrated just want to know is it still within the specifications. The reason is that they produce a product and the UUT is used to test stuff they send out. If it is within specifications then they can carry on using it. If it is out of specification then they have to work out the potential risk that they have produced products that are potential risks. The fun bit is working out how long ago that was and which meter was used to do that test. In many cases they don't actually look at the trends of the equipment or undertake any interim checks on the equipment, many don't even know how to read the specs. I had one the other day that says that this process has to be temperature controlled to 1°C, using single a K-Type thermocouple, with hot water being pumped in at the side of a unit that is the size of a bus, that doesn't even come close to the Japanse manufactures who can't get the idea that the equipment in the machine even needs calibrating.

Lots of equipment doesn't come with elaborate specifications such as 24hr, 90 day etc. So hence most labs won't calibrate to those specifications and I suspect in many cases that specification is better than the uncertainty that the cal lab could produce.

I'm not seeing that and looking again I think you miscalculated the tolerances.  The HP manual lists the 30k range as .016% of reading plus 2 counts.  That works out to 18 counts at 10k, which is what they used.

You're completely right, I reversed the calculation of the uncertainty, converting counts to ppm of range, instead of ppm of value. So the tolerance for the 10k range does match the 1 year specification.

Alm, its not a TUR its a TAR, so its based on Spec, not uncertainty. Though I suspect it is actually quoting uncertainty just the lab is using a old label for TAR.

Being totally ignorant (but learning) of calibration protocols and standards, I hesitated to reveal the cal lab, in case the report contained errors that would have resulted in the forum throwing shade on the lab.  I didn’t want to chance that.

I agree, no need to name and shame. Often if you speak to the lab they are happy to explain any issues. Some just had odd ways of reporting tests.

While most of the discussions among you experts is over my head, I’m still getting a clearer picture if how these things work, and for that I am most appreciative.

Please don't accuse us of being experts, keyboard warriors maybe. If there are parts you don't understand *ask*.