GB1261917A - Improvements in or relating to systems for synchronising a film transport and a magnetic tape replay machine or other signal reference source - Google Patents

Abstract

1,261,917. Automatic speed control. H. D. FORD [trading as H. F. ENGj. March 28, 1969 [April 1, 1968; July 10, 1968), Nos. 15571/68 and 32940/68. Heading G3R. The relative phase of pulses derived respectively from a generator 1 driven by a film projector and a reference source which may be a magnetic tape recorder is compared and used to control the supply of current to the projector motor so as to maintain synchronizm between the two sets of pulses. A lamp 3 and a perforated wheel 2 driven by the projector produces a square signal from a photo-electric cell 4. This signal is differentiated and used to trigger a monostable multi-vibrator 7. A sawtooth waveform is taken from the monostable and applied to a gate 8. Pulses from the tape 9 or, in the absence of the latter, from the mains supply, are differentiated at 14 and trigger a second monostable 15 having a much shorter time constant. Narrow pulses taken from the monostable 15 open the gate 8. Upon the relative phase of the pulses depends the amplitude of the sawtooth when the gate 8 is open. The output of the gate, which thus raises in amplitude with the relative phase, is integrated and controls the time constant of a monostable 17 triggered by pulses from the mains supply. The output of the monostable 17 is differentiated and the positive going pulses used to control the firing point of a thyristor 21 supplying the motor. The use of different wheels 2 for different systems is discussed, the required number of holes for several standard systems being given. The wheel 2 may be replaced by a magnetic wheel or tachogenerator.