One of the high-precision non-contact temperature control circuits

When the temperature sensing element R. When using platinum resistor WZB-010, the temperature control range can be from room temperature
to 300℃.
    The main circuit is a bidirectional thyristor V AC voltage regulating circuit. The trigger circuit is a relaxation
oscillator composed of single-junction transistors VTs, etc. Among them, transistor VT4 is used as a variable resistor. A differential amplifier is composed of transistors VTi and VT2. The input
signal of the amplifier is the potential difference between the diagonal lines A and B of the bridge composed of resistors R7 and R8, potentiometer RP, and platinum resistor R. This potential
difference controls the conduction degree of VT4, thereby changing the output pulse of the single-junction transistor trigger circuit and changing the conduction angle of V to achieve
the purpose of automatic constant temperature control.