Electronics > Metrology

Data Precision 8200 calibrator - repair and other fun stuff

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Rax:

--- Quote from: branadic on July 23, 2023, 06:00:35 pm ---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.

-branadic-

--- End quote ---
branadic,
I may have missed it, but did you intend these to be compared with the "before" measurements? If yes, can you please point me to where they are available?
Than you.

branadic:
It was way larger before, more in the 10 µVpp range, but I don't have an image of a measurement at hand.

-branadic-

Rax:
It's been a while, y'all.

I have a second 8200, and got around to adjustments this weekend. It's a much cleaner unit and it seems to be working well overall. One issue I'm finding, though, is that I'm unable to get it to 70V when adjusting it per 4.2.3-9. The adjusting effect is very small, and I'm pretty sure I'll run out of range before I get to within 100uV of value. I'm typically finding an adjustment like this to be very close to the original pot position - more like a trim than a finger-spinning workout. This isn't acting like that, it barely moves in output value with vigorous spins of the pot adjustment.

I posted on this on the Repair group: https://www.eevblog.com/forum/repair/data-precision-8200-100v-range-out-of-pot-range-during-adjustment/.

Thank you for all input!

branadic:

--- Quote ---he lower reference noise would mainly make sense together with a change in the OP-amps (Z6,Z14,Z19) for lower noise.
--- End quote ---

As far as I understand you suggest OP177 for Z6, Z14 and Z19 and to remove C19 at Z6, is that right?

-branadic-

Kleinstein:
Yes these 3 OP-amps will contribute to the noise. The original AD517 was a good OP-amp at it't time, but is still pretty noisey (2 µV_pp for 0.1 - 10 Hz). This may be acceptable for a LM399 or similar reference with some 5 µV_pp on its own, but an upgrade would make sense with an ADR1399 reference. With a change in the reference one would need to readjustst the voltage anyway and the different offsets should be no issue.
C19 is odd in the circuit, it reduces the phase reserve and not all OP-amps may like it - here it may be worth checking at least to check if it works better without or possibly oscillates with C19.

An OP177 would be a candidate that is also awailable in DIP.

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