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APPENDIX III 
CIRCUIT DIAGRAMS OF CAMERA TIMERS 
1. Timer for high speed camera L/ 
Timing of the film speed of the Eastman High Speed Camera Model III is accomplished 
by photographing periodic light flashes from a small neon bulb synchronized with an 
oscillator. The bulb is mounted close to the film on the inside of the camera. The 
timing marks appear along the edge of the film and are photographed simultaneously with 
the recording of the phenomena under observation. Operating at 3000 frames per second, 
the maximum speed of the camera, the circuit shown schematically in Fig. 139 produces 
one mark on the film every third frame. Under these conditions the distance between 
two adjacent marks can be measured to one tenth of one per cent (i.e. to one 4 sec) 
by the use of an optical comparator. 
The circuit was designed to operate from the output of a 1000 cycle per second 
tuning fork (General Radio Type 813A) although it can be used with other sinusoidal 
oscillators operating at different frequencies if slight changes are made in some of 
the circuit constants. The accuracy of the film speed determination depends on the 
accuracy of the oscillator frequency. 
The essential parts of the circuit are a clipper (tubes T5 and T3) which converts 
the input sine wave into a square wave; a counter circuit (Ts and Tg)” which divides 
the input frequency by two; a short duration pulse generator (T7 and Tg); a power output 
tube (Tg) to drive the neon flasher, and a tuning eye (Tj) to indicate the voltage of 
the sine wave from the oscillator. 
The neon bulb operates satisfactorily when cables as long as 1000 ft. are used 
between the timer and the bulb; this is the greatest length of cable which has been 
employed. The current in the neon bulb is adjusted by the potentiometer in the cathode 
circuit of To in order to control the intensity of the bulb; about 5 mamp is used at 
1000 cps and 3 mamp at 500 cps. 
This circuit can be used with an external power supply operating from a power 
line and delivering 300-500 volts at 40 mamp, in addition to current for tube heaters, 
or from a 6-volt storage battery if other power is not available. It is desirable to 
use a different source of power for operating the circuit than that used for operating 
the camera because, when the camera starts, a very large surge is introduced which 
may affect the operation of the electronic circuit, particularly if the power is 
obtained from a small generatcr, A Mallory Tyep VP-552 vibrapack and a filter section 
are built into the unit for opsration from a 6-volt battery and a Mallory Type 107 
battery charger is included for charging the storage battery from a power line. The 
1000 eps tuning fork, the vibrapack and the battery charger are included in a portable 
wooden carrying case which houses the electronic circuit. 
2. Timer for Jerome camera 
Inasmuch as the requirements for the Jerome camera were much less severe than 
those for the Eastman High Speed Camera because of the lower speed required, a simpler 
circuit shown in Fig. 140 was used to drive a neon lamp. A 50 cycle, single contact 
electrical tuning fork excites this unit. The signal from the fork is amplified 
and sharpened into short duration pulses in the first two stages and then applied to 
the grid of a Strobotron tube (SN4). The SN4 fires on each pulse, discharging the 
4 ft condenser through the transformer in its plate circuit. The output of this 
transformer drives a 1/4 watt neon bulb mounted in the camera and connected to the 
timer unit through a cable. The short discharge time of the 4 #f condenser insures 
short duration light pulses from the neon bulb suitable for dotting the filn. 
This is discussed in more detail by G. K. Fraenkel, Apparatus for the measurement of 
urst pressure means of piezoelectric es, NDRC No. A=-373, OSRD No. 6251, 
Chapter 9.3. 
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