A New Technique for Measuring Thermal Radiation

A new technique is presented for measuring thermal radiation. The technique was conceived to aid in the evaluation of the base heating experienced by rocket vehicles due to radiation from the exhaust plumes. The instrumentation, chosen for its ruggedness combined with high sensitivity, is derived from thin-film resistance thermometry as originally developed for short-duration test devices such as hypersonic impulse wind tunnels. A heat meter based on thin-film resistance thermometry functions on the basis of the sudden application of a heat pulse. In the present application, for which the incident heat flux is steady, the heat pulsing is accomplished by actuating a shutter interposed between the sensing element and the incident radiation. Sample gages have been built and subjected to preliminary testing. Attention has been given to the problem of compensating the data for departures from ideal operating conditions such as the finite opening time of the shutter, and also the possible two-dimensional pattern of heat flow into the substrate material of the sensor. In addition, a special method for recalibrating the thin-film sensor is presented and illustrated with experimental results.