GB565215A - Improvements in or relating to the electrical measuring of temperature - Google Patents

Abstract

565,215. Automatic control. STEGHART, F. L. Jan. 29, 1943, No. 1549. [Class 38 (iv)] [Also in Groups VI, XXXVIII and XL] In a system in which it is undesirable to mount a resistance-thermometer at the place of which the temperature is to be measured, it is mounted at a convenient spot which normally has the same temperature, and its effect is assisted or opposed for a period, when the temperature changes, by that of a thermo-battery with its junctions situated respectively at the place of which the temperature is to be measured and adjacent the resistancethermometer. As shown in Fig. 1, milk being pasteurized flows along a pipe 1 containing one set of junctions of a thermo-battery, the other set of junctions and a resistance thermometer which forms one arm of a Wheatstone bridge being thermally associated with the exterior of the pipe by means of a mass 61 of conducting material surrounded by a glasswool &c. 13. In normal conditions, both sets of junctions are at the same temperature and the condition of an indicating relay 24 is governed entirely by the extent of unbalance of the bridge, the output of which is applied to a galvanometer 17 which reflects more or less light on a photoelectric cell 20 forming part of a potential divider, the other half of which is constituted by a condenser 21 and the output of which is applied to a gas-filled thermionic tube 22 arranged similarly to that described in Specification 537,784, [Group XL]. The anode current of this tube which controls the indicating relay 24, flows in a resistance 18 in the galvanometer circuit to produce a voltage drop which tends to return the galvanometer to zero. When the temperature exceeds a given value, the relay 24 lights a lamp. When the temperature falls below another value, relay 24 energizes a relay 29 which locks up and operates a valve 28 to divert the milk in readiness for its repasteurization. When the temperature of the milk changes, the output of the bridge is assisted or opposed by that of the thermobattery so that the indicator relay responds immediately to the change in temperature. Relays 16, 15 respectively cause the substitution of a standard cell for the combined thermometer voltage and the shunting of the thermobattery. In a modification. Fig. 2 (not shown), one set of junctions is in the milk pipe and the other set and the resistance thermometer are thermally associated with a pipe carrying the heating water. This arrangement also includes a device for delaying the restoration of the milk-diverting valve for a period. A thermostat causes the shunting of the thermometer outputs if the milk temperature falls to an abnormal extent to avoid damage to the galvanometer 17. The system may control the temperature of the hot water as described in Specification 542,962.