Electronics > Metrology

Data Precision 8200 calibrator - repair and other fun stuff

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--- Quote from: branadic on March 23, 2023, 05:58:27 pm ---I have upgraded AN3200 with an over 8000 h pre-aged ADR1399. I had to adjust R7+R8 from original 1.14kΩ  to 1.7kΩ to have enough of margin left for adjustment on the 20Ω pot.

--- End quote ---
I'm still interested in details on the resistors values revisions.

Have you seen any ill effects with doing this on the linearity of the instrument? Put differently, have you had to tweak the octade adjustments (within the "metrology calibration" procedure - R33, R30, etc.)? If not, this seems to be a pretty effective and relatively "low impact" upgrade to this unit.

R12 is part of the field calibration procedure, so I don't think that has bearing on the linearity of the instrument, and is obviously an expected adjustment to do given the change in the reference (in addition to the other resistors changes you mention).

Changing the reference and accordingly adjust R7,R8 (or R9) and R12 should not have  an effect on the linearity. The change of R8,R9,R12 is to bring the ref. voltage seem by the divider back to the old value. So the octal divider chain would not see if the reference voltage changes (e.g. 7 to 6.9 V). The main change would be a slight higher current to the reference.

It is still a question if this would really be an upgrade worth while: the ADR1399 is lower noise, but the old LM299/LM399 is usually well aged, depending on how long the unit was powered on.
The lower reference noise would mainly make sense together with a change in the OP-amps (Z6,Z14,Z19) for lower noise.

R7 = 3.01 kΩ was replaced by 1 kΩ so roughly the same 3 mA through the zener as before.
R8 and R9 were replaced to the value given above to get back the adjustment range of R12. The noise went down significantly, even though Z6 wasn't replaced yet. I have an OP177 sitting on the shelf, but am not tempted to install it at the moment, also due to missing TO to DIP adapter and I don't like a dirty bodge to fit it in.
And as stated too, the ADR1399 saw a burn-in for over 8000 h before.


After having two units here to play with and assessing different things, I think it's very important for any of these to have its offset adjusted (4.3.3 in the manual).

It's technically part of the "metrology standard adjustment," but I don't think it affects anything on the linearity etc. of the unit. I may be wrong, but I think they should have included this in the "field adjustment." My standard tackle on these is currently the offset and the field adjustments. Once these steps are done, I'm finding this very well dialed in.

I've found the offset to be very high on these when they get to me - hundreds of uV - due to aging, lack of maintenance, etc. And this residual can throw all sorts of mayhem in the measurements, adjustments, etc.

I was asked to share some noise measurements with replaced reference, outputting 10 V.
Notice, the opamps are still original and have not been replaced. Please replace mV by µV and you end up with 3 - 4 µVpp.



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