SIMPLE INEXPENSIVE LIQUID HELIUM TEMPERATURE CONTROLLER USING INTEGRATED SEMICONDUCTOR CIRCUITS

We describe a controller for regulating the temperature of a pumped liquid helium bath. The controller is a considerable improvement over previous controllers in that it is much simpler and less expensive. These improvements are due mainly to an uncommon direct-coupled alternating current circuit, and to extensive use of the recently introduced integrated semiconductor circuits. The controller operates by measuring the resistance of a carbon radio resistor immersed in the liquid helium bath, and then feeding back a proportional correction current to a heater. The controller will control a bath to within 100 μK over a period of 20 min, at 2.1 K, and could be used to control the temperature of a copper block over a wide range of temperatures. © 1969 The American Institute of Physics.