[volt-nuts] BECO 312A impedance bridge

[Dick Moore]

I picked up this Brown Electro-Measurement Corp bridge recently and have made a few small repairs and adjustments. I've only checked resistance measurements so far -- I don't have precisely measured caps or inductors yet to check reactance measurements.

Using the DC generator and an external null detector, I get quite excellent resistance results -- better than 0.05% on all seven ranges. However, using the internal detector amp, the errors are fairly significant, especially on high resistances. The detector is obviously loading the bridge. 

I have no schematics for this unit and haven't been able to find any on the web. Anybody have the circuit for the detector in this unit, or one similar? It's all discrete, no ICs, and nothing inside cans -- it's all out in the open. I have the schematics for the ESI 250DE, which is similar in that the detector is all discrete, but the similarity seems to end there... but more checking is needed.

Best,
Dick