Day 4 (Temperature Measurement lab)

There was a quiz that morning and I would like to share pictures of myself right before, during, and after said quiz.

Right before

During

After

The quiz wasn't actually that bad. It was just a lot of variables to juggle around and using traditional KVL and KCL techniques to solve them were a little challenging for the allotted time. The quiz was a great lead to the new technique that we would learn but first was the lab.

The lab was the Temperature Measurement lab and it continued on the concept of a circuit that had sources dependent on external factors. This time it was a temperature probe (thermistor) that would adjust its resistance value based on the external temperature. With one constant resistor in series with the variable resistor, it was possible to measure a voltage and correlate that to a certain temperature.

In the pre-lab we were asked to find a resistor that would be placed in series with the thermistor to have a change in .5 volts when the thermistor goes from 25 to 37 degrees celsius. The resistor that we found accomplished this was 3500 ohms and it was expected that there would be a 1.25 difference in voltage. It was designed so that it was more accurate than the expected .5 volt difference.

 

The resistance of the thermistor at room temperature, roughly 25 degrees, was 10.48 kiloohms and at body temperature, roughly 35 degrees, the resistance was 6.34 kiloohms. The voltage across the resistor was measured at room temperature, roughly 25 degrees, as 1.26 volts and the voltage across the resistor at body temperature was 1.80 volts. The difference in voltages at the two different measurements was .527 volts which is significantly lower than the calculated value. Here is a picture of the set up, the results, and a video of the voltage change based on temperature.

The redesigned system of having a .1 volt/C change on the circuit proved to be mathematically impossible with resistors that had real values. The resistor would require some imaginary resistance.

The maximum change in voltage that this circuit can accomplish with this thermistor is .0457 volts.

A new circuit analysis technique that was introduced was the nodal analysis which set some essential node to a ground and then made arbitrary voltage values at every other essential node. Current was rewritten as differences in voltage over a resistance. This circuit was analyzed using nodal analysis. The arbitrary voltage values were 13.3 volts and 20 volts respectively.