Patent GB-924790-A (GB)
Title: Improvements in or relating to cinematograph projection apparatus
Inventor: ROBINSON THOMAS
IPC: G03B21/50
Filed: 1958-02-10
Abstract: 924,790. Kinematograph projection apparatus. ESSOLDOMATIC Ltd. May 8, 1959 [Feb. 10, 1958], No. 4255/58. Class 97 (1). Film projection apparatus comprises two projectors, means for automatically changing over from one to other projector, monitoring means responsive to the operation conditions of said apparatus, and alarm means caused to operate by said monitoring means when predetermined operating conditions are departed from. A circuit diagram for one embodiment is given, only the operation of which is described here. The apparatus is connected to the mains when a switch 3 (to which a switch 22 is coupled) is closed, whereupon a relay A is energized to open a switch A1. Alarm and monitoring means.-During normal projection by the L.H. projector (not shown) a relay C is energized to close switches C1, C3 and open switch C2, a relay D is energized to close switches D1, D3, and a centrifugal switch 28, which rotates in contact with the film, opens. Coil 36 of a differential relay I is supplied through rectifying means 7 having a smoothing condenser 10 from a mains transformer 1, and coil 34 is supplied through rectifying means 33 having a smoothing condenser 35, from a transformer 32 monitoring the voltage across lefthand projector motor 31. Should voltage disappear from motor 31 due, for example, to a fuse 69 blowing, balance in relay I is upset. Switch I1 opens and relay A is de-energized causing a battery-energized alarm bell 20 to ring due to the closing of the switch A1. Thus, in the event of relay A being de-energized by mains failure, the alarm will also ring. A second differential relay K has a coil 38 connected in parallel with coil 36 of relay I and another coil 39 monitoring the voltage across the terminals of left-hand projector arc 40. In the event of undue voltage variations across the arc upsetting balance of relay K, switch K1 opens, relay A is de-energized, and alarm 20 is sounded as before. At the same time switch K2 opens and relay C is de-energized causing the appertaining dowser (not shown) to be closed. Also at the same time, switch K3 closes, thereby energizing the relay B, which opens switch B2 to shut off current supply to the projectors. If complete shut down is not required, link 60 may be removed, rendering switch K3 ineffective. Similar monitoring means indicated by double letters are provided for the righthand projector motor and arc, operating the alarm and shut down mechanism in the same way. In the event of film breakage or undue slowing down thereof, centrifugal switch 28 closes, relay B is energized, switch B2 opens to cause shut down and switch B3 closes to sound the alarm 20. A similar centrifugal switch 29 is provided for the right-hand projector. In the event of fire, the resistance of a thermistor 26 drops, relay B is activated by the increased current allowed to pass through it, and shut down and alarm are actuated as before. In the event of any component failing and undue current being drawn from the supply, relay CF is over-energized, switch CF1 closes and the alarm 20 sounds. Automatic change-over.-After the left-hand projector has been started by first pressing button 42 which activates relay D having associated switches D1-D4, D4 of which operates the motor and arc contactor M, and then pressing button 43 which activates dowser relay C having associated switches C1-C5, the relay F becomes energized after a delay due to thermistor 44, and moves switches F1-F4 to their alternative positions. Near the end of the film being shown, a series of three marks on the film are sensed by pick-off equipment comprising cold cathode valve CK, and pulses produced thereby actuate relay P having associated switches P1-P3, each of which becomes effective in turn. At the first pulse, switch P1 actuates relay H having associated switches H1-H4, H2 closing to operate a projector start warning buzzer 13, and H3 closing to charge a condenser 47. At the second pulse, switch P2 discharges condenser 47 through relay E having associated switches E1-E4, E1 closing to charge a condenser 49 and E4 starting the second projector. At the third pulse, switch P3 discharges condenser 49 through dowser relay CC having associated switches CC1-CC5, CC4 opening to de-energize relays D, C and F, and C5 discontinuing supply to relay H, thereby stopping the projector start warning. As relay D is de-energized, switch D4 opens to stop the first projector, and as relay F is de-energized, switches F1-F4 return to the positions shown, ready for a change-over from right to left. Tell-tale lights 14-17 indicate which projector is in use and whether automatic or manual control is in operation, the latter being in force when switches K1, I1, KK1, II1, of the alarm system are over-ridden by switches 24 and 25. In modifications, current monitoring of motors and arcs may be used instead of the voltage monitoring described. Specification 711,480 is referred to.