Circuit diagram of electronic thermostat for liquids

The thermistor K273 can be used to monitor and regulate the temperature of a fluid , which is always immersed in the liquid. A bridge circuit is composed of a differential amplifier. The principle of selecting the resistance of the bridge arm is that the voltage drop on the thermistor is higher than the voltage drop of the emitter resistor of the differential amplifier until the temperature adjusted by switch S. In this way, the base of transistor T1 is turned on with a positive potential relative to the emitter, T2 is turned off, and the relay is released. Its normally closed contact rl connects the heating element. Once the temperature on the thermal element reaches the set temperature, the differential amplifier is switched and the heating stops.

Main technical data: Working voltage: 220V, 50Hz Adjustable temperature: 25, 60 or 95 degrees Celsius Temperature deviation of the circuit (at 20 to 70 degrees Celsius): 0.5 degrees Celsius Temperature difference between the regulator on and off: 1.5 degrees Celsius.

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