Resistance Thermometer Bridge for Measurement of Temperatures in the Liquid Helium Range

A 33‐cps resistance thermometer bridge, suitable for precise temperature measurements in the liquid helium range, has been designed as a completely self‐contained unit. The amplifier has a gain of 120 db, band width of 0.3 cps, and input impedance of 10 kohms. With a power dissipation of 2×10⁻⁸ watts in the thermometer, resistance changes of 0.1 ohm can be detected. For a typical resistance thermometer this corresponds to a temperature change of 4×10⁻⁶°K at 2°K. Other features include high rejection of line‐frequency pickup, short recovery time after saturation, and a combination gain band‐width control which shortens the response time during preliminary balancing operations.