EE330L - Report 2

pdf

School

San Diego State University *

*We aren’t endorsed by this school

Course

330L

Subject

Electrical Engineering

Date

Apr 3, 2024

Type

pdf

Pages

Uploaded by MasterIceGuanaco6

Experiment 2 Simple DC Circuits with Resistors and Resistive Sensors EE 330L Blake Pearson Steven Kourani 1

The objective of this experiment is to provide a comprehensive understanding of series and parallel DC circuits, along with verifying fundamental circuit properties. My lab partner and I had to become familiar with resistors, potentiometers, and a photoresistor as well as a thermistor. Additionally, we learned to convert non-electrical parameters such as light intensity and temperature into electrical resistance using simple sensors. Through the task of this experiment we will reinforce our knowledge of Kirchhoff's voltage and current laws, series and parallel circuits, resistor combinations, and voltage dividers. We first started by creating this circuit as shown in figure 1: 2

The starting connection was taking the red lead and connecting each end to the positive terminals of the PS and DMM. By taking the green lead we would ground the connection to the negative terminal of the PS. We then connected the black lead to the green lead in the PS and the other side to the negative terminal of the DMM. We established a voltage source and measured the voltage through both X and Y resistors. %-Difference Nominal value of X = 2.2kΩ Measured value of X = 2.148kΩ -2.36% Nominal value of Y = 5.1kΩ Measured value of Y = 4.994kΩ -2.16% Calculated value of V 1 = 3V Measured value of V 1 = 3.006V 0.2% Calculated value of V 2 = 7V Measured value of V 2 = 6.995V -0.07% We calculated the percent difference between the calculated voltage value and measured value using this equation: /100. And we notice that the % ?𝑖?? = ((𝑀?𝑎𝑠. − 𝐶𝑎𝑙?.)/𝐶𝑎𝑙?.) difference is very minimal, showing that the calculated and measured values are very close together. Since the difference is very minimal, our data supports the conclusions made by Kirchoff’s voltage law. This further proves its significance within circuits and circuit theory. Using the same resistors we then used a different set up as shown from figure 2: 3

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

%-Difference Calculated Value of i 1 = 4.545mA Measure Value of i 1 = 4.660mA 2.53% Calculated Value of i 2 = 1.96mA Measure Value of i 2 = 2.002mA 2.14% Calculated Value of i 3 = 6.506mA Measure Value of i 3 = 6.657mA 2.17% Calculated Value of X || Y = 1.537 kΩ Measure Value of X || Y = 1.501kΩ -2.34% Calculated Value of X+Y = 7.3 kΩ Measure Value of X+Y = 7.144kΩ -2.14% What can be seen again is that our percent difference is minimal. Notice that our calculated values are very similar to our measured values. Since this setup was testing the validity of Kirchoff’s current law, we can conclude from our percent difference that our data supports the theory of KCL. Furthermore, we also tested the mathematical rules regarding parallel and series resistors. Since our percent difference was minimal for this data, our experiment also supported the parallel and series resistor rules. 4

We proceeded to hook up the circuit as seen in figure 4. In order to do this, we swapped the leads on the ammeter DMM and set up a new DMM to measure voltage across the resistor. Furthermore, we stitched out power supply to the triple output power supply in order for us to utilize the +20V and -20V ports. Once the circuit was set up and the power supply configured, we measured voltage and current across two different resistors. Our Y values we 1kΩ , 2.2kΩ , and 3.3kΩ resistors. We measured the voltage and current in steps of 0.2 V, starting from -1 and going to +1. The table below shows the results of this experiment. POS Volts Current in Y Neg Volts Current in Y 1kΩ 2.2kΩ 3.3kΩ 1kΩ 2.2kΩ 3.3kΩ 0 -0.564 -0.272 -0.166 0 -0.167 -0.083 -0.081 0.2 0.198mA 84.19 60.645 -0.2 -0.191m A -100.131 -59.831 0.4 0.355mA 0.174mA 0.127mA -0.4 -0.365m A -0.185m A -0.126m A 0.6 0.564mA 0.272mA 0.183mA -0.6 -0.563m A -0.275m A -0.187m A 5

0.8 0,747mA 0.349mA 0.244mA -0.8 -0.734m A -0.355m A -0.233m A 1 0.923mA 0.438mA 0.301mA -1 -0.923m A -0.437m A -0.301m A From both our data and the graph of our data it can be concluded that our measured values satisfy Ohm’s law. We see that the slope of our lines decreases as we increase the resistance of the resistor. This is because of the linear relationship of Ohm’s law. Furthermore, we notice that our slope is equal to the reciprocal of the resistance (offset by 1000 because of current being in mA). If we consider increasing the resistance of the resistor, then we can infer from our data that the slope of the line would decrease. 6

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Following this, we measured the resistance of each resistor used in the procedure above and then compared this to their actual values. The following data is the comparison of the nominal and measured values of the resistors used. Nominal (kΩ) Measured (kΩ) Percent Difference 3.3 3.245 -1.66% 2.2 2.146 -2.45% 1 0.994 -0.6% We notice that the percent difference between our measured and nominal values is minimal. From this we can conclude that the DMM is accurate in measuring the resistor value and that the tolerance of the resistor is acceptable for the experiments conducted above. This further validates the data that was provided in the previous section of the experiment. The next part of this experiment was measuring the resistances of the photoresistor under varying levels of light intensity, encompassing Covered Completely, Slightly Covered, Ambient, and then used the 4 light levels. To achieve these different light levels, we covered the photoresistor with our hands to simulate darkness, then positioned it near the light source from our Iphones to simulate the 4 light levels. Using both the light meter and a Digital Multimeter (DMM), we recorded the photoresistor's resistances at each light intensity level below: X = light level (f-c) Y = resistance (Ω) Covered Completely 5923 Slightly Covered 2836 Ambient 425.9 7

