This application can give a construction electronic thermal that can operate from 00 up to 240 C. This circuit can producing output approximately about 500 mV/0 C, that can be read in the voltmeter after calibrate with temperature. To make this application to be a simple circuit, the temperature detector we can give thermystor with negative temperature coefficient (NTC).
This profit for the application, the resistance temperature coefficient is very large, but the temperature coefficient is not constant and the output voltage temperature circuit can’t be linier. In 00 up to 240 area, the linier is enough for a simple temperature.
IC op-amp is connected used to be differential amplifier. Input transmitting by bridge circuit that consists of R1 to R4. The constant of bridge arm can form by R1, R2, R3 and P1, but R4 is to form the variable arm. The voltage in R1 and R2 is 3, 4 volt. Within the increasing of the temperature, the NTC resistance will decrease and the voltage will fall and make the output op-amp increase. If the output can’t precision in 0, 5 V0/C, the value R8 and R9 can appropriately, but both of them have been same.
IC that can use to this application is 741, 3130, or 3140. Compensation capasitor C2 isn’t necessary if we use IC 741, because this IC can compensate. R4 can use NTC 10K, but for small type will give respond faster cause have lower thermal inertial.
