Patent GB-650740-A (GB)
Title: Improvements in control or/and measuring apparatus
IPC: G01K7/02
Filed: 1947-10-10
Abstract: 650,740. Automatic temperature control systems. BAILEY METERS & CONTROLS, Ltd. Oct. 10, 1947, No. 27236. Convention date, Oct. 14, 1946. [Class 38 (iv)] [Also in Groups XXXVI and XXXVIII] Apparatus for controlling and/or measuring the magnitude of a variable wherein a continuous control potential is fed to a reactor converter, the output of which operates a device for effecting the control and/or measurement, includes an anti-hunting circuit adapted to provide a current flow of invariable direction and including a capacitative or inductive coupling, and which is adapted to provide a continuous voltage derived from the flow of current of invariable direction varying with the rate of operation of the device in such a manner as to be larger the greater the rate of operation and opposed in its action to that of the control potential. As applied to the temperature control of a furnace 1 (Fig. 1) a thermocouple 4 in heat transfer relation with the furnace is connected in a standard potentiometer circuit including a balancing resistance 5, any D.C. output from the circuit being fed to an A.C. bridge 19, comprising two reactor converters A<SP>1</SP>, B<SP>1</SP> of the type described in U.S.A. Specification 2,447,338, the output of which is of a magnitude and phase sense corresponding to the magnitude and polarity of the D.C. input which in turn depends upon the magnitude and sense of the temperature deviation in the furnace from a predetermined normal value. The output from the A.C. bridge is fed via an amplifier 30 to a phase-sensitive motor control 32 which operates a motor 28 in a sense tending to restore the temperature of the furnace to normal by operation of a fuel valve 3, the rate of rotation of the motor being dependent on the magnitude of the D.C. input to the bridge 19. The motor also operates an indicator 55 on a scale 56, and adjusts the balancing resistance 5 so as to rebalance the potentiometer circuit and also operates the sliding contact 64 of a resistance 63 in a circuit 60 which produces across a resistance 61 a voltage which is proportional to the speed of the motor 28 and opposes the flow of current from the potentiometer circuit, thus preventing hunting. Operation of the motor 28 causes contact 64 to move along the resistance 63 and produce a flow of current of invariable direction through a rectifier 65 and resistance R1. While the current flow through R1 varies, a condenser 69 passes current through the effective part R of the resistance 61, but as soon as the flow through the resistance R1 becomes constant, no current passes the condenser 69, and it may be shown that the voltage across R=iR#C#RdE 1 /dt#C#RK 1 EacdK/dt, where K 1  is a constant, K represents the position of the contact 64 along the resistance 63, and Cf is the capacity of condenser 69. Thus the voltage across R is nearly proportional to the rate of change of position of the contactor 64 and therefore to the speed of the motor 28. The circuit 60 is shown as fed from an A.C. source via a transformer 62. In modifications (Fig. 2, not shown), the circuit 60 is fed from a D.C. source, the rectifier and transformer then being omitted. In further modifications (Fig. 3, shown, and Figs. 4 and 5, not shown) the output across the resistance 61 is made to depend upon the rate at which an adjustable core 93 of a transformer 82 feeding the circuit is moved by the motor 28.