THE UNITED STATES OF AMERICA AS REPRESENTED BY THE UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
发明人:
DAWSON, WALTER F.
申请号：
US19740491098
公开号：
US3918636(A)
申请日:
1974.07.23
申请国别(地区):
美国
年份:
1975
代理人:
摘要：
An apparatus is disclosed for effecting precision control over the temperature of water utilized in laboratory experiments. In its preferred form, the apparatus constitutes a Wheatstone bridge which incorporates a thermistor in one arm and an adjustable resistance in another arm. The thermistor is adapted to be disposed in a body of water, the temperature of which is to be monitored. Through suitable adjustment of the adjustable resistance means, the bridge can be balanced at a given temperature. Upon deviation of the monitored temperature from the given balancing temperature, an output voltage signal is provided, the polarity of which being indicative of the direction of temperature deviation. The output voltage signal is amplified and passed to a relay circuit which includes a diode rectifier such that the circuit is responsive to only one polarity of the amplified output voltage signal. Upon actuation, the relay circuit will serve to generate a trigger signal. A load circuit is provided which constitutes a water temperature controlling apparatus, such as a heater, a solenoid valve or the like, the load circuit further including an energizing semiconductor switch such as a triac which assumes a conductive state to energize the load in response to the trigger signal. Energization of the load circuit effects a thermal change in the body of water. A manually operable switch, such as a double pole double throw switch, is provided for selectively inverting the polarity of the output voltage signal from the Wheatstone bridge so that the temperature controlling load circuit is energized either upon an increase or a decrease in the monitored temperature of the body of water. A plurality of such apparatus can be provided powered from a single DC voltage supply, such that control can simultaneously be effected over a plurality of different bodies of water.
