PM2525 Calibration - Page 1
Forum section: electronics / testgear

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 04, 2018, 11:43:13 am
content: Following some discussion on here I was offered a PM2525 by a member (thanks _Wim_) who had two a brown one thats accurate and a white one which is a little inaccurate. I decided to buy both because the price was right and the white one would be spares for the first or a backup etc... Anyway they duly arrived and are working so everything is as expected. The white one is showing "nc" and it's accuracy is maybe 0.5% out from the brown one which is close to my UNI-T60E so I'm again happy with that.So on the the question of calibration as I would like to sort the nc on the white one. I've got the manual and the calibration part has a page which appears to be two pages copied into one with possibly one missing. The same copy is all over the internet with the same page missing.It says I need the following:a 2uF capacitor (0.5%)a 20nF capacitor (0.5%)a 1Mohm resistor (0.1%)a Philips PM9264/01 four wire ohm cablea Philips PM5390 Frequency generatora Philips 5100B multifunction calibrator (or equivalent)Right so the components are simple enough and thanks to a thread on EEVblog I've got the stuff to build the PM9264/01 lead. I own an arbitrary wave generator so can use that to provided a frequency but do not have their generator but the calibrator is something I've not got and it wouldn't be worth getting.Am I stuck at this point?Oh and I've just ordered a new CR2 battery and holder to replace the 0.3V (doh!) lithium battery that was in the unit!My workshop is currently at 3.2 degrees C so I might have to bring it all inside the house too!Lastly anybody know if the LCD screens on these things are unique to them or a standard part as both screens are slightly damaged.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: February 04, 2018, 12:34:48 pm
content: I don't think that you need that exact gear to do it. The way that I calibrated most of my meters (4.5 digits and below) is simply by comparing to a calibrated 6.5 digit meter with far better specs.For example, at some point it might tell you to apply a 10 V voltage. What I would do here is just take a regular DC power supply, put the good meter in parallel to the one being calibrated, and then just tweak the voltage of that power supply (using a resistor devider or such to provide very fine tuning) to 10.00000 on the good meter.Sure, it might not be the optimal way, but I think it is fine for home usage.(similar things can be done for other ranges. I am not familiar with calibration of the 2525, so it could be harder here. Doing this is easiest with old meters that use trimmers)

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 04, 2018, 12:56:05 pm
content: Quote from: TheUnnamedNewbie on February 04, 2018, 12:34:48 pmThanks. I'm not sure from the manual how it does it. I have the second PM2525 so would be happy to effectively calibrate them to the brown one so long as I can do that......

author: alm
author_rank: Super Contributor
timestamp: February 04, 2018, 02:10:34 pm
content: The multi-function calibrator is able to provide DC voltages up to 1000 V, AC voltages up to 1000 V / 50 kHz (not both at the same time), DC and AC currents up to 2A and resistance from 1 Ohm up to 10 MOhm, with decent accuracy, all in one neat (but not so small) package. The extra components (like the resistor) are to supplement it with values it can't generate or not with sufficient accuracy. To replace it, you will need some other way of generating these signals. Check the PM2525 documentation to see which of these values are actually necessary.To calibrate the 1000 V DC range, you will likely need a DC voltage source close to 1000 V, which is not available from common bench supplies. Electrophoresis supplies have been proposed as a cheap alternative. A high voltage AC source (e.g. 1 kV 1 kHz) can also be tricky. Depending on the instrument, you may be able to do only a partial adjustment for the ranges / functions you care about.You can use a lower specced source (e.g. bench supply) plus an accurate DMM (ideally significantly more accurate than the DUT), provided the source is sufficiently stable for ten minutes or so. I have tried to use a cheap bench supply to compare 6.5 digit DMMs, and it turned out to be an exercise in frustration, since the value would wander all over the place. The best I got was hooking up two meters in parallel and recording averages over at least a couple of minutes. And this was only verification, not adjustment. Trying to adjust a high-resolution DMM to a 1/4 W metal film resistor is also interesting (heating from the test current will change the value).

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 04, 2018, 03:01:22 pm
content: Thanks. The high voltages are irrelevant to me so as long as it’s ok up to 50v I’m happy. I have the other one and I plan on buying a decent DMM later