DMMCheck Plus Calibration Certificates - Page 1
Forum section: electronics / general

author: rkeller
author_rank: Contributor
timestamp: March 06, 2025, 02:40:22 pm
content: Good Day All: To answer some questions we posted a video on how to find the test equipment calibration certificates used when we measure each DMMCheck Plus unit. I hope if this is something you need for test and inspections, you will find it useful.https://dmmcheckplus.com/technical-information#4f5b7f37-0b36-4ad2-a777-95b1229cdd4e

author: aronake
author_rank: Frequent Contributor
timestamp: March 06, 2025, 07:40:58 pm
content: For the data in the calibration report you send with the dmmchecker, do you adjust that for the error in the 3458a you use, or just use the reading from the 3458a in the calibration report?

author: Kean
author_rank: Unknown
timestamp: March 07, 2025, 04:40:04 am
content: Very good to highlight that you make these available, but I suspect making the historical calibration certificates available would also be helpful.If you alternate calibrations on your two 3458A, not everyone is going to have a unit that was tested on the 3458A with the latest posted cal certificate, nor know if adjustments were made as part of the cal.I'm not an owner of a DMMCheck Plus yet, only a rather old DMMCheck unit.

author: J-R
author_rank: Super Contributor
timestamp: March 07, 2025, 07:46:43 am
content: I don't see how it could be of any use in this case to consider the error or the historical certificates of the 3458A. The DMMCheck Plus doesn't remotely have the accuracy, nor does the calibration certificate even list more than five digits of resolution (except for frequency, which is trivial for the cheapest counter anyway). It's fine for checking 50,000 count DMMs or maybe a digit beyond that after a fresh calibration, but not really any more. For example, the 0.007% 5V DC could be between 4.99965 and 5.00035. AC values are only listed to four digits.

author: ap
author_rank: Frequent Contributor
timestamp: March 07, 2025, 09:52:01 am
content: Even with the low accuracy of this Reference, it is not clear to me how commercial customers could use these items for internal calibration purposes, given there is no datasheet (t least I could not find one) identfying coefficients for aging or temperature or the like. So in a traceability chain, there are major gaps from my perspective, the cal certs allone will not help much at all.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 07, 2025, 10:49:12 am
content: I see a rather limited need for the cal certificates. The DMMCheck Plus is only provide a few test points and could thus not be used for a full calibration. So if one needs a formal calibration for commercial reasons one would still send the meters to a proper cal lab. It is more an extra check and maybe a little more for a few ranges. Only few DMMs have calibration points at 5 V and 1 mA.Another problem is that the AC part is using square waves, while offical calibrations and relevant accuracies are with sine waves. The extra harmonics and higher frequency content and high slew rate can mess with some meters.The AC reading is of limited use and may depend on the meter internals, especially with the more lower end models with limited bandwidth. The meter can be perfectly OK and still read the square wave wrong or as a rare exception be off enough to compensate the effect of a square wave. With quite some meters it seems to work though. So maybe at least good to see of the meter under test changes over time.The square wave function also means that the 3458 specs don't directly apply - though this meter is likely pretty accurate still.Getting reliable data for the drift specs is a tricky thing. This is usually just a reasonable guess and only with time (e.g. getting data from many units calibrated after some 2 years or more) one would have real data to check.

author: IanJ
author_rank: Unknown
timestamp: March 07, 2025, 11:19:29 am
content: It's a DMM Checker, not a calibrator. The technical page quite clearly says what its use case is.Albeit the link off the home page could be a bit misleading.Ian.

author: Kean
author_rank: Unknown
timestamp: March 07, 2025, 04:19:19 pm
content: I agree with the above points, but if someone is asking for traceability I just thought it would help the to have the matching report for the unit and time frame of the document supplied with the device.It may not make sense from a metrology PoV, but Ross mentions in the video that businesses like cardiac imaging labs, avionics shops, auto manufacturers, etc asking for this info for validation by inspectors.Obviously (I hope) the inspectors are not going to be looking for 8.5 digit precision, but want to see some traceability to tick a box on a checklist. I would think that might include a cal report for actual equipment that matches those listed on the document - i.e. model, S/N & cal due dates. One for a different S/N or later date may be rejected.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 07, 2025, 04:37:30 pm
content: A cal report just after the meter was used would be OK and could be even better than a cal certificate before. This is especially when not adjustment was done or values before adjustment reported.For getting tracability it may work for the actual DC range. For AC, one can not really trust it very much unless used for square waves.

author: bdunham7
author_rank: Super Contributor
timestamp: March 07, 2025, 05:08:48 pm
content: Quote from: rkeller on March 06, 2025, 02:40:22 pmUnfortunately it appears that 3 out of the 5 certificates that you list are expired. Two of those may be unnecessary depending on what is written on the DMMCheck certficate, but still there's no point in keeping expired certs posted.

author: J-R
author_rank: Super Contributor
timestamp: March 07, 2025, 10:14:30 pm
content: I don't think the certificates are expired. Some TE won't require yearly calibrations. The 34470A has a 2-year accuracy spec listed, for example, which is plenty good for sanity checking the 3458A. (I'm assuming that is how it's being used.)

author: bdunham7
author_rank: Super Contributor
timestamp: March 07, 2025, 10:48:38 pm
content: Quote from: J-R on March 07, 2025, 10:14:30 pmTwo of the certs are from 2019.As for the Keysight, yes there's a two-year spec but I'd prefer to see that interval explicitly on the cert (or alternatively, no date) if I was mostly interested in paperwork for inspectors. I don't have relevant experience here so perhaps I'm off the mark. However, it is interesting when you actually do some tracing of the "traceability" everyone seems to want. Besides the interval issue, the calibration was done using a Fluke 5520A that itself was past the year mark from calibration. They list a due date of 2 years, but I don't see that supported in the manual. In any case, that means they're using a calibrator with a 1-year uncertainty (10V) of 14ppm, and beyond that year to boot. The meter itself has a 1-year spec of 18ppm, so unless the 5520A is claimed to be "characterized" IDK how that flies. From the cert:Unless stated otherwise; the expanded measurement uncertainty of the measurement process does not exceed 25% of the toleranceallowed for the individual characteristics measured,No mention of the 1.285 TUR.I do agree with you that this is all still good enough for a 70ppm DMMCheck Plus, at least unofficially. I'm not so sure the paperwork is good enough if someone digs in.I'm also not quite sure how you can use the DMMCheck Plus in a way that requires certificates unless you're someplace that just has a blanket policy that every instrument of any kind must have current paper. Perhaps someone can provide an example of such a use.

author: CalibrationGuy
author_rank: Unknown
timestamp: March 13, 2025, 02:51:48 am
content: I always thought this device was a quick and dirty way to check if a DMM was working. For this use, it works well. It's not a calibration reference as was pointed out above. Still a useful device IMHO.TomG.

author: J-R
author_rank: Super Contributor
timestamp: March 15, 2025, 12:26:00 am
content: The DMMCheck Plus can be used in any manner the buyer wants to use it, but of course with limitations. Previously I pointed out that you could directly get 100mV to 5 digits DC (AC to 3 digits-ish) from the current source and the 100 Ohm resistor.With the various calibrated components provided, you can check your equipment and use transfer standard principles to continue your checks well beyond what is immediately apparent.