Electronics > Projects, Designs, and Technical Stuff
Fluke 731B Voltage Standard Restoration and Mods?
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TERRA Operative:
Yeah, I'll measure the charge current once it's all back in one piece and adjust as needed.


This morning I had a poke at the resistors. I found most of the carbon composite resistors were bad as expected. One on the reference regulator board was at exactly 10% out of spec for a 5% part, and the 8.1K on the power supply board was reading 9.2K... Two others were reading right at the limits of their tolerance, so the lot were replaced with 1%, 50ppm metal film resistors.

I checked the rest of the resistors (Except the hermetically sealed and precision ones) and they all measure spot on.

Also, the capacitor on the PSU board was reading bad on my LCR meter so it was replaced too, better safe than sorry.


I currently have the battery pack on charge so tonight I'll reassemble the unit and fire it up and let it settle for a couple days then start tweaking the adjustment pots. :)
Kleinstein:
For the battery pack, especially with NiMh I would consider an extra switch, so one can reduce the charging current from normal to a low current to just stop self discharge. So if one used on battery for a long time reduce the current.
TERRA Operative:
I'll have a think about adding a switch, although by the time they need replacement it'll probably be getting lipo's or something anyway. :D


So I ran it for a day to let it settle then hooked it to my 34461A multimeter for a day with a set of Pomona low EMF leads that I added a shield to, to see how things look.

I can get the voltages pretty much spot on to the extent that my 6.5 digit multimeter will show, except the dial is a little out. It seems it's a little lower than what is shown on the counter. I'm hoping I can tweak the position of the counter dial on the shaft of the pot to 're-zero' the mechanical stops so they are properly matched and then have it come into spec. As it is now, I don't quite have enough range on the cal pot to pull it into line.

Anyway, for now, a pic of the histogram after a day of running on the 10V output in a non-airconditioned room. :)



[EDIT] I just ran through the calibration again and it seems I probably don't have to adjust the knob etc. It might have come good.
HighVoltage:
Nice, that is a fist good confirmation that your unit is stable in the short term.
I had some drifting much more !

TERRA Operative:
Alrighty, I think I got me a winner winner chicken dinner.  8)
I had it running all day on the 1.018v range, check out the results after 100,000 samples in my non temperature controlled room. :) Doesn't look too bad to me.


I'll do the same with the other ranges to make sure it's as spot on as I can get it and I think I might have this unit sorted out. More screenshots to come!
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