GB998534A - Thermally sensitive capacitive circuit element - Google Patents

Abstract

998, 534. Measuring temperature electrically. INTRON INTERNATIONAL Inc. March 20, 1962 [March 27, 1961], No. 10599/62. Heading G1N. [Also in Divisions G3 and H1] A positive temperature coefficient capacitor with a polyvinyl fluoride dielectric is used in measuring temperature and controlling in accordance with changes in temperature. Its response rate is determined by mounting it in a housing of predetermined heat capacity or in association with a slug of high heat capacity e.g. of lead. In a circuit providing remote indications of temperature the frequency of a Hartley oscillator is determined by such a capacitor in its resonant circuit. The variable frequency signal is transmitted to a remote station where it is converted to a visual indication. Alternatively, the transmitter comprises a two stage transistor-oscillator (Fig. 12) including a Wien bridge including temperature sensitive capacitors 1300<SP>1</SP> and 1300<SP>11</SP> in parallel arms with ganged frequencyselector resistors 1335<SP>1</SP>, 1335<SP>11</SP> and amplitude controlling rheostat 1380. In another system for setting off an alarm or e.g. throttling a fuel supply in response to an abnormal temperature condition at a remote station a control signal of variable frequency is transmitted to a parallel resonant circuit including the temperature sensitive capacitor at the station. The threshold temperature at which a relay connected across the circuit is tripped is thus determined by the frequency of the control signal. In another arrangement the capacitor is used (Fig. 6) to switch off electric motor 720 if it overheats. The output of bridge 733 is fed via transistor amplifier 737 to a phase comparator 740 the output of which operates relay 732 when the motor temperature exceeds a preset level. In an alarm system (Fig. 8 not shown), the capacitor forms part of a series resonant circuit controlling the firing point of a controlled rectifier in the alarm circuit while in another arrangement (Fig.9,not shown),for switching off the electroplating current when the electrolyte temperature falls too low it is in a parallel resonant circuit controlling the voltage across a relay.