Patent GB-1232603-A (GB)
IPC: G05D3/14
Filed: 1968-09-30
Abstract: 1,232,603. Measuring pressure electrically. WALLACE & TIERNAN Inc. Sept.30, 1968 [Oct.2, 1967], No.46329/68. Headings G1N and G1U. [Also in Division H2] A control system for a reversible motor M comprises a conductance control device connected between an A C. source 12, 10, 93 and the motor M and operable to cause energization of the motor during any half cycle of the source and to maintain that energization only until the end of that half cycle. A controller 39 produces an A.C. control potential the phase of which, with respect to the source determines the direction of rotation of the motor and the amplitude of which determines the extent of the motor energization. A gating device, e.g. a uni-junction transistor 81 renders the conductance control device conductive when a capacitor 74 is charged to a predetermined positive potential by a signal from the controller 39. The charging of the capacitor 74 is controlled by a discharge limiting potential which varies at twice the source frequency, is negative at the beginning of each half cycle of the source, but otherwise has substantially the positive half of a sinusoidal waveform throughout each half cycle of the source. This discharge limiting potential which may be derived from rectifiers 14, 15, 28, 29 and resistors 33...35 is applied to a diode 76 to permit the diode to conduct and discharge the capacitor 74 at the beginning of each half cycle and thereafter limits the charge of the capacitor to an instaneous value not exceeding that of the discharge limiting potential. A negative feedback circuit 97...104 is connected between the motor energizing circuit and the circuit which supplies the signal from the controller 39. This last circuit may be an amplifying circuit having transistors 45, 53 and 69. The circuit constants are such that in the absence of an A C. control signal from the controller 39, the motor M is energized by substantially equal and alternately opposite short pulses and does not rotate. When the A.C. control signal is present, it is effective to cause the conductance control device to conduct only on one set of alternate half cycles of the A.C. supply source, so causing the motor to rotate in the direction determined by the phase of the control potential. The conductance control device may comprise controlled rectifiers 89, 91 and diodes 92, 94 as shown, or a triac, Fig.4 (not shown). The controller 39 may be a differential transformer in which a measuring device, e.g. a pressure sensitive capsule 37, moves a secondary winding with respect to oppositely polarized primary windings 40, 41.. In this case the motor M drives a counter 96 and displaces the windings 40, 41 to restore balance in the transformer. Fig.4 (not shown) illustrates the use of the system to measure a direct current or direct voltage signal, the controller comprising a Wheatstone bridge, energized by alternating current and having a fieldeffect transistor in one limb. The direct signal acts through a potentiometer to control the resistance of the transistor and the motor operates the slides of the potentiometer. In a further arrangement, Fig. 3 (not shown) the system is used to control a chlorinator valve, the controller being an A.C. bridge circuit with two variable resistors, one being adjusted by a water flowmeter and the other by the motor as it operates the chlorine valve.