Temperature Measurement System Design

     Temperature Measurement System Design

         A simple temperature measurement system is designed by a Wheatstone bridge circuit and a

difference amplifier. A thermistor as a variable resistor is used in the Wheatstone bridge circuit in

order to show temperature. In other words, the Wheatstone bridge converts the resistance variation of

the thermistor to a voltage variation. Also the op-amp is able to show the temperature by a DC

voltage in its output.

Figure 1: Wheatstone Bridge & an Differential Op-Amp

 The output of the Wheatstone bridge circuit, Vab = Va - Vb, is very small and the differential

amplifier in order to increase this voltage is chosen. The key point, ratio of R2 to R1 is chosen less

than one because output voltage (Vo = 5V) does not go in saturation region.  Vo = (R2/R1)*Vab 

Figure 2: A Schematic of Real Temperature Measurement System

The output voltage from the system is between zero and +/- 20 mV at room temperature (25 C).

Movie 1

When the thermistor becomes hot, the output voltage of the differential amplifier will change.