Transistorized Liquid Helium Temperature Regulator

Abstract

A transistorized temperature regulator that is capable of controlling the temperature of a liquid helium bath to better than ±10 μ°K for periods of 20 to 30 min is described. The circuit employs a carbon resistor as the temperature sensing element and achieves its temperature control by varying the current supplied to a 200 Ω heater located in the liquid helium bath. Both a null meter and a heater current meter are incorporated in the design so that regulator performance can be continuously monitored.