GB1085745A - Improvements in or relating to the measurement of heat exchange - Google Patents

Abstract

1,085,745. Measuring heat electrically; heat meters. SVENSK VARMEMATNING A. B. March 30, 1966 [March 31, 1965], No.14183/66. Headings G1D and G1N. An apparatus for measuring the heat lost in a loop of, for example, a central heating system, includes two thermistors 3, 4 Fig.1 in the inflow and return lines 1, 2 respectively, a switch 6 which closes each time a fixed quantity of heating medium has flowed through the loop, and a bridge circuit containing the thermistors 3, 4 which has its unbalance voltage, as indicated by a meter 18, nulled by a rebalancing potentiometer 16 driven by a motor 13 each time the flow measuring switch 6 operates, a counter 12 being driven by the motor so that its indication is proportional to both the temperature difference between thermistors 3, 4, and the rate of flow of medium. The rebalance potentiometer 16 is returned to zero after each operation by a spring 17. A transistor switching circuit 22 is arranged to energize the motor 13 and operate a clutch 15 when switch 6 operates, provided that the meter 18 is not reading zero, as detected by a photocell 19. In an alternative form, Fig.2 (not shown) a circuit (27) containing a capacitor (29) is charged from a D.C. source (25), each time the switch (6) operates, to null the bridge output voltage, the motor (13) being arranged in this case to drive only the counter 12 for a period determined by the time constant of the circuit, and by the temperature difference. The rebalancing operation, having been initiated by switch 6, is allowed to continue by a self-holding relay 23 which releases when rebalance is achieved, as detected by the photo-cell 19. The temperature differential may be measured alternatively by Bourdon tubes (30, 31) Fig. 3 (not shown) responsive to the pressures in capillaries (36, 37) connected to liquid filled capsules (3, 4) in the inflow and return loops, the Bourdon tubes being connected to a differential gear (38), the output shaft (39) of which is connected to a disc (32) having an arcuate window (33). A second disc (35) also with an arcuate window (34) is connected to the counter motor (13) via a clutch (15), and is rotated through the same angle as the disc (32) has been turned through each time the switch (6) operates, the clutch being deenergized when a light source (20) first ceases to be detected by a photo-cell 19. A spring (17) returns the second disc (35) to its original position after each operation.