Device for the measurement of transient surface temperature changes

Abstract

A device has been built to allow measurement of transient surface temperature changes with fast time resolution and high temperature sensitivity while absorbing negligible heat energy from the object whose temperature is measured,, The device will measure temperature changes of surfaces as small as a few square millimeters, with temperature changes comparable to one milli-degree, with risetimes comparable to one millisecond, with extraction of power from the target comparable to ten nanowatts, and with accuracies better than 10 percent. The device does not cause local heating or cooling of the target, so it is not necessary that the target be stationary. The device is built around a radiation gas thermometer called a Golay Cell. A Golay Cell has an internal incadescent lamp for excitation. In the device developed, that lamp is removed and a filtered real image of an incandescent filament is produced where the physical filament had been. A filtered image effects the elimination of major thermal gradients in and around the Golay Cell, orders of magnitude reduction in visible and infrared radiation emitted from the head of the detector, and increased output linearity. The target whose temperature changes are to be measured is optically coupled to the Golay Cell head by a conical reflecting surface. The differential current output of a Golay Cell is an analog of the incoming radiation differential with great time distortion. An electronic circuit was built to process the analog current output of the Golay Cell. That circuit blocks the direct current component of its input, reduces input drifts, allows zero level reset, improves high and low frequency response, limits noise, and linearly amplifies. The voltage output of this circuit is an analog of the temperature changes of the target with properties as described above.