Low-Level Thermocouple Amplifier and a Temperature Regulation System

Abstract

A breaker‐type dc amplifier suitable for measurement of thermocouple voltages as low as 10⁻² μvolt is described. Mechanically driven ``choppers'' operating at 40 cps are used to modulate the thermocouple signal and later demodulate the amplifier output. Both input and output are floating and may normally be operated connected to ungrounded circuits. Over‐all voltage gain is approximately 10⁷ while the zero error corresponds to less than 10⁻²‐μvolt dc input within five minutes of turning on. The amplifier contains only standard components and details of a suitable chopper which can be made in the laboratory are given. A temperature regulation circuit is described which is suitable for precision control of temperature in conjunction with a differential thermocouple. An indicated temperature match as close as 0.0002°C has been obtained with a single couple.