An ac Resistance Bridge and Temperature Controller

Abstract

A solid state temperature controller is described which is capable of maintaining constant temperature within ±10−6 K at 1 K. The circuit is self‐contained and has been used with carbon and germaniumresistancethermometers over the range from about 15 to 0.03 K. Bridge balance and heater current are metered, and monitor outputs are included for an oscilloscope display and a strip chart recorder. The bridge circuit is a unique configuration which allows fully guarded cables to the thermometer and higher frequency operation (500 Hz). The control circuit is dual action with separately adjustable integral and linear proportional feedback. Up to 200 mW of control power is available.