Products > Test Equipment
Easy way to test the calibration of a DMM (Fluke 45)?
shapirus:
--- Quote from: Majorassburn on March 30, 2024, 09:40:12 pm ---Is the DMM Check sufficiently accurate to calibrate a Fluke 45? No F**king way and you know it!
--- End quote ---
Yes of course it is, albeit only at a single voltage value (5V). It's accurate to ±0.007% (DCV output) and it's aged and then adjusted to exactly 5.0V as measured by a calibrated DMM with 0.0008% accuracy.
Quite obviously (on second thought -- maybe not so obviously; how much more accurate should the reference be compared to the DUT?) good enough for calibration of a 0.025% base DCV accuracy meter. But if we were to speak about adjustment (alignment), then it wouldn't be suitable, as you'd need more than one reference voltage, and probably more precise one than 0.007%.
--- Quote from: Majorassburn on March 30, 2024, 09:40:12 pm ---I'm sick of your arrogant sideswipes about most of my posts as I try to be a good participant in this forum.
--- End quote ---
You see, the issue with your device is not the quality of the device itself -- it may very well be just fine and suitable for many applications -- but lack of information. To be better than the chinese sellers, you should at least specify what device was used to measure output voltage of each reference you sell (I believe you specified this in at least one post) and present a calibration certificate for that device. To be much better than the chinese sellers (and this will almost inevitably lead to a price increase), you need to measure and specify more data: long-term stability, temperature stability, noise level etc. Aging them will also be a plus.
The value of a voltage reference is not so much in its components and design, but in the reference to which its output voltage can be linked. This is an important aspect where the DMMCheck Plus is good and chinese references are poor.
bdunham7:
--- Quote from: Fried Chicken on March 30, 2024, 09:49:15 pm --- assuming shipping is within the United States and available reasonably, which it should be through whatever freight forwarder service I use. I can include the return label in the box.... I am curious about what equipment you have in your lab that you might test it with, so I can gloat about know to what standard it's been calibrated to.
--- End quote ---
I'm in California and I'd recommend UPS or USPS with good packing. FedEx seems to be air-dropping stuff right from the plane from the looks of the packages.
As for equipment, not much to gloat about. I use an assortment of things to get the stimuli needed and a Fluke 45 is at the beginning of the area where things get slightly challenging. I've managed to calibrate 6.5-digit meters that later passed a 'real' calibration without adjustment, but in reality that's a stretch. The ideal situation is to have a good enough uncertainty ratio (TUR) that you can adjust the meter to within the limits of its short term stability. On your meter I would use:
Fluke 5100B multifunction calibrator, repaired and calibrated by me. 50ppm DCV basic accuracy, but no cert.
Fluke 8846A 6.5-digit DMM, calibrated by Fluke (cert attached below)
Fluke 5220A current amplifier, calibrated by Transcat (but more than a year ago) no cert available as I just have the sticker.
Fluke 8506A Thermal-RMS DMM, AC ranges informally calibrated by using a 5200A with an in-cal 3458A in parallel. This meter has a 1-year basic spec of 200ppm on AC and it probably is within that, but it only needs to be somewhat close in order to be more than good enough. In reality this is overkill, but I have it and need an excuse to use it.
A set of L&N NBS-style standard resistors from 1R to 1M.
Siglent SDG2042X signal generator
I use the calibrator as source for most ranges and then one of the DMMs in parallel (or series for current) to characterize the 5100B output. IOW, I fine-tune the 5100B using the more accurate meter. The Siglent AWG is for the 100kHz frequency test. For resistance, the decade resistors in the calibrator are accurate enough for your DMM and I'd check them immediately beforehand with the 8846A.
I've also attached the calibration procedure for the service manual. You can look at each test or adjustment point and see what the tolerances are and then compare them to the tolerances of the calibration equipment. For example, the third peformance test point is 900.00mVDC and the tolerance is +/- 290µV. If you look up and calculate the tolerance for the 8846A (1-year spec) at 900mV, it is +/- 30µV. And so forth. Those are good ratios, certainly good enough that I'm confident that your meter will be accurate, but probably no bragging rights.
bdunham7:
--- Quote from: Majorassburn on March 30, 2024, 10:33:46 pm ---But, you seem to have a bug up your ass about some of my devices that I offer on eBay.
--- End quote ---
I'm not claiming that you are dishonest or that your devices are overpriced, but rather that you don't seem to fully understand where they would be appropriate and where they aren't helpful. You're starting with a 0.05% device and trimming it to some unstated uncertainty and not further characterizing it or indicating how stable it might be over time. The descriptions and claims just aren't very precise. Your listing says 10.000V in one spot and 10.0000V in another. The maximal implied precision of first might be just adequate for a sanity check on the Fluke 45 if it were perfectly stable. The second claim of 10.0000V is preposterous if you are implying that level of accuracy with that device. If you trim it to that number using a particular meter or method, you should specify those particulars and give some idea of the actual uncertainty. Otherwise your specs are misleading, even if you don't intend them to be.
The problem in the context of the OPs issue is that when you have a particular device that you have doubts about, checking it with another device of similar uncertainty and no independent verification just leads to more uncertainty--if they disagree you just have two things that you're not sure of. In this case, your device is probably good for spot-checking the Hioki, but not adequate for the Fluke, IMO.
That's about the whole issue I have in this context. I realize it is a very inexpensive device and it would be silly to hold it to the same standard as a VREF10 or even a DMMCheck, but that also implies that its applicability is more limited. If you want a better idea of how your device performs and aren't ready to start logging temperature vs voltage and so forth, send me one (I'll send it back) and I'll give you a chart. Maybe it will do better than anyone thinks.
Fried Chicken:
To be honest, if I have two units with agree with a calibrator, and a fluke that doesn't, that definitely points to the fluke being problematic. It would serve to see if I need calibration... assuming my other voltmeter devices are accurate enough.
shabaz:
Very kind, generous offer to unofficially calibrate.
Just to put some sample numbers out there, for the AD584 cheap references (sub-$10 on AliExpress), by chance, a friend and I have both measured these devices (one sample each, purchased separately at different times) using two separate DMM6500 meters.
The label on it, claiming to have been measured with HP 3458A, is, of course, completely untrue (unless it's a completely broken HP 3458A!). They probably used (at best) a 6.5-digit meter, perhaps not even calibrated, and even then, they have typos in the printed values (the label on mine had a noticeably erroneous extra digit for one of the values!).
However, on the plus side, it turned out that the nominal voltage values (2.5V, 5V, 7.5V, 10V, were actually close enough to the real values, that it's very likely that one would be able to tell if that 0.02V discrepancy you're seeing between multimeters is a problem with one meter or the other, or both. In other words, a 20 mV discrepancy should be identifiable if it's present at one of those four voltages (2.5/5/7.5/10V).
Beyond three digits, you can't really rely on it with no measurement with a known calibrated instrument. Nevertheless, for the price (under $10) with no further measurement, it is a crude finger-in-the-air type of check if absolutely nothing better is available.
Just in case this helps, this was my sample result:
Label My measurement
------- ---------------
2.49954 2.49963
4.999501 4.99964
7.39875 7.49899
9.99823 9.99854
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