3/9 Temperature Measurement System

The picture is the quiz we had in the beginning of the class.
The way we solved it is shown in the picture, and this method will be changed later in this post.

Temperature Measurement System


To do this lab, we need to find a value for R in the circuit above such that Vout changes by at least 0.5V over the specified temperature difference.

Through these two pictures, we found R should be a value between 4367 ohms and 17633 ohms. Our group pick R to be 10K ohms.
According to the circuit in the lab manual, we had the lab set up in the picture below:

Equipment:
1. breadboard
2. some wires
3. voltmeter
4. Thermistors
5. 10K ohms resistor


From the data above, the measured thermistor resistance at room temperature is 9.9k ohms and body temperature is 5.9k ohms.
The actual resistance of 10k ohms resistor is 9.8k ohms
We measured the voltage across the resistor  at room temperature = 2.46V
                       the voltage across the resistor at  body temperature = 3.09V
We plugged the measured thermistor resistance into the equation, and we got Vout changes = 0.6337V (calculated)
The actual Vout changes = 3.09 - 2.46 = 0.63V (measured)
The %error we got is about 0.58%, which is very close to what we expect.
The video below is how we found the Vout changes:

This question is the same the quiz we had in the beginning of the class but using a different method called Nodal Analysis (Node Voltage Method).
Steps to determine Node Voltages:
1. Select a node as the reference node(ground). Assign all the others node v1, v2, ....
2. Apply KCL to each node but without reference node.
3. Use Ohm's Law to express the branch currents in terms of node voltages
4. Solve the equations
(from Day 4 Notes Nodal Analysis )
We can see that it is much easier than the way we did in the beginning of the class.

The next example is nodal analysis with voltage sources.

Basically, it is the same as what we did in the last example. The only difference is we had "supernode" this time.
The definition of supernode: A supernode is formed by enclosing a (dependent or independent) voltage source connected between two nonreference nodes and any elements connected in parallel with it.(from Day 4 Notes Nodal Analysis)
In the picture, we treated v2 and vx as a supernode, which will make this problem much easier compared to doing this problem with the method we did before this class.

Summary

We learned a different method (Nodal Analysis) to solve the problems with resistors and voltage sources in them. This method will at least make the problems 50% easier than before. Because the less unknowns we have, the easier the problems are. For the lab, we learned how to create a circuit that can produce different Vout depending on the temperature that the thermistor is. This circuit can be used in real life, like circuit protection and volume control.