D4 - Notes Nodal Analysis

We started the day with a quiz. It was important to use KCL and KVL to find I1,I1,R1,R2, and R3. I did not finish in time. There were a lot of equations to work through. After the quiz we started on the lab.

Temperature Measurement System:

We use a Thermistor rated at NTC 10K @ 25C for the lab. But first we must do some prelab, our goals were to make it usable with +5 input voltage, voltage varies 0.5V over 25C to 37C, and output voltage must increase as temperature increases.

White board work which describes the things out lined above on what our "resolution" is for this device.

We then measured and worked out the prelab like a regular voltage divider problem.

White board work with the design restrains in a voltage divider problem. Our preliminary design chosen R's are 1.3K and 5.6K ohms. We should get output voltages change of 0.5V. Did not work, later one we got one that did.

We re did some math with the Rth and tried again, this time we found R values that worked. We recorded real values of Rth@24C and Rth@37C which were: 9.6k and 6.75k, which was only 4% off the 10k rated ohms at 25C.

Another picture showing our percent error, our R's this time were 4.6k and 17.5k ohms. Our comparisons to expected results were 0%, our numbers did exactly what we wanted, a change of 0.5V with temperature.

The video below shows the voltage as we input heat into the resistor. It raises the 0.5V needed of the lab, 3.12V to 3.62V. We recorded the fix values actual resistance and did our percent error and the white board.

White page work of the real resistors numbers needed of the lab.

Hand work of the resistors used to get the 0.5V change in a lab.

After the lab we worked on Nodal Analysis, Node voltage method. We use the select a node with a voltage across it, and use KCL first and then sub the voltage laws into it. KVL is (v1-v2)/R1+... and so on for each voltage difference to ground.

White board work of the example gone over class, we found currents in and out and then used KVL and subbed the voltages across each element to the reference node. Used matrix math and got V1 = 13.33V

In summary:
We started the day with a quiz that was hard without the correct usage of KCL and KVL and good choosen nodes. We learn to implent design process with a NTC 10K @25C thermistors that sampled voltage with temperature. We found the whole design process takes iterations and recalculations of the required specifications needed of a design. Lastly we did another example and how useful voltage node analysis can be, for example it would of made the morning quiz doable.