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electric pumps and air compressors. A form of pressure switch is also used to operate equipment that automatically feeds livestock, says Calhoun. Three types of time controls are widely used - time clocks, re-cycling timers, and timers. Time clocks auti omatically control poultry house lighting, automatic, feeders for poultry, crop dryers and other equipment. ' Teh and 12-minute reclying timers are popular for controlling mechanical ventilation systems for poultry and livestock. One type operates equipment for the desired amount of time and then cuts off. Photo-electric relays are sensitive to changes in light. They automatically turn yard lights on at dusk and off at dawn. They are adapted for counting operations, an d many other applications. Other important electrical control devices a r e f 1 o at switches, limit switches, so
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