So, how do I handle calibration of a small pile of multimeters? - Page 1
Forum section: electronics / testgear

author: SingedFingers
author_rank: Frequent Contributor
timestamp: January 14, 2017, 01:04:30 pm
content: It turns out I have a problem to deal with. Apart from finding another meter, a nice Micronta one... Calibration. Stuck everything on my PSU (PL330) and did loaded the meter on my Heath supply via the outputs.* TTi PL330: 10.00v* Heath 2718: ~9.9v (analogue)* UT81E: 9.976v* D03046: 10.01v* PM2524: 9.982v* Micronta 22-214: ~9.8v (analogue)* Fluke 8010A: 9.98v* An unknown 8020A turning up next week.What can I do about this. I'm thinking a cheap voltage reference. Are there any good ones on the market?Note: don't want to be a voltnut - just want to calibrate all these against a standard.

author: EEVblog
author_rank: Unknown
timestamp: January 14, 2017, 01:08:35 pm
content: Just compare them on all the ranges.You have a 0.34% spread from highest to lowest on the digitals, they are already pretty good and likely within spec. Do you want better on such old meters?Calibrationadjustmentis another thing entirely.

author: tautech
author_rank: Super Contributor
timestamp: January 14, 2017, 01:17:34 pm
content: http://www.voltagestandard.com/DMMCheck.html

author: Fungus
author_rank: Super Contributor
timestamp: January 14, 2017, 01:38:39 pm
content: They all look fine apart from the analogues.The lowest is 9.97, the highest is 10.01. An error of 0.3% is well within spec for most meters. .You could try taking the backs off and looking for adjustment pots but the calibratable ones will probably have four or five of them and you won't know which one to turn for "DC 10V". It will be trial and error. You might mess up other ranges.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: January 14, 2017, 01:44:13 pm
content: Ok that sounds better than I was expecting if I exclude the analogue ones. Thanks for everyone's input.The micronta I have service info for and it has per range calibration so i'll adjust that. The Heath one is a dick; no calibration adjustments and the dial is sticky. I'm probably going to get rid of that one though as I only use the TTi supply.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: January 14, 2017, 01:47:48 pm
content: Quote from: tautech on January 14, 2017, 01:17:34 pmI've semi persuaded my wife to buy me one for my birthday

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: January 14, 2017, 02:38:38 pm
content: On the analogue ones it would be pretty simple to measure the individual resistors to see if they are within specs to calibrate it. It works with the basic non trimable type multimeter.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: January 14, 2017, 02:59:51 pm
content: Well Micronta one is done. Took a while as I have no service info. I did actually check the divider resistors and they were all about right based on some simple calculations. Metal film 1% variety. I also got a bit of a surprise inside it. It has MOVs in it and sand filled fuses. Not bad for a 1980s shitty meter. The 10A shunt is however to use a London phrase "dodgy as f**k".It does however have a very annoying problem: you can't get it to do a full scale deflection post calibration unless it is lying down. You lose about 5% of total scale which is a little to high to live with. I think the movement in it isn't very well balanced.eBay time!