Day April 7 stuff! Temperature Measurement System Design (Weatstone Bridge)

I am not sure where in the class of word files we did the lab of: Temperature Measurement System Design. None of the word files document it but I have pictures and video of the Weatstone bridge working so here they are.

Prelab:
We followed the derivation of the appendix A. We used R1 = R2*Rnorm/R3. The Rnorm is the Thermistor at normal value of 10.7 k ohms at 27 degree C. We decided to use a pot system to cover the range of the Thermistor from 10.7 k ohms to 7.5k ohms.

At the beginning of class we were asked to tell which Op amp was what, the first was a inverting amp since it had a source to negative node, b was inverting same as the first, and C was summing since it had many V's and R's going into the negative node.

 We then started the class with the lab of the day:
Temperature Measurement System Design

White Board work of the prelab, we found V2 = 350mV and Io in terms of Vs. We also drew the circuit schematic for the lab.

Picture of our circuit with Thermistor and potentiometer circuit.

Another picture of our weatstone bridge temperature measuring circuit.

Video below with the range of 2V with the potentiometer range relating to the thermistor. Note the voltage range as the temperature of the thermistor raises thanks to my hand.

 

Video of the range of the voltage working from the Weatstone Bridge.

More white board work below for the lab with R values.

White board work of the weatstone bridge, Rf = 10 M ohms, Rf2 = 1 M ohms, R2 = 10 k ohms.

More white board work, our regular Vout at room temperature is 0.46 V, and Vout when the thermistor is human temperature at -3.54 V.

 For the lab we found our design worked, the Vout had a range of 2V with it dependencies of the thermistor temperature. We had difficulty understand why we couldn't get our Vout regular to be 0 V but got close to it. Overall we happy we got the range desired and change dependent on thermistor temperature aka resistance of Rnorm.


In summary I do not know where this goes in the time line of stuff but here it is and working, we learned on this unknown day that weatstone bridges are hard to design but are rewarding to get working.