Patent GB-527349-A (GB)
Title: Improvements relating to electrical systems for controlling temperature
IPC: G05D23/24
Filed: 1939-04-06
Abstract: 527,349. Automatic control systems. MICRO SWITCH CORPORATION. April 6, 1939, No. 10835. Convention date, April 7, 1938. [Class 38 (iv)] Temperate.-A system for regulating the temperature of a space is arranged to depend upon the temperature to be controlled, and upon the rate of controlled transfer of heat; the latter is subjected to maximum and minimum limits the values of which depend upon the external temperature, a rebalancing device responding to each change in the adjustment of the heat-inputcontroller in order to arrest further adjustment in the same direction. The motor 1 which operates the steam valve of a heating plant, when energized at terminals 2 and 3 from the secondary of transformer 84 turns the valve towards the open position, and when energized at terminals ' 3 and 4 turns the valve towards the closed position. The motor is controlled by a galvanometer in dependence upon temperature measurements made by Wheatstone bridges consisting of arms containing a room-air thermometer 7, thermometers 8 and 9 placed above and below radiators to indicate the rate of heat input, window thermometers 10 and 11 subject to the external temperature, and various ordinary resistances and balancing potentiometers. With the master switch 21, and the cam-operated switches driven by motor 24, in the positions shown, the galvanometer coil 12 is connected between the tappings on the day setting potentiometer 31 and the potentiometer 40 which is mechanically coupled with the steam valve, and is shunted by the adjustable resistance 42. Movements of the steam valve, originated by unbalance in a bridge circuit, cause a rebalancing effect by means of the steam valve potentiometer 40 which tends to arrest further control in the same direction and thus to reduce hunting. Two other settings of the master switch connect the upper terminal of the galvanometer coil to the tapping on a night setting potentiometer 30, or a clock 51 which performs the necessary selection. Measurements of the rate of heating are made when the cam switches connect the upper galvanometer terminal to the bridge arms formed of radiator thermometers 8, 9, window thermometers 10, 11, and plain resistances and potentiometers 63, 64, 65, 66. 68, 69, 70. 71. The upper bridge is balanced at the upper limit of rate of heating, and the lower bridge at the lower limit. The effectiveness of the thermometers 10, 11 in determining the balance of the bridges is controlled by the gauged resistances 65, 66 and 70, 71. Each time the cam switches connect the galvanometer to a bridge, a cam 72 closes a switch 73, energizing a magnet 18 to draw down the depressor bar 14 on to the pointer 13. Thus when bridge circuits are unbalanced, either contact 19 or 20 is closed depending upon the direction of the unbalance. With the cams in the position shown, the measurement of the room air temperature by means of thermometer 7 is made, and operation of either contact 19 or 20 closes a circuit from transformer 84 to cause motor 1 to rotate the steam valve towards the closed or open position. When the cams have rotated through one-third of a revolution, the galvanometer is connected to the upper limit bridge. If the rate of heat transference is above the upper limit, contact 19 is closed, to operate relay 26, which locks up over contact 95 and winding 92, and also to energize the motor to move the steam valve towards the closed position. Contacts 90, being held open, prevent the steam valve from being further opened by closure of contacts 20 in response to a subsequent room temperature measurement. If the heat input is below the upper limit, contact 20 is closed and releases relay 26 by means of winding 96 if it has previously been locked up. When the cams have rotated two-thirds of a revolution the galvanometer is connected to the low limit rate of heat input bridge. If the rate of heat input is below the lower limit, contact 20 closes to cause motor to rotate the steam valve towards the open position, and also closes relay'27 which locks up and prevents the steam valve from being closed in response to another test. If the heat input is above the lower limit, contact 19 closes but cannot energize the motor ; it however releases relay 27 by means of winding 100 if it is locked up. Under normal conditions the control in dependence upon rate of heat input does not come into operation and the temperature is maintained under the control of the room air thermometer 7. If however a sudden change in the room temperature is producad, the radiator thermometers, which are more prompt to register a change in heat input, provide an over-riding control to limit the rate of heat transference and prevent hunting of the system. Lamps 101, 102, 103 indicate which test is in operation at any time. The master switch 21 has two positions in which the valve motor is energized, independently of any of the control apparatus, to open or close fully the steam valve. With the master switch in the " indicate temperature" position, the galvonometer is connected between a tapping on the bridge arm 109 and a tapping on the potentiometer 31. Potentiometer 31, which is calibrated, is adjusted until the galvanometer reads zero, and the position of the potentiometer then indicates the air temperature. With the master switch in the "indicate valve position" position, the galvanometer is connected between the tapping on potentiometer 115 and the tapping on the steam valve potentiometer 40, which is then shunted by the adjustable resistance. 117. The galvanometer deflection then indicates the valve opening. Specifications 505,796, 505,797 and 505,798 are referred to.