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| Easy way to test the calibration of a DMM (Fluke 45)? |
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| Fried Chicken:
Here's a guy with a Fluke 8842a and a cheap chinese voltage standard: |
| Fried Chicken:
--- Quote from: bdunham7 on March 30, 2024, 11:54:15 pm --- --- 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. --- End quote --- I'll send you a PM tomorrow. I think I'll take you up on this offer! Would definitely be thrilled to see the process documented! Happy Easter! |
| J-R:
The problem with the Chinese eBay references is that you can't really apply any trust to them. Sure, one person might get one that is OK, but the next may not be. Or you could have blatant fakes, as has been shown already with the copied calibration labels. Also, a random video of someone showing how close their DMM is to a reference can be suspect because it's possible they used it to calibrate the DMM earlier and are hiding that fact. You just can't be sure. Compare this to the references from Doug and Russ where they have been active here for a while and their products are well regarded. Although really the King of hobby DCV references is the PDVS2mini in my opinion. Really hoping it comes back soon so I can get a second one. I also plan to get a second 10V reference from Doug because his updated model has some great improvements. I have quite a bit of equipment that can leverage a 10V calibration point. But the bdunham7/Majorassburn conversation has got me thinking that what the hobby really could use right now is a budget-friendly calibration service. There is a gap between getting a professional calibration and trying to do a DIY calibration with references on hand. I don't see the USA Cal Club being a solution since it's more in the metrology space. |
| alm:
--- Quote from: J-R on March 31, 2024, 04:58:19 am ---But the bdunham7/Majorassburn conversation has got me thinking that what the hobby really could use right now is a budget-friendly calibration service. There is a gap between getting a professional calibration and trying to do a DIY calibration with references on hand. I don't see the USA Cal Club being a solution since it's more in the metrology space. --- End quote --- The problem I see that this is capital and time intensive. I would imagine buying all the equipment that bdunham7 listed now might cost you maybe $5k, if not more. And calibration of even just the 8846A (which will give you uncertainties that are plenty good for 4.5 digit like the Fluke 45 but not for 6.5 digit like HP 34401A) will be a few hundred USD per year. This figure can easily get into thousands per year if you need to have multiple pieces of equipment calibrated. And also, correctly if I'm wrong, I'm guessing that bdunham7 has not set up an automated calibration for the Fluke 45, so calibration, and particularly adjustment, might easily take hours in changing connections and settings, waiting for things to stabilize, etc. Expecting someone to do this regularly for a low fee is a lot to ask. Would you like to be spending every Saturday doing calibrations for say $100 per day? Even the production of products like the Geller Labs voltage references, DMMCheck Plus and PVDS2Mini does not seem very sustainable given how often the stop production or change hands. |
| robert.rozee:
one could probably go a long way with just a DIY hamon divider http://conradhoffman.com/HamonResistor.html and the raw output from a simple LM399 reference. first send the LM399 off to someone with a good 6.5 digit meter to measure it, then use the LM399 and hamon divider to calibrate low DC voltage ranges at 7v, 700mv, 70mv. if desired, 70v and 700v points can be calibrated using the same gear plus an adjustable HV supply and a little creativity. i dare say resistance ranges can similarly be calibrated using similar methods to scale up/down and just a single precision resistor that has been measured with a good 6.5 digit meter. sending off a small PCB (containing LM399 + CC source) and a single resistor through the post should be relatively cheap, and the time expended by the recipient making measurements relatively short. cheers, rob :-) |
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