50 Microdegree Temperature Controller

Abstract

A temperature controller has been developed using a platinum resistance thermometer in a bridge with inductively‐coupled ratio arms. It is capable of maintaining water bath temperatures constant to within ±25 microdegrees Celsius for 24 h in an environment varying as much as ±1.5°C at any temperature from 18 to 28°C. The sensitivity of the controller approaches the theoretical limitation imposed by Johnson noise. The design makes possible control dials which are direct reading in °C.