Author Topic: Reference PCB for Calibrating DMM's  (Read 3770 times)

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Offline dophuc

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Re: Reference PCB for Calibrating DMM's
« Reply #25 on: November 26, 2022, 09:15:38 am »
I usually use LB02A as a device to calibrate DMM or power supply, the accuracy of LB02A is about 0.025% and many functions like: V (1-11V), mA (0-24mA) Ohm (0-2200 Ohm) , ... especially simulates various types of thermoelectric signals Type T, J, K, ...PT100, PT1000...
Not extremely accurate but versatile and under $100 (I bought it on Aliexpress for $74 on sale  ;D)
« Last Edit: November 26, 2022, 09:25:26 am by dophuc »
 

Offline robert.rozee

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Re: Reference PCB for Calibrating DMM's
« Reply #26 on: November 26, 2022, 01:45:41 pm »
i believe the original poster, JenniferG, was just after doing a sanity check on her two meters (one 5½ digits benchtop, the other 4½ digits handheld). i'm picking that the Instek GDM-8251A (benchtop) is far more likely to be reading true.

for this sort of check one doesn't need anything too fancy, and a 0.01% resistor of known value and a 5v MAX6350 or similar would be fine. no need to go overboard buying a "DMMCheck Plus" or similar. indeed, for the average electronics hobbyist, a 2% accuracy 3½ digit multimeter is mostly fine!


cheers,
rob   :-)
 

Offline JenniferGTopic starter

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Re: Reference PCB for Calibrating DMM's
« Reply #27 on: November 26, 2022, 06:52:05 pm »
i believe the original poster, JenniferG, was just after doing a sanity check on her two meters (one 5½ digits benchtop, the other 4½ digits handheld). i'm picking that the Instek GDM-8251A (benchtop) is far more likely to be reading true.

for this sort of check one doesn't need anything too fancy, and a 0.01% resistor of known value and a 5v MAX6350 or similar would be fine. no need to go overboard buying a "DMMCheck Plus" or similar. indeed, for the average electronics hobbyist, a 2% accuracy 3½ digit multimeter is mostly fine!


cheers,
rob   :-)

Yeah the UT61E seems a bit off compared to the GW.  But also I've never tested my Gwinstek to see how close it is to be accurate.  I bought it used in 2017 off ebay and it's been sitting here; just finally now I've really gotten interested in electronics.  It came from the big sale of ITT equipment when they shut down.  It doesn't have a calibration sticker on it.
Test Equip: GDM-8251a, UT61E, Probemaster, Tektronix 2225
Power Supplies: GPD-3303S (w/o overshoot problem)
Soldering Station:  Hakko 926
 

Online bdunham7

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Re: Reference PCB for Calibrating DMM's
« Reply #28 on: November 26, 2022, 07:43:15 pm »
Yeah the UT61E seems a bit off compared to the GW.  But also I've never tested my Gwinstek to see how close it is to be accurate.

How much off? By the specs, at the UT61E has an uncertainty of +/- 51mV, while the GDM8251A is +/- 1.7mV, or 30X better.  In real life, I'd expect the UT61E to be better than its specs by quite a bit, the GDM8251A not so much, so maybe 5-10X better.  The expectation would be that any small discrepancy (<50mV @ 10V) would be likely mostly due to the error of the UT61E, but a large discrepancy is equally likely to be either one since that would indicate a gross failure on the part of one or the other.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline mawyatt

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Re: Reference PCB for Calibrating DMM's
« Reply #29 on: November 26, 2022, 11:22:24 pm »
Here's something the OP & others may find interesting.

https://www.eevblog.com/forum/testgear/ac-rms-dmm-tests/msg3940957/#msg3940957

Been running continuously for a couple years and still producing good results.

Edit: Update just checked last night and the device had failed, just completed update & repair on the mentioned thread.

Best,
« Last Edit: November 27, 2022, 11:38:23 pm by mawyatt »
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 

Offline Kleinstein

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Re: Reference PCB for Calibrating DMM's
« Reply #30 on: November 27, 2022, 11:48:36 am »
For the UT61E I would expect it to be quite a bit better than the specs when new, but there is a chance that it will drift over time. The tolerace specs are not so much for the initial value but likely to a large part to allow for some dirft for the next 1-5 year (so the meter has a chance to pass calibration even after 4 years).  Getting the calibration right from the start is not that difficult and expensive, but keeping the drift low is tricky and costs money.
There usually are no seprate 30 days or 3 month specs for these lower rated meters, but expect quite some difference.

The older age GDM8251 may already had some dirft from aging. So I would not count on having it really much better than the specs.
 


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