Electric heating furnace automatic temperature controller

 The automatic temperature controller of the electric heating furnace is shown in Figure 1-25. This circuit forms a closed
loop from temperature detection and output control; when the temperature increases, the output voltage increases. When it increases to the voltage of the preset temperature value, the output stops and the heating stops;
conversely , when the temperature decreases, when it decreases to the preset temperature value When the temperature is below the set temperature, heating will start automatically. The thermocouple TC is directly connected to
the ① and ⑩ pins of IC1 and sent to the internal differential amplifier for amplification. It is output from the ⑨ pin and drives the solid state relay VS to conduct through VT. The
heating resistance wire RL is energized and heated. When heated to the preset temperature, Output stops. Pin ③ sets the input and output hysteresis voltage, which
is achieved by connecting resistor R to pin ⑨. The smaller the resistance value, the greater the hysteresis voltage. The control temperature is determined by the voltage of pin ⑧
. The relationship between pin ⑧ voltage, temperature and TC is shown in Table 1-3.
    AD594/595 also designed a "zero compensation" circuit (not used here). Pins ⑩ and ⑩ are alarm and indication outputs
. The internal transistors are open-circuit c and e poles, which can directly drive LED or small relays. VD1 is connected here as a working
indicator light to indicate the start and stop of heating.