iPhone Light @ 25% 174.95 iPhone Light @ 50% 110.53 iPhone Light @ 75% 87.46 iPhone Light @ 100% 70.26 What can be determined from the data is that the plot is relatively linear except for when the photoresistor is in darkness. If we consider the points where the photoresistor is in darkness then we see that it will actually decay exponentially. This behavior is in line with theoretical behavior for a photoresistor. Furthermore, if we look at our slope of the linear portion we see that the photoresistors light sensitivity is around -79.87 Ω/per level. Ultimately, this data shows key characteristics about photoresistors and the various effects that light has on it. It is important to note that because of the exponential decay of a photoresistor, detecting darkness is far more obvious than changes in brightness. We then proceeded to measure the resistances of the thermistor at different temperatures by altering its temperature using two distinct methods: the first was using both our body 8

temperatures by touching the thermister, the second was to have more heat by using the Soldering Iron. We used a thermometer type device to measure the different temperatures and we used the DMM as well to measure the thermistor's actual resistances at the 5 temperature points shown in the table. X = temp ( o C) Y = Resistance(Ω) X = temp ( o C) Y = Resistance(Ω) 25.1 9375 65.8 5881 29.5 8437 36.1 7605 48.2 7206 Analyzing our data, we can determine that a thermistor is decaying exponentially as-well. This observation lines up with the accepted theory that as we increased the heat exposed to the thermistor, it’s resistance decreased with it. We can calculate the temperature coefficient of the 9

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

thermistor at around 35 celsius and determine that it is around -126 Ω/ ℃ . We understand that the thermistor is non-linear in nature because of the wide range of temperatures that it must measure and the physical properties of a thermistor. Next, we set up a voltage divider. We chose nominal values fo 6.8kΩ and 3kΩ for our R 1 and R 2 respectively. Once the voltage divider was set up, we measured the voltage across the resistor R 2 . The following table shows the resulting data. Nominal Measured R 1 6800 Ω 6685 Ω R 2 3000 Ω 2967 Ω V 3.080 V First, we should compute the theoretical voltage output of our voltage divider. Performing this computation gives us the expected voltage as 3.060V. If we compare this voltage to our measured voltage, we see that the values are very similar. To be specific the percent difference between these two values is 0.006%. This percent difference is so minimal that we can conclude that the voltage division equation is accurate to a high degree. Similarly to the previous procedure, we set up a voltage divider with the goal of the output voltage being approximately ⅓ of the source voltage. In order to achieve this we utilized the voltage division equation and algebra to calculate the value of R 1 and R 2 . We came to the conclusion that if we chose R 2 as 2000Ω we would need R 1 to be 1000Ω in order to achieve this ⅓ ratio. The following data is a result of this experiment. Nominal Measured R 1 2000 Ω 1968 Ω 10

R 2 1000 Ω 997 Ω V 3.336 V After computing the theoretical voltage of our voltage divider, we see that the nominal output should be 3.333V. Notice that our measured voltage is 3.336V. From this minimal difference we can conclude that the voltage division equation is accurate. Furthermore, the minimal difference in our measured and nominal value can be attributed to either the accuracy of the DMM or the tolerance of the resistors used. We see that the measured resistor value is slightly off of our nominal values which contributes to the percent error. Next, we wanted to test the theoretical knowledge of a potentiometer. In order to do so, we hooked up our DMM and power supply to the potentiometer and measured the voltage at different potentiometer levels. The following table is the data that was collected from this experiment. R 1 @ 0 % 10.001 V R 2 @ ~25 % 7.331 V R 3 @ ~50 % 5.032 V R 4 @ ~75 % 2.729 V R 5 @ ~100 % 0.112 mV 11

From our data, we can conclude that potentiometers are somewhat linear. This is a known fact as potentiometers translate a linear rotation into a linear change in resistance. Our data lines up with the known information about potentiometers, and further confirms this linearity property. One thing to recognize is that the potentiometer is one of the few linear elements we looked at in this lab. Finally, the last experiment that we conducted was to set up a voltage divider that utilized a photo resistor. To set this up we utilized the photoresistor as element R 1 in the voltage divider. We then picked a resistor that would provide ~5V at ambient light level. Once these were set up in series and our DMM was connected across R 2 we began measuring the voltage output at different light levels. The following table shows the data that was collected from this experiment. X = light level V = light sensors’s output (volts) Ambient 5.257 iPhone Light @ 25% 5.997 iPhone Light @ 50% 6.158 12

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

iPhone Light @ 75% 6.247 iPhone Light @ 100% 6.321 In analyzing our data, we see that our voltage divider met our design goal. At ambient lighting it had a voltage output of around 5 Ohms. Furthermore, as light increased the output voltage also increased. This is the proper case for our design as the increase in light would cause the resistance of the photoresistor to decrease. With a decrease in resistance across the photoresistor, that caused an increase in voltage that we measured on our voltage divider output. While at first this may seem counterintuitive, we must recall that on our voltage divider the photoresistor is R 1 and we have a constant resistor R 2 in which the voltage is being measured across. This result lines up with the voltage divider equation as a decrease in R 1 means a smaller denominator for the ratio and hence a bigger number to be multiplied by V in . 13

Conclusion This lab enabled us to have a comprehensive understanding of series and parallel circuits with the help of understanding fundamental concepts of Kirhcoffs’s voltage and current laws, by implementing different resistor connections, and observing the behavior of voltage dividers as well as current dividers. Additionally, our understanding of the photoresistor, and the thermistor highlighting their responsiveness to light and heat respectively demonstrated significant change to the resistance showcasing their decay exponentially. Enhancing our knowledge of circuit theory and sensor applications. 14