| Products > Test Equipment |
| Easy way to test the calibration of a DMM (Fluke 45)? |
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| Majorassburn:
--- Quote from: bdunham7 on March 31, 2024, 01:12:18 am --- --- 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 --- snip - 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. snip - 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. --- End quote --- OK, Thank You for that advice. Let me respond: 1) For your first comment about the 10Vref and trimming, the "10.0000" you refer to was a typo on an early eBay ad where that ad had both 10.000 and 10.0000 in the specs. That was corrected several ads ago to read "10.000". So, you are correct about the typo conflict. 2) I built a typical 10Vref, like my eBay ads, and that device is trimmed to an actual value of 10.0000 with a new DMM6500 that I have occasional access to. That device is then "compared" to my new Sig SDM3065 and the eBay devices are then trimmed to 10.000 based upon the Sig. Crude but very effective, so far. Read the eBay feedback from those who have bought them and tested them for accuracy. I'm not saying that's the best way to operate but at this point, it keeps costs low and makes the low-end buyer happier than spending $250+ for a DMM Check, etc. if they are even in stock. Not knocking DMMChecks but whenever I wanted to buy one in the recent past they were never available. 3) As for the SPECS issue, I agree with you that my devices are very short on "specs" but my devices are also very short on CLAIMED specs, like so many phony Chinese devices. I don't want a volt-nut to buy one of my devices and then scream that it missed listed specs by .0005ppm after it was lit up in an oven for 6 months. :-DD The specs for my devices are the data sheet from Linear Tech (Analog Devices) for the AD1236-10 voltage ref IC that my device is based upon. I include the data sheet with every sale so that each buyer can decide how much faith he/she/it :scared: should place on the long-term accuracy/usability of the device. Of course, I could list the fact that in the trim circuit, I use all selected 1% 15-25ppm metal film resistors but the Bourns trim pot blows that up into another spec argument, right? Or, I could hand trim each device with selected low-ppm resistors and eliminate the easy-adjust trimpot. Hmmmm. Now, you may begin to appreciate why I purposely avoid "over-specifying" my devices. For those serious buyers, like yourself and myself, who eat & sleep specs before we buy stuff, my devices amount to no more than curiosity or novelty. But, to anyone who wants to simply and quickly and affordably verify the DC or AC or Resistance accuracy of their DMM, I honestly believe that my devices fulfil that kind of need. Do I compare my devices to a DMMCheck or other superior engineered devices? NO, not at all. I'm not in that league. I'm making hobby-grade stuff for amateurs, homeowners, DIYers, students, hobbyists and guys like us that now have something new to talk about and slice and dice in forums. :-DD :-DD Here's what I would like to do: I'd like to start a thread where I list reasonably concise specs for each of my hand-made devices and encourage fellow forum participants like you to evaluate, correct, criticize and comment on which would help me arrive at some happy medium in my ads. Where in this forum should I do that? What category? Test Equipment? Metrology/ (I love that category because there are no sane individuals there at all - I feel at home there just browsing!) :-DD Let me know what you suggest and I'll do it. Thanks and Happy Easter, all. |
| bdunham7:
--- Quote from: Majorassburn on March 31, 2024, 03:39:25 pm ---Where in this forum should I do that? What category? Test Equipment? Metrology/ (I love that category because there are no sane individuals there at all - I feel at home there just browsing!) :-DD --- End quote --- Just reuse this post with a little background added and post it in the metrology forum. I'm sure you'll get comments and some might actually be helpful. Include everything you've written here as I'd like to respond without cluttering up this thread any more. |
| shapirus:
...and I wish you good luck (without irony), because having yet another option for an inexpensive voltage reference is a good thing, especially if it comes with an honest specification which lists its parameters and allows to clearly understand the limits of its applicability. |
| Fungus:
--- Quote from: shabaz on March 31, 2024, 01:58:39 am ---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. --- End quote --- Those cheapo references on Aliexpress are a mixed bag. Some are genuinely measured, some aren't. Several people on EEVBLOG have ordered one and received the exact same "calibration"sheet. https://www.eevblog.com/forum/metrology/are-cheap-ad584-units-worth-it/msg920924/#msg920924 |
| shabaz:
Hehe yeah zero trust there with that sticker : ) I had the access to be able to test it against a known DMM, but most people purchasing that won't. I think it's fine as a quick check for those seeing large discrepancies (tens of mV) to try to narrow down which of the instruments is most in need of a health-check, and definitely expectations need to be low and not trust the device (at least not without confirming) much further than 3-digits (i.e. 2 decimal places) or so! |
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