Patent GB-766251-A (GB)
Title: Improvements relating to apparatus for synchronizing electric signals
Inventor: JOHNSON KENNETH CHARLES
Filed: 1952-03-26
Abstract: 766,251. Automatic speed control systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 20, 1953 [March 26, 1952], No. 7711/52. Class 38 (4). [Also in Group XIX] In a digital electric computor in which data is transferable between a subsidiary magnetic storage drum MD and a main C.R.T. data store MS (see Group XIX) the drum is driven by a three-phase motor DM which tends to run faster than required and its speed is controlled by an electromagnetic brake BM in dependence upon the phase of slave pulses derived from a track ST on the drum with the leading edge of squarewave synchronizing pulses from the computing machine (as described in Proc. I.E.E., Part II, February, 1951, pages 29 ... 34). Further (i) a switch-valve is provided to make the squarewave asymmetric when the frequencies of the slave pulses and the square wave are unequal, whereby an output is obtained from the " phase " discriminator to correct the frequency error; (ii) a " coarse servo " valve is provided to over-ride the synchronizing system during starting before the drum has run up to speed, and prevent synchronizing in harmonic relationship at a low speed. Phase comparator.-In the computor a series of 24 " p " pulses are produced to each " beat " of the machine. A flip-flop circuit comprising a double triode V1, V2 is triggered by the 23rd pulse through diode D1 and normally reset by the 15th pulse to provide a square synchronizing wave which is clamped between the limits of 85 and 115 volts by diodes D6, D7. This square wave is applied to one grid of a double triode V4, V5, having the other grid held at 100 volts, whereby one or the other triode will tend to conduct. Conduction is blocked by a " tail valve " V6 in the absence of a slave pulse applied to line 102. When the system is synchronized the leading edge of the square wave will divide the sloping edge of the slave pulse and the valves V4, V5 will conduct for equal periods. If the slave pulse arrives slightly earlier or later, there will be unequal conduction periods, and the output is taken from transformer T and rectified by diodes D8, D9 to differentially charge capacitor C10, providing a resultant signal at terminal 120 to control the brake amplifier. Frequency discriminator (switch valve action). (i) Slow. The square wave has a normally longer positive portion whereby if the drum is running slow and there is a frequency difference between the pulses and the square wave, more pulses will occur during the positive period of the square wave, giving a resultant positive output from the discriminator to correct the frequency difference. (ii) Fast. If the pulses become phase advanced a negative potential is developed on C10, which biases V8 of a double-triode-switchvalve to cut-off, causing V7 to conduct, thereby lowering the cathode potential of D3 so that it passes " p-7 " pulses on line 108 to reset the flip-flop circuit VI, V2 earlier. This changes the asymmetry of the square synchronizing wave so that if the drum speeds up further causing a frequency difference, more slave pulses occur in the negative than in the positive part of the square wave, giving a resultant negative output from the " phase " discriminator to correct the deviation. Coarse servo action (during starting).-In the absence of an incoming signal coarse-servovalve V3 draws anode current in parallel with V1, thereby locking the flop-flop circuit so that it is not triggered and reset by the " p-pulses." Thus all slave pulses occur during a " positive " synchronizing input to the discriminator giving a resultant positive output to increase speed. When the speed is sufficient for there to be no possibility of harmonic synchronizing the output from the tail valve V3 on line 116 provides sufficient bias when rectified by D4 to block the coarse-servo-valve V3, and allow the flip-flop circuit to operate normally. Frequency control, as described above, then brings the drum to correct speed. Brake amplifier circuits, Fig. 6 (not shown).- The output signal from the discriminator at terminal 120 is fed to a shaping valve V9 in a negative feed-back loop introducing differential and integral components to prevent hunting, and thence to a pair of parallel connected output valves V10, V11, having the brake coils in their anode circuit.