GB991006A - Improvements in or relating to the measurement of heat - Google Patents

Abstract

991,006. Measuring heat flow electrically. SATCHWELL CONTROLS Ltd. Dec. 14, 1962 [Dec. 21, 1961], No. 45918/61. Heading G1N. The heat supplied to a heating system is determined by measuring the quantity of electrical energy supplied to a heater 4 (Fig. 2), located in a measuring conduit 5 which passes a pre-determined fraction of the fluid in the system return conduit, to maintain the temperature of the fluid in the measuring conduit, as measured by a resistance thermometer 9, equal to the temperature of the fluid at the inlet to the flow conduit, as measured by a resistance thermometer 1. The resistances 1, 9 are combined in a bridge circuit feeding an amplifier 13 which energizes a relay 13a whose normally open contact 17 controls the energy supplied to the heater 14 through a voltage stabilizer 19 and is parallel with a synchronous motor and counter 18. In an alternative arrangement (Fig. 2), two pairs of resistance thermometers 1, la and 9, 9a respectively located in the flow and return conduits, and downstream and upstream of the heater 14, are combined in two bridges A, B, the outputs being fed in opposition to amplifier 13. The bridge voltages are unequal to ensure that the unbalance signals are equal when the heat supplied to heater 14 is the appropriate fraction of the heat lost in the heating system 3. To improve accuracy, the voltage supplied to bridge A is reduced as the temperature in the return conduit 4 rises, by a thermister 12c located in conduit 4 and connected in parallel with the bridge input.