Low-Temperature Adiabatic Calorimeter with Automatic Shield Control

The design and operation of an adiabatic low-temperature calorimeter employing a somewhat different design of automatic shield control is described. Thermocouple difference is sensed by a dc μv amplifier, which is followed in the circuit by a recorder-controller and a Leeds & Northrup Series 60 (current adjusting type) control unit. The output of the latter is used to control the voltage across the shield heaters through a Westinghouse ``Magamp'' saturable reactor. This design has been used successfully with a conventional low-temperature adiabatic calorimeter (50-ml sample size). In most cases the recorder showed no variation from zero (±0.002°) during heating and equilibrating periods, while momentary disturbance at ``on'' and ``off'' was less than 0.05°.