High-precision low-cost temperature controller

Abstract

A temperature controller is described, capable of maintaining the temperature of a properly constructed thermostat constant to within +or-5 mu K for an hour and 40 mu K for a week in the range from about 280 to 320K. It uses a thermistor as a sensing element in conjunction with a simple AC Wheatstone bridge. The electronic circuits of the controller, consisting of a lock-in amplifier, a proportional, derivative and integral regulator and a power stage, are built of low-cost, commonly available components. An extension of the temperature range of application is straightforward, but will lead to reduced accuracy.