Abstract

The video image of a geometrically simple target may appear to be complex if some component of the target is periodically varying at a frequency greater than the video frame rate. The presence of aliasing at above-frame-rate frequencies has hindered videography of high-speed, repetitive phenomena. We have developed a technique that allows such events to be imaged with an unmodified RS-170 imager (either infrared or visible). The system consists of the imager, a microcomputer, and a custom hardware interface to synchronize data acquisition. High-speed images are obtained by selectively acquiring data according to its phase shift with respect to an external reference signal, and by treating the imager as a high-speed, multiplexed line sampler, rather than as a low-speed, video frame sampler. We have used this system with an IR imager to study a number of heat-transfer problems, including combustion phenomena in a spark-ignited engine. The resulting images have a significantly shorter "effective integration time," which is % of the integration time for conventionally obtained IR thermograms, so thermal phenomena such as flame propagation and heat transfer in the piston head can be isolated.

© 1990 Optical Society of America