Patent GB-501800-A (GB)
Title: Improvements in or relating to temperature control systems and temperature responsive apparatus
IPC: G05D23/19
Filed: 1937-08-24
Abstract: 501,800. Automatic control systems. MINNEAPOLIS-HONEYWELL REGULATOR CO. Aug. 24, 1937, No. 23216. Convention date, Nov. 4, 1936. [Class 38 (iv)] Temperature is controlled by means responsive to a change in the rate of sound transmission in a medium subject to the temperature. Three methods are described. The average temperature of fluid in a long pipe 10, Fig. 1, is adjusted by varying resistance 19 in series with heating means 13 in accordance movements of a two-phase motor, one winding 34 of which is energized by A.C. with a definite phase relation to the A.C. energizing a telephone receiver 25 in the pipe. The other winding 33 is energized by the A.C. generated in a second receiver 30. When the temperature in the fluid is correct, the phase shifting circuit 43, 41 is adjusted at 44 to hold the motor stationary. The motor moves to adjust the resistance 19 and also the phase shifting resistance 43 in a sense determined by any temperature change owing to change in timing of the sound waves reaching 30. The temperature of a bath 50, Fig. 2, is controlled by adjusting a gas valve 54 by reversed motors 64 selectively energized by a relay 116 in accordance with the change in phase between the output of a high-frequency oscillator 59 energizing a telephone receiver 57 and the output of a telephone receiver 77 actuated by the sound transmitted through a pipe 56 in the bath. The currents in the plate circuits of a double triode 82 are balanced under correct temperature conditions but, resulting from a change in temperature, a change in the phase of the potentials of the grids, which are energized through an amplifier 78, causes unbalance and selective operation of relay 116 which has two coils each in one plate circuit. The motors adjust a condenser 63 to change the frequency of the oscillator 59 and restore balance at the same time as the gas valve. An indicator 75 may be included. The temperature of a room 155, Fig. 3, is controlled by starting and stopping the blower motor 152 of an oilfired boiler of a heating plant in accordance with the relative change in the rate of sound transmission in two pipes 156, 157 arranged around the room and filled with different fluids, such as ethyl ether and ethyl alcohol, having a considerable differential change in sound transmission rate with temperature. An adjustable U-tube 158 determines the desired temperature. A constantly running motor 175 operates cam-switches 169, 190 to close intermittently circuits respectively discharging a condenser 171 and energizing two gas-filled tubes 196, 197 with D.C. The condenser discharge produces a sound impulse in a telephone receiver 165 which is transmitted through both tubes and received simultaneously in receivers 194, 195, each terminating one tube, so long as the temperature is correct. When a change occurs the simultaneous energization of the grids of the tubes 196, 197 is disturbed and one becomes energized first, whereupon the other tube is prevented from discharging by reason of the drop in its plate potential produced by a resistance 224. The coils of a relay 229, each in series with a tube, are thus selectively energized to close the circuit of the blower motor 152 when the temperature is low and to open it upon a very small rise from the normal.