Products > Test Equipment

Easy way to test the calibration of a DMM (Fluke 45)?

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Fungus:

--- Quote from: shabaz on April 03, 2024, 01:09:28 am ---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).

--- End quote ---

Humidity doesn't really matter if you're hand-soldering. It's more for ovens.

And if you're putting it in a socket, then...  :-//

Fungus:

--- Quote from: KungFuJosh on April 03, 2024, 01:14:48 am ---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.

--- End quote ---

Seems to me like somebody here could buy a bunch of them, calibrate them properly, and resell them.

CatalinaWOW:
Lots of trash talking here, backed with pedantic accuracy.

Yes, you do have to have traceability to assure accuracy, and history to assure accuracy over time.

I will be the first to admit that my array of meters all have long outdated calibrations and my similar array of sources are mostly worse, although I do have actual paperwork on my DMMcheck.  My meters are stable to several parts per million compared to the USA cal club reference, which is not formally calibrated, but TiN thoroughly evaluated it against multiple calibrated 3458s.  I can't truly claim that my equipment is calibrated or truly traceable.  But I am actually pretty confident that I know how good they are and feel that they do meet their specs (5.5 digit in several cases, 6.5 in one case).

 Maybe I got lucky on my cheap chinese reference, but it is stable relative to the other references, and the values on its sticker are in within a couple dozen ppm of the observed value. 

Labeling these things as junk in the context of a 3.5 digit meter is extreme.  Without additional measurement and calibration they are inadequate for much higher accuracy meters, and perhaps few of them are useful even with additional care.  So maybe in that context they are junk.

Perhaps the right way to ask the question is: If your budget is ~$20 dollars are they as good as anything else in the price range?  Are you better off with nothing than with one of them?  Are you better off using a pile of fresh alkaline batteries than with one of them?  Do you really believe that more than half are not within parts per 1000 (or even 10,000) of their stated output?

J-R:
The higher-quality references from Doug/Russ/Ian don't have any reports of fake calibration certificates.  They list out the specific calibrated equipment that was used and when they were last calibrated.  All three have been active here on the forums and many reviews have been published about their products.  (I use their names because we have them and also it's easier than pasting a huge line of URLs.)

Side note, Doug has some budget $35 single-voltage references that could be of interest to some: https://voltagestandard.com/01%25-voltage-references


It's true that not everyone needs the same level of performance from their test equipment, but these random unknown references really are bad no matter how you look at it.  The technical shortcomings have already been well discussed (and perhaps somewhat ignored), but a different point is that you are frequently contributing to people who would be totally fine scamming you wherever possible.  Instead, send your money to individuals who are not really doing it for the money but for the love of the hobby.  Win/win for everyone.


And again my main point about why these cheap references are "dangerous" is that they have specific voltages printed on them and are sold as "references" so buyers apply additional weight to them.  What ratio of buyers do we think have adjusted their DMM based on the "reference" compared to adjusting the "reference" based on their DMM?

tggzzz:

--- Quote from: shabaz on April 02, 2024, 11:35:10 pm ---"Or spend a lot more money, build a ref yourself, and still need to send it out for calibration (after hundreds of hours of runtime to confirm stability)."

Or, spend $5! and not send it for calibration, nor wait hundreds of hours (a ridiculous suggestion) because it will immediately tell you which of the two multimeters has the 20 mV discrepancy. Then, you know which multimeter might actually be functioning, and you can send it for a cal, at less than the cost of a calibrated reference.

--- End quote ---

When responding please use the "quote" button, and proceed from there. Doing that reduces ambiguity and increases comprehension.

Why spend $5? I'll sell you one for $0.50.

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