Patent GB-880005-A (GB)
Title: Photo electronic triggering device
IPC: B64F1/02
Filed: 1957-10-11
Abstract: 880,005. Digital electric calculating-apparatus. KOLLSMAN INSTRUMENT CORPORATION. Oct. 11, 1957 [Oct. 15, 1956], No. 31840/57. Class 106 (1). [Also in Group XL (b)] In a system for triggering the release mechanism of a " pop up " barrier cable 25, Fig. 8, controlling the landing of aircraft on the deck of a carrier, the optimum triggering time is determined by a computer arrangement which is operated in response to two signal pulses generated as an aircraft passes through two beams of light 20, 21 projected across the deck in the approach to the barrier cable (see Group XL (b)). Means are also provided for preventing the rise of the cable when the aircraft speed is outside a predetermined range. From Fig. 8 it may be determined that the optimum time delay, between the passage of the aircraft through light beam 21 and release of the barrier cable, where D 1 , D 2  and D 3  are the distances shown, #t is the time between signal pulses, which is inversely proportional to the aircraft's speed, and r is the time delay between initiation of the barrier cable triggering pulse and its release. The computer includes a binary counter arrangement and a diagram of its operation is shown in Fig. 9, in which T 1 C and T 2 C are the times of receipt of the two signal pulses and time TTC is the time of triggering the barrier release mechanism. At time T 1  the counter commences to count at rate m 1  from a preset figure n<SP>1</SP>, when it reaches its full count n it reverts to zero and carries on counting. At time T 2  the counter is triggered to its complement state and carries on counting at a new rate m 2 . When its full count n is reached the return of the counter to its zero state produces a signal which triggers the release mechanism. From the geometry of Fig. 9 it can be established that the equation for the time interval and that this equation is of the same form as that given above for TO. The computer includes two ten-stage binary counters 117, 118, Fig. 11, operating in parallel and a gate circuit 120 which ensures agreement in the output signals of the counters before these signals are passed to the following circuitry. The two signalling pulses produced in deck units 22, 23 in response to the passage of an aircraft through the beams are applied via common amplifying circuits 30, 31, selective circuit 99, detector 108 and differentiating circuit 110 to trigger a monostable flipflop circuit 111, which produces a pulse of length equal to the time taken for an aircraft flying at the upper limit of the predetermined range to pass between the two beams. The output signal of the flip-flop is differentiated and triggers a bi-stable flip-flop 113 which controls in-count gate 115. Counting pulses at frequency fo are applied to counters 117, 118 which commence counting at rate m 1  from a preset figure n<SP>1</SP>. When the counters reach their maximum count they revert to zero and produce an output pulse which is prevented from triggering the barrier release at agreement gate 142 which requires the presence of a coincident signal from bi-stable flip-flop 114 before passing a triggering signal. The counting proceeds until the arrival of the second pulse which triggers flip-flop 113 back to its initial state. This change of state produces a signal which is differentiated in unit 132 and triggers bi-stable flip-flop 114 controlling out-count gate 116. Counting signals are applied via this gate and two divider stages to the counters which now count at new rate m 2 , in addition the counters are complemented by a signal supplied from out-count gate 116. When full count is reached an output signal is produced which is passed to agreement gate 142 and at the same time the counters and flip-flop 114 are reset to their initial states. The resetting of flip-flop 114 produces a signal which is differentiated in unit 141 and applied to gate 142. The gate then passes a triggering signal to thyratron 26 which fires and operates the barrier release. When an aircraft flying at a speed above the upper predetermined limit passes through the beams, the second pulse arrives at flip-flop circuit 111 before the completion of the pulse generated as a result of its initial triggering, only one pulse is therefore applied to bi-stable flip-flop 113. The counters then count up to their half count n/2 and produce an output signal which reverts flip-flop 113 and the counters to their initial state. When an aircraft passes through the beams at a speed below the limit, the counters reach their half count before the arrival of the second complementing signal and the counters are reverted to their initial states.