526 _ 2 . 



Mu ltt flashing Equipment . 



The electrical equipment for producing the light flashes in the Arditron lamp is housed in the 

 laboratory for reasons of bull* and general convenience of servicing. This has necessitated the use 

 of a transmission line 80 feet long to connect the equipment to the lamp. it has been necessary to 

 devise an electrical circuit which would minimise the undesirable effects on the efficient operation of 

 the Arditron due to the total inductance of the transmission line. The circuit adopted is shown in 

 Figure 2 and its operation is as follows:- 



The reservoir condenser, which serves as the power supply, consists of 28 2-fflicrofarad condensers 

 connected in parallel and trickle charged to 8,000 vclts by a neorv-sign transformer and ten H176 

 westlnghouse rectifiers in series. 



A seven-inch diameter Tufnol disc, rotating at 3,000 r.p.m., carries 20 short lengths of n b.a, 

 brass studding screwed through the disc at equally spaced intervals round a circle concentric with the 

 axis of rotation. The disc is mounted so that these lengths cf studding pass in succession between 

 two pairs cf fixed points, S. and S. the clearance being abjut 6/1,000 inch. Thus every millisecond 

 cne of the twenty studs passes between the points S, and s,. These fixed p.:ints are so arranged that 

 there is half a millisecond interval between studs passing between them, i.e. if a stud is in line with 

 S, at a certain instant then half a millisecond later a stud will pass s. and vice versa. 



with the relay R closed, when one of the studs passes between the points S,. 'be gaps at s 

 break down and the intermediate condenser, capacity o.5 microfarad, is charged up to the voltage of the 

 reservoir. The S-ohm resistance limits the current in this charging stroke. 



Half a millisecond later, when there is no conducting path at s,. a stud passes between the 

 points S,. This gap breaks down and the intermediate condenser discharges dowr> the concentric cable 

 thus charging up the final condenser, capacity 0.2 microfarad. After a time of the order of 10 to 12 

 microseconds, when the final condenser is nearly fully charged, the voltage applied to the grid of the 

 Arditron reaches its breakdown voltage and triggers the tube which breaks down and a discharge passes 

 between anode and cathode. 



The main requirement of the lamp is that it should produce a high intensity light flash of short 

 duration, and it is therefore necessary that the current pulse in the lamp should be of great intensity 

 and short duration. The final condenser is therefore housed in the lamp housing as close to the Arditron 

 as possible, thus keeping the inductance and resistance of the discharge circuit as low as possible. 

 It is estimated that the peak current in this discharge is from 3,000 to 5,000 anperes, and the pulse lasts 

 for about a microsecond. This is followed by ? much longer discharge due to the intermediate condenser 

 discharging down the cable and the lamp. The 30-ohm. resistance, however, limits the current in this 

 part of the discharge to a meximum value of 200 ?.mpercs, which decreases with a time constant of the 

 order of 15 microseconds. Thus the pulse of current in the lamp is conjectured to be somewhat as in 

 Figure 3. 



By suitable adjustment of the lens aperture and the speed of thp film it is possible to arrange 

 that the intensity of light falling on the moving film due to the long "tail" of the current-t ime curve 

 shall be less than the threshold value for the film, so that only the short peak of the light pulse 

 registers photographically. However, in high lights, where the level of the illumination is locally 

 very much higher than that over most of the picture, it is impossible to prevent some of this later 

 portion of the discharge registering photographically. This causes a short "trial" of light, extending 

 in the direction of motion of the film, on each of the high lights. Th«j pictures obtained by this 

 circuit are nevertheless much sharper than those obtained by discharging a condenser of the same capacity 

 as the final condenser down the 80 feet of cab'le with the lamp at its far end. 



The rotary spark gap isolates the lamp from the intermediate and reservoir condensers during 

 the recharging stroke. This two-stage process is repeated every millisecjnd until the relay R is 

 cpened cr until the voltage cf the reservoir fells below a critical value. In normal operation twc 

 groups of flashes are produced, each consisting cf 20 t: 25 flashes, and these groups must be timed 

 relative to the firing of the explosion with an accuracy cf three or four milliseconds, so that the 

 relay R must" operate quickly and repeatedly. To this end a Post office high speed relay has been 



adapted 



