Patent GB-906124-A (GB)
Title: Improvements in controllers
Inventor: STEGHART FRITZ LUDWIG FELIX
IPC: G05B11/01
Filed: 1957-11-22
Abstract: 906,124. Automatic temperature control systems. RHEOSTATIC CO. Ltd. Oct. 30, 1958 [Nov. 22, 1957; Jan. 15, 1958], Nos. 36465/57 and 1496/58. Class 38 (4). A control system for controlling a physical variable-such as the temperature in a space to be heated or cooled-comprises a controller responsive to the variable and effective to control the operation of a number of correcting units, the control being transferred from one correcting unit to another by means of transfer switches operated by the correcting units, the control effected by the controller having a proportional and an integral function. A space to be heated, cooled or ventilated includes heating means controlled by a reversible motor Ml, dampers on the fresh air and recirculated air intakes operated by a similar motor M2, cooling means operated by another similar motor M4 and lastly yet another reversible motor M3 which provides a " dead zone " in the control by causing the set temperature of the space to be increased between the operation of motors M2 and M4. The temperature of the space is sensed by a resistance thermometer 4 which, by way of a valve 8, controls the proportional potential appearing across a potentiometer 15 which then controls, by way of further valves 16, 17, the current passing through relay coils RC, RH. These relays are set to operate at differing current levels so controlling the potentials appearing on terminals A, B or A, C and thereby determining the direction of rotation of the motors M1-M4. A feedback supply is obtained from a rectifier 34 which is fed, by way of terminals DH to potentiometers 40-43 having slides driven by the respective motors M1-M4. The feedback from these potentiometers by way of terminals E, F, G controls an integrating circuit 24, 35 whereby motors M1, M2, M4 are constrained to move in a stepwise manner, whilst the feedback from potentiometer 42 by way of terminal J is taken to a resistor 11 and thus affects the proportional signal taken from potentiometer 15. If the space being controlled is overheated the sensing thermometer 4 will cause operation of relays RC, RH such that motor M1 runs to close the heating valve and drive the slider of potentiometer 40 downwardly. If when the heating valve is closed the space is still overheated, the limit switch LS1b closes to transfer the control to motor M2 which runs to close the dampers for the recirculating air and open those for the fresh air. Should this not effect sufficient control, limit switch LS2b closes to transfer the control to motor M3 which runs to alter the potential on the potentiometer 15 and thus increase the set temperature of the space. Should even further control be needed the limit switch LS3b closes to transfer the control to motor M4 which runs to open the cooling valve to decrease the temperature of the controlled space. Similar control is exerted when the controlled space is underheated with the motors M1-M4 operating in the reverse fashion. A further embodiment is described wherein one motor is arranged to effect the controls exerted by motors M2, M3 of Fig. 2 and in which two thermostats are placed in the fresh air intake, these thermostats having different control ranges. Specification 906,125 is referred to.