Thermoresistive radiation sensor response time employing electrical heating

The thermal time constant (/spl tau/) of a thermoresistive sensor is defined in terms of its physical properties such as mass (m), specific heat (C), area (A), and overall heat transfer coefficient (U) to the surroundings. Measurement of c and U by direct calorimetric methods may involve lengthy experimental procedures. The time constant determination using electrical heating introduces measurement error. An analytical formulation to demonstrate the origin of this error and a procedure to eliminate the same and determination of the values of /spl tau/, UA, and mc, are presented. Sensitivity considerations for the choice of appropriate sensor heating currents to minimize some of the measurement errors are also discussed.