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1950 INFRARED WITH ELECTRIC-FLASH 493
slight reversal of voltage, thereby allowing the tube to deionize. The amount of reversal must be limited to a small value to prevent damage to the electrolytic discharge capacitors.
To prevent inverse output voltage from the dynamotor, which in turn would cause failure of the electrolytic capacitors, it is necessary to prevent operation of the dynamotor in the event that the polarity of the battery voltage is ever reversed. This is accomplished by placing a selenium rectifier in series with the coil of the main control relay RY-1 which prevents its closing if the polarity of the voltage is incorrect.
The cameras described previously have had new 12-v d-c governorcontrolled motor-drives installed to operate them at one frame per second to within an accuracy of about 1%. The nonreversal protection described above also prevents the camera motors from driving the film in the wrong direction.
Mechanical Design
Figure 7 shows the complete unit (total weight 18 Ib), which includes the power supply, camera, lamphouse assembly and cables. A test bank of instruments is also shown. The motor-drive, governor, and lamphouse are attached to the camera, but the lamphouse may be removed for side-lighting by releasing two small snaplocks. Slack cable coiled inside the motor-drive housing allows operation of the lamp up to 30 in. from the camera. The total weight of the camera unit (including camera, motor-drive, and lamphouse assembly) is approximately 4 Ib. The camera and lamphouse are shown in Fig. 8 which illustrates how a Wratten 88 A filter is held in place over the reflector by a grooved rubber ring that also serves to prevent any unfiltered light leaking around the edge of the filter. It will be noted that the camera also has an infrared filter (a Wratten 88) and that the flashtube is located so that the legs of the U are in a horizontal plane. This orientation tends to spread the light in the horizontal direction corresponding to the longer axis of the 16-mm frame. The power supply is a rectangular aluminum box with all components attached to the cover for easy servicing. The dynamotor is placed on top for maximum cooling.
In the laboratory the unit has operated very satisfactorily. Figure 9 is an infrared photograph of a test instrument bank taken with the recorder at 36 in., an angle of 30 deg, and an aperture of //1. 9. As data can be taken readily from exposures made at //2.8, it should be possible to photograph areas slightly larger than specified, and by the use of two recorders, more extensive instrument panels can be