Lab Report Day Four - Temperature Measurement System

1. In the beginning of the class, we finish a quiz about experiencing the different between KCL and Nodal analysis. (in another blog)

 2.  Temperature Measurement System
In this lab, we will design a circuit that has an output voltage depending on temperature. We are going to use a  thermistor,  which changes resistance when temperature changes, and a known resistance in the circuit.
The pre-lab of the experiment. At room temperature, it has 11000 ohm resistance. At body temperature, it has 7000 ohm resistance. We first find the range of the fixed resistor we are going to use. Since we want the temperature drop to be bigger than 0.5 degrees, we find that the value of the fix resistor must be from 4367 ohm to 17633 ohm.

 

We choose a 5.6 k ohm resistor. The actual resistance of it is 5.49 k ohm.

 

 The power supply is 5.0 V.

 

The set up of the experiment. We measure the voltage across the resistor when it is at room temp to be 3.38 V. 

 

 

We measure the voltage across the resistor when it is at body temp to be 2.68 V. 

 

LAB data table: We have a difference in voltage of 0.7 V, which is bigger than 0.5 V. However, our theoretical value of voltage drop should be 0.533 V, so it has a % difference of -31.3%. I guess what causes this happening could be either the room temperature is lower than 25 degrees, or I am too warm (hotter than 37 degrees).

 

Post lab of this experiment. 

We are then asked to design a new circuit that the output sensitivity of the device must be at least 0.1 V/degree. After our calculation, we find that it is impossible to get it. The maximum we can get a difference of 0.563 V in 12 degree’s difference. Our lab data is bigger than the maximum probably the difference in our temperature is higher than 12 degrees. 

 

Here is a video about our experiment. 

 

Summary

Today, we talk more about nodal analysis. We find that using nodal analysis make us have less algebra to do.We use a thermistor that can change its resistance when temperature changes in lab.