Patent GB-910139-A (GB)
Title: Improved temperature control system
IPC: G05D23/24
Filed: 1958-12-08
Abstract: 910,139. Automatic control of temperature. DUNHAM-BUSH Ltd. Dec. 8, 1958 [Dec. 16, 1957], No. 39451/58. Class 38 (4). In an automatic temperature-control system the supply of heat to a space is controlled in dependence on a " minimum " signal indicative of whether the temperature is above or below a predetermined lower limit, a " maximum " signal indicative of whether the temperature is above or below a predetermined upper limit, and a " normal " signal indicative of whether the heat supplied is above or below that required by the ambient conditions, the signals being cyclically applied to a potential-responsive device to effect a heat control step in response to each individual signal, the " maximum " and " minimum " signals producing equal and opposite steps if the temperature is within said limits, the steps being in the same direction if the temperature is outside of the limits. As shown, a motorized steam valve 5, Fig. 1, supplying a convector 12 and a radiator 4, is adjusted by a signal from a control panel 13 responsive to variations in the resistances of a room thermostat 8, a window thermostat 10 and thermostats in the convector sensing the air temperature before and after heating. The control panel 13 comprises two low-resistance bridges interconnected by a high-resistance network to prevent unbalance in one bridge affecting the other. An amplifier, switched in sequence, senses the bridge voltages and controls the valve 5. The room thermostat 8, Fig. 3, has a temperature-sensitive resistor 46 connected in a bridge arrangement, an adjacent arm having compensating leads 52 and a resistor 162, the junction between the arms being formed by a room temperature-setting potentiometer 154. The other two arms of the bridge are formed by resistors 146, 152 and " maximum " and " minimum " temperature signals are derived from potentiometers 148, 150. A night temperature signal is derived from a potentiometer 156. The window thermostat 10 has a temperature-sensitive resistor 58 connected in an arm of a " normal " bridge arrangement, the adjacent arm being formed by a resistor 138 and compensating leads 60. The junction of the arms is formed by a balancing potentiometer 136. The remaining pair of arms are formed by temperature-sensitive resistors 74, 72 of the hot and cold air thermostats associated with the convector 12, which determine the rate of heat output to the space. The junction of the arms is formed by a heat-balance adjusting potentiometer 144 and the " normal " signal is derived from a potentiometer 140. The high-resistance interconnecting network 14 is fed through a rectifier 84 from a secondary 96 of a transformer 98. A manual gang switch 16 selects the mode of operation and a position 3 a time-switch 18 on a 24-hour cycle is energized, a switch 287 being closed for " night " operation, during which the " maximum " and " minimum " signals are disconnected ; a switch 285 is closed during " day " operation. A sequence timer 20, having a 60- second cycle, switches the signals derived from the bridges in sequence to an amplifier unit 22, via a capacitive voltage sampling network comprising resistors 348, 350 and capacitors 344, 346. The bridge signals are compared with the voltage from a follow-up potentiometer 28 sensing the extent of opening of the valve 5 under the action of a reversible motor 26. The amplifier unit 22 operates the appropriate relay 354, 356 to drive the motor 26 so as to restore the bridge to balance. The resultant movement of the valve 5 in a switching cycle is such as to maintain the desired room conditions. An electronic timer 24 is associated with the amplifier 22 and controls the time for which the capacitors 344, 346 are charged and the time for which the relays 354, 356 are actuated. The depression of an indicator button 406 reduces the cycling time of the timer 24 and a rapid indication of the condition of the system is obtained from indicator lamps 338, 340, 342, 372, 374. Specification 524,926 is referred to.