On another note, I'm also trying to cobble together some resistance transfer standards for the club.
I got lucky on ebay and scored a GenRad 1434 for super cheap
which we can use as a donor for our resistance transfer standards!The 1434 appears to be a later, cost-saving model compared to the 1432 and 1433:
- The case is physically smaller.
- They pulled some clever tricks with the rotary switch to get away with only 6 resistors per decade (see schematic).
- Mechanically, the switches are vastly inferior to the older models.
My 1434 arrived with no knobs, one of the switches was stuck, and a few others are not so easy to turn. The resistors look fine, but mechanically, this design does not appear to stand the test of time. So its a perfect donor for our club!
Each decade has two ceramic cards with three resistors each, of a 2-value (20R, 200R, 2k, 20k, 200k). Through clever switching, they can turn 6 2-values into 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10-values.
This is ideal for our desired 1, 2, 3-value transfer standards, as we can simply parallel 2 of the 2-values to make a 1-value, then put that in series with the other 2-value to make 1, 2, and 3.
The 200k resistors follow the same scheme, but are on individual bobbins rather than cards.
These cards are just the right size to fit into the smallest water-tight aluminum case which Hammond makes, the 1550WQ. I'll order some of those along with some silicone oil, and include a thermistor in each case. I think we can get away without active temperature control for these, as there should be enough thermal mass that the typical +/-1F swing of a typical air-conditioned lab should be smoothed out. I can also characterize the tempco of the resistors so that we can provide a correction curve using the paired thermistor.
I'm super excited!