_ 3 - 463 



Time marking is provided By meins of ci crater tuoe operating in parallel with the tude 

 in the Fastax camera. The two records are synchronized by interrupting the timing traces for 

 0.2 milliseconds apout 16 milliseconds .ifter firing the charge. 



In order to facilitate comparison cf pressure records, the drum camera speed is adjusted 

 to 750 r.p.n. before th> Fastax c;-mora is start. ^d, the spied being checked as follows:- 

 a radial line painted upon the driving pulley of the drum is illuminated by means of a neon 

 stroboscope operating at a tuning fork controlled frequency of fifty flashes per second. When 

 the drum is running it 75C r.p.m. the line is seen as a cross. The charge is fired when the 

 cross appears stition.iry. 



Sequ';nce timing . 



Sequence uf events. 



The technique of timing the photographic and pressure records is influenced by features 

 of the design of the oscillograph recording camera which will first be described with the aid of 

 Figure 2, The film is wrapped around a drum 7 feet in circumference, the ends of the film being 

 threaded through a slot in the periphery of the drum and held in place by means of a wedge. 

 Exposure of the film during one revolution of the drum is regulated by the shutter S (Figure 2). 

 The shutter consists of a brass pi ite, constr^.inod to fill vertically, a slot in the plate 

 permitting .jxpooure of the film as the r.hutter passes the gate in the body of the camera. 



The shutter is released by the electromagnetic trigger T at such a time that exposure of 

 the film begins a few inches after the join in the film has passed the gate. Timing is effected 

 by means of the contactor C mounted on the spindle of the cam':ra drum, the angular position of 

 the contactor segment being -'.djust ible with respect to the position of thi^ join in the film. 



Th whole sequence will now be made clear by Figures 2 and 3, The drum camera is first 

 run up to "peed. When the speed is stCidy it 750 r.p.m, the F.istax cvnora is started; thereafter 

 timing is regulated by two circuits. The first, a simple d'lay circuit, governs the time of 

 firing the ch^irge relative to the start of the Fastix Crimera. Contacts arc closed at i 

 predetermined time after the start of tho camera, (This circuit is not required in cameras such 

 as the Eastman High-speed camera, which incorporates a mechinical switching device). 



This closure ccmpletes the circuit to the contactor C, Wh- n the contactor segment reaches 

 the brush, the second control circuit is sot in operation, (X'tails of this circuit, which is 

 built around ; Post Office uniselector, ere given telow. On receipt of the signal from the 

 contactor, relays are opcntod which -llow the uniscl jctor to perform one cycle. 



The cycle is perfQrmcd in twenty-five steps at intervals of 16 milliseconds. The flash 

 bulbs are fired on step number 2 and on subsequent steps, (The number of steps used depends upon 

 the length of record required), 



A signal is supplied to the circuit which operates the drim camera shutter on step number 1, 

 The charge is fired on step number u, on step nunber 5 a Synchronization pulse is injected into 

 the time marker supply. 



Control ci rcuit . 



This circuit is designed (1) to time the opening of the shutter in the drum camera used in 

 pressure recording, (2) to provide a synchronization pulse to the time markers on the Fastax and 

 and drum cameras. (3) to fire a sequence of photoflash bulbs and (u) to fire the charge. These 

 operations are performed by a Post office uniselector (Type U2A) , The remainder of the circuit 

 starts the uniselector at the apprepriaf; time, ensures that it performs one cycle only, and permits 

 the testing of the unisiloctor without firing th^ flash bulbs. 



The circuit is shown in Figure U; it is operated by connecting the terminal marked "start" 

 to the negative side of the 110 volt supply. The duration of this contact may be either prolonged 

 or as Short as a Ton milliseconds. in either case, the uniselector performs one cycle and then 

 stops. If the switch S is in the open position, the circuit re-sets itself automatically when 

 the starting contact is removed. When the switch S is closed, the circuit must be re-set by hand 

 before another cycle is performed. 



This feature (hand re-set) is necessitated by the nature of the contact which operates the 

 circuit in practice. As has been mentioned this circuit is started by the rotary contactor on 

 the drum camera. Consequently, once the circuit to this contactor has been made, impulses of 



