Journal of the Society of Motion Picture Engineers (1930-1949)

Record Details:

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1950 INFRARED WITH ELECTRIC-FLASH 491 increased in size to handle the average power, it will have low efficiency, requiring in turn a higher average power input. When these conditions apply, it is advantageous to construct the tube of quartz which can be operated at a much higher temperature level than glass, and a compromise must be made between efficiency and power handling ability. For the CAA recorder, a small quartz U-shaped tube (see Fig. 5) was designed which had a reasonable efficiency and was able to handle the necessary power without overheating. Its size permitted the use of a very small reflector without sacrificing reflector efficiency. As shown in Fig. 3, its infrared efficiency is about 50% higher at 500 than at 1,000 v and hence a voltage operating level of 475 to 500 v was chosen. This voltage level has the advantage of simplifying the power supply design for an airborne application. The dimensions of the tube and gas pressure are such as to give reliable starting at this voltage. A special mounting base protects the fragile graded quartz-to-tungsten seals and fits into a standard Fig. 6. Schematic diagram of infrared electric-flash instrument recorder. fluorescent starter socket which locks the flashtube in place, but at the same time makes it easily removable. Adequate spacing for the spark lead is obtained by placing its termination well up on the side of the base. Using a Wratten 88 A filter over a small reflector, 4 in. in diameter, a Wratten 88 filter. over the lens, and infrared film, an input to the flashtube of 12 to 14 w-sec gives the illumination required for the recorder. Circuit The circuit (Fig. 6) has several features of particular interest. Inasmuch as the primary power source was to be an aircraft 12-v battery, one of three types of conversion was available: (1) vibrator, transformer and rectifiers; (2) d-c to a-c inverter, transformer and rectifiers; or (3) 12-v d-c to 450-v d-c dynamotor. Dynamotors are generally preferred to vibrators in aircraft and eliminate the need for transformers and rectifiers and therefore were chosen as the means