| Products > Test Equipment |
| Easy way to test the calibration of a DMM (Fluke 45)? |
| << < (25/29) > >> |
| bdunham7:
And for one final interesting thing before I leave this project for a bit, the calibration constants can be retrieved over the remote connection (RS232 in this case) and so I did. Here they are. You can see that the first six are off by amounts similar to the errors I'm seeing. IDK which way they work or whether they are the cause of the errors or if they are attempting to correct the errors. |
| Fried Chicken:
I am following this with interest! This is thorough work! --- Quote --- It is also the only meter I know of that has modern closed-case calibration but still uses a plain 6.3V zener (presumably a selected temperature compensated model) as a reference. --- End quote --- What do meters normally use? It's my understanding these DMMs are stable in their calibration once calibrated |
| Fungus:
--- Quote --- It is also the only meter I know of that has modern closed-case calibration but still uses a plain 6.3V zener (presumably a selected temperature compensated model) as a reference. --- End quote --- It doesn't really matter what the exact voltage is for digital calibration. All you need is something stable. There's no need for laser trimming to an exact value or anything like that. --- Quote from: J-R on April 05, 2024, 01:52:32 am ---It does seem a little odd that so many readings are low. --- End quote --- They're probably all related in some way. At the end of the day everything comes down to measuring voltage (Ohms, amps, etc. are all done by measuring voltage and using Ohms law). |
| CalibrationGuy:
--- Quote ---It doesn't really matter what the exact voltage is for digital calibration. All you need is something stable. There's no need for laser trimming to an exact value or anything like that. --- End quote --- It all comes down to your requirements. As an example, if you are using a 12bit DAC then a voltage reference trimmed to 4.096 Volts would be very convenient as each step would be 1mV, simplifying your math and eliminating scaling equations and their associated errors. TomG. |
| bdunham7:
--- Quote from: Fungus on April 05, 2024, 12:54:17 pm --- --- Quote --- It is also the only meter I know of that has modern closed-case calibration but still uses a plain 6.3V zener (presumably a selected temperature compensated model) as a reference. --- End quote --- It doesn't really matter what the exact voltage is for digital calibration. All you need is something stable. There's no need for laser trimming to an exact value or anything like that. --- End quote --- Sure, I'm not concerned about the value. However, either buried zeners with temperature compensation or on-die heating are used in most decent bench meters these days or else a bandgap reference for those on the lower end. For example, the 8808A which replaced the Fluke 45 uses an LM399 while the much older 8800A used the SZA263. The Fluke 45 is a 1990's product, not 1960's. The only digital meter I have with a plain temp-compensated zener is the 1968 era Fairchild 7000A which has surprisingly good specs--about the same as the 45--but needs a long warmup to acheive them. In any case, I've run the Fluke 45 overnight and it seems completely stable with no signficant tempco over a 3-4C range. Apparently the selected temp-comp zener does the job. |
| Navigation |
| Message Index |
| Next page |
| Previous page |