464 - u - 



aDojt 2 milliseconds duration are repeated at intervals of 80 milliseconds - once for each 

 revolution of the drum. With autonatir, re-setting between impulses the unisalector ivcjl a operate 

 repeatedly with consequent damage. 



The control circuit must thus fulfil two conditions: (l) it must operate on a short 

 duration starting pulse and (2) it must then provide power to tht- uniselector for a long enough 

 period to make one step. After this the uniselector takes control. The power sufpl> musi, 

 however, be removed before the completion of the whole cycle in order to ivoid the initiation 

 of a further cycle. 



The first condition is achieved oy the rapid closure of the double wound Relay X 

 (Figure u). This relay is enerjised initially on a voltage of IIC volts through the contacts 

 X which are normally closed. This permits a surge of current to flow until operation of the 

 relay opens the contacts X . R-elay X is then maintained by the reduced current which flows 

 through the series resistor K . Under these conditions th3 operation of rel -ly X is sufficiently 

 rapid tc respond to the starting pulse (which is of duration 2 mill i spconds) . 



The relay Is also maintained by the operation of contacts X which connect the second 

 exciting coil of the relay to the negative end of the supply through the switch S (which is shown 

 closed in the position for '"hand rc-set") . 



The operation of the contacts X, completes the circuit to the driving magnet M of the 

 uniselector through the first wiper W and the single contact on which the wiper normally rests. 

 After the first step the wiper gains contacts with the 'homing" arc H. The driving current 

 through the magnet M -and the self drive contacts Dr Is then maintained until the uniselector has 

 completed a cycle of 25 steps. The wiper W then ccmes to rest again on the single contact 

 ment ioned above. 



By this time, the circuit to the positive end of the supply must e: broken if a second 

 cycle is to be avoided. This is brought about by the contacts Y . Relay V is operated by the 

 closure of the ccntacts X ■ It Is loaded with a capacitor C anj supplied through the resistor 

 R , and therefore closes relatively slowly. Consequently, current is supplied to the driving 

 magnet of the uniselector during the i.nterval between the operation of relays X and Y. This 

 interval is adjusted, by choice of tho values of R„ and C , and is just sufficiently long for 

 the wiper W, to gain contact with the "homing" are H. 



Operation of relay Y also causes the contacts Y, to open. The circuit may therefore be 

 rt— Sit by opening and closing the switch S. This de-energises relay X which In turn breaks the 

 supply to r-?lay Y. Relay Y Is then maintained for a short time by C,, so that the contacts X 

 open before Y, recloses and re— setting does not initiate another cycle. The contacts X also 

 operate a pilot 1 jmp which Is alight when relay X is not energised, i.e. when the circuit Is ready 

 for opi:rat ion. 



Autcmatic re-eetting is arranged by leaving the switch 3 open. Operation of relay Y causes 



the contacts Y, to open. Relay X is 'le-energi sed at this stage or when the starting contacts are 



opened if this should occur later. This in turn de-energises relay Y and leaves the circuit ready 

 for operation. 



Contacts 2 to 23 inclusive en the second tank of the uniselector are brought out to 

 socket to which the r( fleeter units ire plugged. Arrangements are made to fire the bulbs on 

 contacts 2 to 6, 2 to 12 or 2 to 23. 



Provision is made for testing the control unit and checkinj the speed of the uniselector 

 without firing the flash bulbs. K, and K are contacts on a non-locking test key. Closure of 

 Kj maintains the uniselector for as many cycles as are desired. Relay Z operates when K, is 

 closed and Is maintained via contacts Z, and the homing arc until the end of the cycle during 

 which Kj is opened. The contacts Z, break the circuit to the flash bulbs which consequently do 

 not fire during testing. The pilot lamp P is wired so as to light once per cycle as wiper No. u 

 passes over the last 1 contacts of the bank. 



The. speed of the uniselector Is controlled by means of the vairable resistor R.6. 



Result s 



