Topics Discussed
In class, we discussed two new topics essential to doing a proper circuit analysis that would not require us to create a multitude of equations with a multitude of unknowns . We discussed nodal analysis and super nodes in particular. Nodal analysis would allow us to place a voltage on specific nodes in order to reduce the number of equations needed to find various elements within the circuit. Super nodes involved two nodes which had a voltage source.
On day 4 of the ENGR 44 course, we took a quiz involving using KVL and KCL to find a certain voltage across a resistor in terms of other given variables. The quiz was meant to illustrate the difficulty of using such methods to solve for unknown values in a circuit. This provided basis for the discussion of breaking a circuit down into simpler components that allow for less equations to be needed (order reduction). We then went into lab rather than a class discussion on new topics.
Temperature Measurement System Lab
In lab, we attempted to create a circuit that would include a thermostat to change an output voltage by at least 0.5 V. We were provided the thermostat, and we were set to design a circuit that would accommodate three criteria: a required 5 V input voltage, an output voltage that varied at least 0.5 V in a range of 25°C (Room Temperature) to 37° C (Body Temperature), and the output voltage would have to increase as the temperature increased.
We first designed a circuit that would properly adhere to all the specifications required of the lab. (Fig. 1) We found the ideal resistance we would need in or circuit in order to have the best range of resistance as our thermostat changed temperature. (Fig. 2) By taking the derivative of our voltage divider equation, our ideal resistance was found to be 8770 ohms. However, in the lab we 8200 ohms was the closest resistor available, and was thus used. Ideally, our thermostat would operate at 11000 ohms and 7000 ohms at room and body temperature respectively.
We measured the actual resistance of our thermostat at both room and body temperature and calculated their percent difference to our ideal values. Additionally, we measured the actual resistance of our resistor and found it to be 8260 ohms rather than 8200 ohms. We created our circuit and attached it to our Analog Device to give it power and measure voltage across different elements within it. (Fig. 3)
Our circuit functioned properly and measured a different voltage value across our resistor at two different temperatures. (Video & Fig. 4)
Summary
In this lab, we properly constructed a circuit under set conditions that would cause it to have a multitude of different voltage outputs across different temperatures. Our values for voltage output varied by 0.6 V, and our voltage increase as temperature increased. We yielded a percent difference of less than 5% in terms of our output voltage from what we had predicted. Creating this circuit reinforced the concept of voltage dividers and varying resistance elements. We designed the circuit ourselves and successfully created our required thermally dependent circuit.
We first designed a circuit that would properly adhere to all the specifications required of the lab. (Fig. 1) We found the ideal resistance we would need in or circuit in order to have the best range of resistance as our thermostat changed temperature. (Fig. 2) By taking the derivative of our voltage divider equation, our ideal resistance was found to be 8770 ohms. However, in the lab we 8200 ohms was the closest resistor available, and was thus used. Ideally, our thermostat would operate at 11000 ohms and 7000 ohms at room and body temperature respectively.
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| Fig. 1 |
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| Fig. 2 |
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| Fig. 3 |
Our circuit functioned properly and measured a different voltage value across our resistor at two different temperatures. (Video & Fig. 4)
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| Fig. 4 |
Summary
In this lab, we properly constructed a circuit under set conditions that would cause it to have a multitude of different voltage outputs across different temperatures. Our values for voltage output varied by 0.6 V, and our voltage increase as temperature increased. We yielded a percent difference of less than 5% in terms of our output voltage from what we had predicted. Creating this circuit reinforced the concept of voltage dividers and varying resistance elements. We designed the circuit ourselves and successfully created our required thermally dependent circuit.
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