HIGH TEMPERATURE RESISTANCE THERMOMETER TEMPERATURE CONTROLLER
NEW YORK STATE COLL OF CERAMICS ALFRED
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An automatic temperature controller was constructed for use in a furnace in which the specimen can be loaded and unloaded in an atmosphere other than air. The controller, whose sensing element surrounds the temperature and atmosphere control zone, summarizes temperature over a region and maintains temperature with small fluctuations over long periods. The components are a sensing element, Wheatstone bridge unit, galvanometer with capacitor flag, Thermocap relay, and regulating reactor and power contactors. In the operation of the control circuit, the temperature is assumed to be at a set point with the neutral zone of control 1 contactor is closed, shorting out the reactance to allow enough current to satisfy normal demand. At lower temperatures, the resistance of the sensing element is lowered, the Wheatstone bridge unbalanced, the galvanometer deflected to produce less capacity in the Thermocap circuit, and the second contactor closed to short out further reactance and increase the heat. At higher temperatures, the control coil senses the rise and increases its resistance this causes the control system to operate in reverse with 1 contactor closed. If the rise goes too far, the galvanometer defects to increase capacity, the Thermocap opens the first contact, the full reactance is placed in series with the transformer, and heat is decreased. Temperatures are maintained with or - 1 deg C fluctuation within a 200 deg to 1500 deg C range.
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