UNIPAN 251 DC Nanovoltmeter

[doktor pyta]

Hi,
I have the UNIPAN 251 DC nanovoltmeter unfortunately without any schematics and manual.
It was made in Poland in the 80's. I was informed that most of the units produced were sold to USSR.

The device uses Airpax electromechanical chopper. It is using only semiconductors (no vacuum tubes inside).
The design reminds me of Keithley 146 or 147 nanovoltmeter.

The device has one problem. On the whole uV range id shows readings that are half they should be.
For example I'm applying 100nV and the reading is ca. 50nV.

I figure out that the 1 ohm resistor in the nanovolt input feedback net has higher value than it should. The reason for that was old crimped copper to copper connection. When I crimped it harder with my tweezers it hepled but only for few days.

So, what would You suggest to solve that. Brand new crimped connection or some other technique?
PS. Could an owner of Keithley 146...7 send a picture of the input stage?


I'm placing few pictures for those who are interested.

[Mickle T.]

Very impressive design. Thank you!

[TiN]

Connections going to uV/nV switch are really corroded. Perhaps remove them, clean them well (maybe etch copper a bit to get shiny fresh metal?) and connect back.

Interesting device, thanks for posting.

[Mickle T.]

Front panel design, input connector, voltage ranges - all are identical to Keithley 148.

[doktor pyta]

Notice the weird 3 -terminal component connected to the uV/mV switch. It is the epoxy potted 1R/1k divider made so to equalize temperatures of resistors and the connection between them ! Additionally it is covered with aluminum sheet.

It can be a good point to make DIY nanovolt divider...

Oh, what do You think about etching, cleaning, crimping connections and finally covering it with the urethane or Plastik 70 to prevent copper oxidation ??