Had a bit of a distraction with getting the Pi onto the wifi here and then dealing with the linux-gpib driver, but the logging is setup and is now taking measurements every 12 hours. Hopefully I'm correct in assuming that ACAL needs to be run before each measurement to update the DCV 10 Gain value (CAL72). The code I'm using is here:
https://github.com/dkozel/voltage_reference/blob/master/warm_up_logging.pyHere is the first 12 hours of data. The DMMs were turned on about four hours before the start of logging so definitely way to early to care much about the numbers. I'll leave this logging running until at least the middle of January as I have some other work coming up that will be distracting.
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
DMM "22"
Time | T Celsius | 10V Gain | 40k Ref | 7V Ref | 10V Gain ppm |
2018-12-04T18:04:59Z | 46.1 | 0.985288471 | 40001.864 | 7.08983721 | 0 |
2018-12-05T06:04:59Z | 44.3 | 0.985288206 | 40001.864 | 7.08983721 | -0.269 |
DMM "23"
Time | T Celsius | 10V Gain | 40k Ref | 7V Ref | 10V Gain ppm |
2018-12-04T18:05:00Z | 45.9 | 0.987604634 | 39999.1402 | 7.09641088 | 0 |
2018-12-05T06:04:59Z | 43.6 | 0.987606166 | 39999.1402 | 7.09641088 | 1.551 |
I have the DMMCheck board which I briefly used to check a few of the ranges, but I'll do so more methodically when I get the chance and share the data. I have a pretty precise SMU that I can use to generate test currents and voltages down to the ~50uV and ~100pA accuracy.
For the INL test (
Reference Thread, yes sadly the closets don't have a JJA (I did check just to be sure), but doing a relative comparison to each other does seem interesting. I'm guessing that I can use the above SMU as it is the stability rather than accuracy that is important and the noise levels are quite low on it.
For the Noise Test (
Reference Thread) That seems quite straightforward and I can run it during the 12 hour downtimes. Though I was already looking at getting a low EMF short and found that it's already been done for the 3458A by texaspyro (
Thread). But yah, this project is going to be expensive enough so I'll use basic copper wire and not loose a month waiting for PCBs!
![Tongue :P](https://www.eevblog.com/forum/Smileys/default/tongue.gif)
The input bias current link is interesting, thanks for linking that lukier! Without spending too much time thinking about it, it seems like we'd want to shield the jumper cable as it runs the length from the HI terminal to the ground point, maybe some scrap coax and ground both center and shield at the back and just the center at the HI?
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif)
The capacitor option is interesting as it could be a through hole component mounted just between the HI and LO terminals(?) keeping stray fields from being a potential issue.
tggzzz! Yes, definitely I'd enjoy meeting up sometime next year for a comparison and chat. That's a fun collection of items for sure! I'm a bit behind on the LTZ build due to some BOM confusion (so many details!), but February/March I should have them built and warmed up.