Boiler control circuit

In order to control the temperature of water in the hot water heating system , the boiler control circuit often uses
the comparison function of the comparator to control the heating equipment. Its control circuit is shown in the figure. In the circuit,
the thermistor pins z and hurricane form a voltage divider, and its divided voltage value is added to the U-
terminal as a reference voltage. The thermistor Riz is placed outside the boiler door. The resistance values ​​of Rn and Rz are selected in this way:
when the external temperature is 16°C, the resistance values ​​of RI2 and Rz are equal. Resistor R, and thermistor
R, t also form a voltage divider, and its divided voltage value is added to the tenth terminal of U. Thermistor R. , placed
inside the boiler t. The resistance values ​​of Rj- and Ri are selected according to the following conditions: when the temperature of the boiler is
88°C, the resistance values ​​of Ru and Rt should be equal. The output of the comparator controls the transistor VT. When the temperature
of the boiler is ≥88°C, the comparator outputs a high level, causing VT to conduct, causing the relay K to close and turn off the heating source of the boiler .