A self-compensating temperature indicator

The following paper describes a unique adaptation of the temperature sensitive magnetic alloys known as “calmaloy” to the cold junction compensation of thermocouple temperature indicators. It has been known for some time that certain specially prepared copper-nickel alloys possess the property of changing permeability linearly with temperature over very wide ranges. This peculiar function of permeability has been advantageously used for effecting temperature compensation on different devices, particularly watthour meters. The need has recently arisen of providing suitable compensation for millivolt meters used in connection with thermocouples for determining the temperatures of air cooled aircraft motors. It is shown that by employing the restoring torque on the instrument produced by a small vane of calmaloy in addition to the usual restoring torque of the spring, a very satisfactory compensation results. Curves are shown which illustrate the accuracy of compensation obtained and a detailed explanation of just how it is accomplished is also given.