Thyristor furnace temperature regulation circuit

The two transistors that make up the differential amplifier are a voltage-divided bias circuit. At the same time, these four resistors are the four
arms of the measuring bridge. Among them, platinum resistor is the best. Its resistance increases with the increase of temperature and decreases with the decrease of temperature. It is also
a temperature measuring element placed in the electric furnace. Changing the resistance of the potentiometer RP can give a furnace temperature. When the furnace temperature is lower than the given temperature. The resistance of R4 decreases and the bridge
loses balance. The base potential of VT2 decreases and the collector current decreases. Since the collector currents of both tubes flow through the emitter resistor (lk),
the emitter potential of the two tubes drops, the collector current of VT1 increases, the collector potential drops, and the base potential of the transistor 3AX31B in the charging circuit
drops. The charging current increases, causing the trigger pulse to advance, the conduction angle of the thyristor to increase, and the furnace temperature to rise. When the temperature is high, all changes
are opposite to the above. Therefore, a differential amplifier can be used to automatically adjust the furnace temperature.