Products > Test Equipment
Easy way to test the calibration of a DMM (Fluke 45)?
shapirus:
--- Quote from: KungFuJosh on April 03, 2024, 12:34:38 am ---As was mentioned, most of those $5 refs come with bullshit cal sheets that are copied over and over again and are completely useless.
--- End quote ---
"Most" is either ambiguous, or has to be proved. Since this thread has a slight hint of metrology, I would reword it like so: there is a significant number of bogus cal sheet reports on certain types of those ref boards. At the same time, many appear to be legit, but none seem like they can be traced to an instrument with a valid calibration certificate.
Fungus:
--- Quote from: shapirus on April 03, 2024, 12:42:35 am ---
--- Quote from: KungFuJosh on April 03, 2024, 12:34:38 am ---As was mentioned, most of those $5 refs come with bullshit cal sheets that are copied over and over again and are completely useless.
--- End quote ---
"Most" is either ambiguous, or has to be proved. Since this thread has a slight hint of metrology, I would reword it like so: there is a significant number of bogus cal sheet reports on certain types of those ref boards. At the same time, many appear to be legit, but none seem like they can be traced to an instrument with a valid calibration certificate.
--- End quote ---
There's many threads discussing these references, eg.
https://www.eevblog.com/forum/metrology/are-cheap-ad584-units-worth-it/
https://www.eevblog.com/forum/testgear/cheap-chinese-ad584-voltage-reference-legit-cal-data-let_s-find-out!/
https://www.eevblog.com/forum/metrology/cheap-ebay-ad584-voltage-references-my-experiences/
shabaz:
"if the POS $5 ref you buy agrees with one of your meters, it doesn't tell you anything without valid calibration"
I'm almost speechless that you can't engineer a way to determine a 20 mV discrepancy without "valid calibration".
It's really not rocket science.
shabaz:
Really ugly prototype, but it seems to indicate that even an unrecommended layout of the REF50xx chip will perform for the use-case being discussed.
I didn't have many through-hole parts, so I've used SMD capacitors with wires soldered on.
The parts used are:
REF5045AID (stored in an unsealed packet with humidity indicator indicating humidity is present, and the purchase date on the sticker is Dec 2014, i.e. 9 years old).
Input capacitor: 22uF, TPSB226K010R0700
Output capacitor: 4.7uF, TPSA475K010R1400
Noise reduction capacitor: 1uF, TPSA105K035R3000
Input supply: 9V PP3 battery
Just a quick measurement with a Fluke 87V was 4.503V, so it certainly appears to be a good result, but I'll measure with a DMM6500 tomorrow (and will also try some more samples of that part, plus some REF5020AID.
KungFuJosh:
--- Quote from: shapirus on April 03, 2024, 12:42:35 am ---
--- Quote from: KungFuJosh on April 03, 2024, 12:34:38 am ---As was mentioned, most of those $5 refs come with bullshit cal sheets that are copied over and over again and are completely useless.
--- End quote ---
"Most" is either ambiguous, or has to be proved. Since this thread has a slight hint of metrology, I would reword it like so: there is a significant number of bogus cal sheet reports on certain types of those ref boards. At the same time, many appear to be legit, but none seem like they can be traced to an instrument with a valid calibration certificate.
--- End quote ---
Most by definition means more than 51%. I was being generous since from the numerous threads and examples I've seen, only one had a seemingly valid cal sheet. I also have purchased a bunch of these, and know from experience most of them are not worth the $2 shipping fee. I also mentioned the $20 range, because this ~$22 example was the best of all the shitty refs I bought from any only retailer for less than $100: https://www.aliexpress.us/item/3256804431053626.html
ETA: Another reason I don't like non-calibrated sources is because I find it pretty easy to have multiple DMMs disagree with a ref that one DMM might agree with. Hence the need for calibration.
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