Patent GB-657317-A (GB)
Title: Control system for adjusting a first voltage to equality with a second voltage
IPC: G01S13/78
Filed: 1948-06-29
Abstract: 657,317. Potentiometric voltage measurement. HAZELTINE CORPORATION. June 29, 1948, No. 17449. Convention date, July 11, 1947. [Class 37] [Also in Groups XXXVII and XL (c)] In a device of the kind described in Specification 655,187 for measuring a unidirectional potential, e.g. the range signal from a radar interogator-responder of the kind described in Specification 652,666, [Group XL (c)], by comparing it with a unidirectional potential derived from a motor-driven potentiometer which is automatically adjusted until the two potentials are equal, the energy content of the pulses operating the potentiometer motor is proportioned to the instantaneous difference between the two potentials to give rapid readjustment to equality with freedom from hunting. The unknown potential e2 and the adjustable potential e1 from the potentiometer are respectively fed through resistors 23, 23a . to the cathodes of diodes 31, 31a whose anodes are energized from a periodic potential generator 22 developing e.g. a sawtooth output whose amplitude range exceeds e1 and e2 and whose rate of variation is large compared with that of e2. Assuming e2 is greater than e1, the diodes are initially non-conducting and the generator saw-tooth voltage cyclically increases to exceed first e1 and then e2 so that the diodes successively conduct to develop sawtooth peaks across the resistors 23a and 23 which are initiated at times respectively representing the values of e1 an e2. The peaks are resistance capacity coupled to the grids of the tubes 32, 32a and successively overcome the normal cut-off bias to produce similarly timed negative-going square pulses which are directly anode coupled to the grids of the pentodes 37, 37a, whose anodes and screens are maintained positive with respect to the cathodes, through resistors 38, 38a, 39, 39a and whose suppressor grids are normally biassed negatively with respect to the cathodes through the resistors 40, 41, 40a, 41a. In each tube screen current normally flows, but not anode current, and the screens and suppressor grids are oppositely interconnected through condensers 42, 42a, so that on arrival of a grid pulse representing e1 the screen current of the pentode 37a is reduced and a similarly timed positive-going pulse is applied to the suppressor grid of 37, which, passes anode current until cut off by the arrival of a grid pulse representing e2. Thus a, negative-going pulse appears on the anode of 37 proportional in duration to e2-e1 and the positive-going pulse from the screen of 37 does not affect 37a since the latter is already cut off by the grid pulse representing e1 When their grid pulses are removed, 37 and 37a revert to their original conditions until the pulses recur on the next sawtooth cycle. The anode pulse of 37 renders the diode 43 conducting and charges the integrating load network 46 to a potential proportional to the pulse duration which dies, away exponentially giving an exponential' negative-going sawtooth waveform which is D.C. amplified by the triode 47 to a positive-going waveform and triggers the gas discharge tube 49, which is one of a pair 49, 49a, whose anodes are supplied in antiphase from an A.C. fed transformer 71 to energize one field 73 of a split-phase induction motor 27. The second field is energized from the A.C. supply through a quadrature condenser 76 and the tube 49 fires to deliver an energy pulse to the motor, which is mechanically coupled to vary the potentiometer 17. The motor is energized with successive pulses in correspondence with successive cycles of the sawtooth generator, and progressively readjusts the potentiometer to equalize e1 and e2. As e1 increases, the conduction of the diode 31a, and the initiation of the sawtooth pulse on the grid of 32a and of the negative-going pulse on the grid of 37a are correspondingly delayed, while the grid pulses of 32 and 37 are unaltered, so that a delayed positive-going pulse on the screen of 37 produces a shorter negative-going anode pulse. Thus the potential to which the load network 46 of the diode 43 is charged, and the magnitude of the energy pulse transmitted to the motor, is progressively reduced as e1 is adjusted towards equality with e2. A pointer 87 coupled to the potentiometer diode indicates the value of e2. If e1 is initially greater than e2 the device operates similarly, but the negative-going pulse representing e1-e2 is developed on the anode of 37a, charges the load 46a of the diode 43a and triggers the gas discharge tube 49a to pulse the motor in the opposite sense. The device operates similarly when e2 is variable, provided that the rate of variation is substantially less than the sawtooth periodicity. In a modification (Fig. 3, not shown), a D.C. motor is pulse energized through electronic switching tubes controlled by D.C. amplifiers fed from the integrating diode load networks.