Transient Response of an Intrinsic Thermocouple

Abstract

Where rapid heating is encountered, as in a prompt-burst nuclear reactor, a thermocouple with a rapid time-response is necessary to monitor the temperature of the specimen in question. Because all thermocouples have some mass, they cannot have an infinitely fast response. However, an intrinsic-type thermocouple has less thermal inertia than the usual welded-bead type. Thus it is a natural choice for the measurement of transient surface temperatures of conducting solids. In this report an analytical expression is obtained for the transient response of an intrinsic thermocouple. In support of the analysis, experimental data are presented which were obtained by means of a capacitor bank pulse-heating technique. It is concluded that thermocouple wires of small diameter and low thermal conductivity respond the fastest. As an example, a 1-mil constantan wire on a copper substrate produces 95 percent of the steady-state emf in 3 μsec.