March 5, Temperature Measurement System and quiz 1

Preclecture Quiz

 Lab
prelab calculation
Based on our calculation on the white board, to make the change of voltage greater than 0.5. the range of resistor is (4366.7, 17653), so we choose 10k resistor.

 Actual Circuit

Measurements, the voltage at 20 degree is 2.31V and at 37 degree(body temperature) is 2.90V

Measurement at low temperature 20 degree

Measurement at high temperature.

measured resistance at 20 degree

We measured that at 20 the resistance is 11.5k ohm and at 37 degree the resistance is 6.4k ohm.

In this experiment the predicted voltage drop should be 0.72V while the actual voltage drop is 0.62V which is 13.8% off the theoretical value.
The difference may due to we are not heated the thermistor to 37 degree or we are not cooled it to room temperature because we repeat this lab many times. So the experimental value is smaller than the theoretical value.
The error could happened in the measurement of resistance or measurement of voltage.

Post lab
We expect that from 37 degree to 20 degree the votage drop at least 0.1(37-20)=1.7V.
However, based on our data, we put the equation of change of voltage. We plot the function in computer and find out the maximum value of change is 0.727V, which we need to choose a 8k ohm resistor. So there is no way we can design a ciucuit that meet the 0.1V per degree reqiuement.
If we use 8K ohm resistor the results should be 0.0428 ohm per degree. That is the largest we can get.

DEMO

Summary
In this lab we know how to design a circuit to fit certain requirement. And we also practice voltage divider. To make the lab better, we should measure the resistance as soon as we get it and heated as long as possible and measure the resistance right after measure the voltage. So that we can minimize the influence by temperature change.