This week's acquired treasure was a Cropico ESC1 1V voltage standard.
The output voltages < 6.9V can be derived by a simple resistive dividers; I avoided a similar device with a 10V output on the principal that I didn't want an op-amp's infelicities to get in the way of stability.
After leaving it in the garage for a couple of days, then removing all the packaging on the driveway and dumping it in the bin, then washing my hands, using readily available "undiluted hand sanitiser" on the case, I was finally able to look at it.
The positive and negative points from the auction photos can be seen: more tape residue than expected, but a "reference standard not to be removed from the stds room" sticker. The worry was that this was a battery only device powered by 18 1.5 D cells on top of the box, and that they might have leaked and gone everywhere. Looking around the back shows a jack socket marked 23V-27V. I wasn't expecting that since Cropico expected non-battery supplies would introduce noise. Since I don't have a corresponding plug, I'll temporarily connect a PSU to the battery terminals. Later I may make a nice low-noise 723 pre-regulator.
Anyway, time to take the top off, and... no worries - as clean as a whistle.
And on the inside of the lid...
The internals show neat wiring and a passive filter right by the outputs. I'm not going to open the black box unless absolutely necessary - too much chance of disturbing something. And the front panel cleans up nicely.
So, does it work? A quick comparison with my Fluke 515 shows the 1V is within a few µV. Anything more will require careful experiments.
Overall:
- excellent, looks like a winner
- does anyone have any info on the PT100 socket; there's more than 2 wires attached
FFI, there's more info here:
https://www.eevblog.com/forum/metrology/cropico-esc1-electronic-standard-cell-a-look-inside/https://www.eevblog.com/forum/metrology/cropico-electronic-cell-power-supply/msg1254248/#msg1254248