Thermistor temperature automatic detector circuit

Shown is an electric heater that uses a thermistor as a temperature measuring element for automatic temperature control. The temperature control range is from room temperature to
the maximum temperature measurement value of the thermistor , and the measurement accuracy can
reach 0.1℃.
    The thermistor RI used for temperature measurement has a positive temperature
coefficient. It is connected as a bias resistor in
the differential amplifier circuit composed of VT1 and VT2
. When the temperature changes, the resistance of the thermistor
changes, causing VT1 to
The change in the collector current
causes a change in the charging current of the capacitor C through the diode VD2, changing the charging speed, thereby causing a phase shift in the output pulse of the single-junction transistor and changing
the conduction angle of the thyristor vs. This adjusts the heating current in the electric heating wire to achieve the purpose of automatically detecting and controlling the temperature .