Temperature limit Relay

This circuit, is basically a resistance ? sensing window switch, except that the ?resistor? takes the form of an NTC thermistor and the circuit thus responds to temperature. TH1 must have a resistance in the range 500ohm - 9Kohm. RV1 is used to set half ? supply volts on the RV1 ? TH1 junction at the ?mean? temperature.
Temperature limit Relay - schematic

Part List R1=4.7Kohm TH1=NTC thermistor 500ohm.....9Kohm Q2=BC214L R2=2.2Kohm D1-2=1N4148 RL1=12V Relay >120ohm RV1-2-3=10Kohm pot. D3=1N4001

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