This circuit is a temperature indicator circuit or differential instrumentation amplifier using a transducer bridge. This circuit is calibrate in degrees Celsius or Fahrenheit. In the circuit used buffer in and points for exact voltage of and points. Because gain is always 1 of buffer circuit. Then the output voltage of buffers is input voltage of differential amplifier.
The differential amplifier is difference voltage of and points using 741 Op Amp. When temperature is increased then resistance is also decreased and output voltage is decreases and when temperature is decreased then resistance is also increased and output voltage is increases.
The temperature indicator is a circuit that indicates of temperature in degrees Celsius or Fahrenheit. The temperature is inversely proportional to the resistance or transducer.
Fig.01 - Temperature indicator
In the circuit used as the transducer in the bridge circuit is a thermistor and replaced output voltmeter to temperature indicating meter. Then temperature indicating meter is calibrate in degrees Celsius or Fahrenheit.
The bridge can be balanced at a desired reference condition, for instance 250C. As the temperature varies from its reference value, the resistance of the thermistor changes and the bridge become unbalanced. This unbalance bridge in turn produces the meter movement.