| 摘要 |
Constant condenser pressure is maintained in a refrigeration system by modulating the speed of at least one fan motor of an air-cooled condenser coil in response to the temperature of the refrigerant in the condenser coil, the speed varying directly with temperature. Motor speed variations are achieved by controlling the conduction time of a triac which couples the fan motor to a source of alternating voltage. The triac is triggered into conduction at a phase angle, following the beginning of each half cycle of the alternating voltage, determined by the charging rate of a timing capacitor which charges through a photosensitive transistor optically coupled to an LED. Variation of the refrigerant temperature in the condenser coil changes the light emission of the LED and this in turn varies the charging current translated to the capacitor. The greater the temperature, the greater the charging current and the faster the triac conducts following the start of each half cycle.
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