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TEMPERATURE_DIFFERENTIAL_DETECTOR

2014-11-09 17:34  
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TEMPERATURE_DIFFERENTIAL_DETECTOR
This circuit measures temperature differences, not temperature. Once the difference passes a certain threshold, the timer is triggered, activating the solid-state relay.Op amp U1 is placed in a comparator configuration with two thermistors-one located at the ceiling, one at the floor. The IC senses the temperature difference between the ceiling and floor, but is unaffected by the overall room temperature differential increases. The upper thermistor will de-crease in resistance, eventually causing the voltage at pin 2 of U1 to exceed that pin 2 of U1 to go low and trip the timer. This adds hysteresis to the op amp's output, preventing the motor from chatter-ing. When tripped, the timer activates the relay, which activates the fan.