Refrigeration systems

摘要

1,070,847. Automatic temperature control systems. CARRIER CORPORATION. Aug. 5, 1964 [Sept. 25, 1963 (2)], No.31859/64. Heading G3R. In a fluid moderating system, such as a refrigerating apparatus, the temperature of fluid entering and leaving the system is measured so that one temperature measurement modifies the other. A sensor 45 comprises a negative temperature coefficient resistor 36 in intimate thermal relationship and a positive coefficient thermistor 37 in less intimate relationship with the leaving fluid, which resistors form with resistors 39-43 and centre tapped transformer 31-34 an A.C. bridge, the output of which is modified by a negative coefficient resistor 61 in the fluid entering line. The angular displacement of the bridge output via potentiometer 39 from lines 33, 34 fires one of the thyristors 75, 78 which fire through transformers 80 or 100, further thyristors 93 or 111 which load shading windings 96 or 97 of a reversible motor 95 controlling a damper in the refrigerant line 27. The damper shaft 15 may be coupled to the potentiometer slider to give positive or negative position feedback. A rise in temperature in the fluid leaving line 45 causes an immediate response from resistor 36 which is later modified by thermistor 37 in the opposite direction thus avoiding overshoot. Resistor 61 also modifies the effect of resistor 36 causing the bridge to balance at a lower outlet temperature when the inlet temperature is high and vice versa. A motor overload protective circuit is provided which comprises a current transformer 120 which on small overloads fires a thyristor 131 which clamps the thyristor 75 non conductively thus preventing further load being placed on the compressor motor. Higher overloads will trigger another thyristor 130 which fires thyristor 111 rotating motor 95 to unload the system until thyratron 130 ceases to be triggered in which state the system continues until thyratron 130 also ceases to conduct. In an alternative arrangement the temperature sensitive resistors 36, 61 are serially connected in one arm of an A.C. bridge circuit.