EE330L - Report 1

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San Diego State University *

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330L

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Electrical Engineering

Date

Apr 3, 2024

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Uploaded by MasterIceGuanaco6

Experiment 1 - Measuring DC Voltage and Current EE 330L Blake Pearson Steven Kourani 1

The objective of this experiment was to familiarize ourselves with the use of 2 lab devices, the power supply (PS) and the digital multimeter (DMM), to measure the voltage (V), and the current(I) and understand their characteristics. This experiment aims to provide a practical understanding of these electrical quantities, as well as the concept of reference direction. By utilizing the DMM to measure DC voltage and current. Why is the difference in terms of connections and internal resistances between a voltmeter and ammeter? Voltmeters measure voltage across components and require high internal resistance to draw minimal current. However, ammeters measure the current flowing through a circuit and, in order to minimize any influence on the measured current, they require low internal resistance. The fundamental difference is essentially in internal resistances; low for ammeters to precisely measure current flow, and large for voltmeters to limit current draw. My lab partner and I began the experiment by reading the essential background information to start the experiment. We started by gathering the required materials and began setting up the DMM and the PS as seen here: 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 measure the power supply voltage using a voltmeter and built the circuit as shown in figure 1: We then measured 3 voltages using these parameters and then swapped the leads to observe the following results: Power Supply Voltage (V) Measured Power Supply Voltage (normal connections) (V) Measured Power Supply Voltage (swapped connections) (V) 1 0.992 -0.992 2.5 2.491 -2.491 6 5.998 -5.998 Did switching the DMM leads change the voltage or current in the circuit under test? Did switching leads change the direction of current flow through the DMM? Initially when reading the DMM the measured power supply voltage was positive and the value of the voltage stayed constant. After switching the connections the measured power supply 3

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voltage became negative. The polarity change is a reflection of how the DMM interpreted the recorded voltage, not a reversal of the circuit's current flow. The lead switch has no effect on the circuit's real voltage and current values because the DMM understands it based on its magnitude and direction of the signals. We were then given 3 resistor values 1kΩ, 5kΩ, 10 kΩ, and measured their DMM values in isolation and measure the voltage across each resistor using the same circuit configuration as Figure 1 and we got: Nominal Value of X (kOhm) Measured Value of X (kOhm) %-diff between nom. & meas. resistances Measured Voltage of X (V) 10 9.841 -1.59% 10.002 5.1 4.998 -2% 10.002 1 0.986 -1.4% 10.001 We calculated the percent difference between the resistor’s nominal value and the DMM value using this equation: /100. % ?𝑖?? = ((??𝑎𝑠. − ?𝑜𝑚.)/?𝑜𝑚.) Did the voltage across the resistor change when it changed from 5kOhm to 10kOhm? Why or why not? The voltage across the resistor did not change due to the fact as seen in figure 1, the voltmeter is in parallel with the resistors. Therefore, the voltage is constant in a parallel circuit. Following this, we connected the resistor and DMM as seen in the figure below. We used the switch on the power supply as the switch seen in the circuit diagram. Once the circuit was set 4

up we began measuring the current across X with the DMM for each resistor value with the power supply set at 10V. During the measurements we recorded our data in the table below. After completing the measurements we computed the percent difference between the calculated and measured values to determine any discrepancies that may have occurred between the theoretical Ohm’s law computation and the experimental values. Voltage in X (V) Measured Value of X (kOhm) Calculated current in X (Ohm’s Law) (mA) Measured current in X (mA) %-diff between calc. & meas. currents 10 0.986 10.00 10.163 1.63% 10 4.998 2.00 2.001 0.05% 10 9.841 1.00 1.006 0.6% Did your data match Ohm’s law? We found that our data did match Ohm’s Law very closely. There is a minor percent difference between the measured values and calculated values, but this was always less than 2%. It's safe to conclude that small factors that exist in non-ideal circuits, such as wire resistance and DMM internal resistance, contributed to this difference. 5

Next, we switched the black and red leads of our DMM to measure the current labeled i2 seen within figure 3. Besides this change, we made no other adjustments to the circuit measured previously. After these adjustments, we proceeded to switch the power supply back on and measure the current that was flowing through the DMM, which we recorded in the table below. It is apparent from the data in the table that switching the leads of the DMM did not change the direction of the current that was flowing through element X. It simply measured the current with a different reference position. Measured Value of X (kOhm) Voltage across X (V) Measured current in X (mA) 0.986 10 -10.163 4.998 10 -2.001 9.841 10 -1.006 Following this, 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 6

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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 1 was a 9.841 k resistor and our Y 2 was a 4.998 kΩ resistor. We measured the voltage and current in steps of 0.5, starting from -3 and going to +3. The table below shows the results of this experiment. POS Volts Voltage & Current Neg Volts Voltage & Current in Y 1 in Y 2 in Y 1 in Y 2 0 -0.642mV, -0.0554μA 0.416mV, 0.092μA 0 -0.159mV, -0.003μA -1.314mV, -0.234μA 0.5 0.509V, 51.867μA 0.487V, 97.104μA -0.5 -0.495V, -49.883μA -0.478V, -95.051μA 1 1.004V, 102.081μA 0.966V, 0.193mA -1 -0.981V, -99.788μA -0.992V, -0.199mA 1.5 1.481V, 0.150mA 1.481V, 0.296mA -1.5 -1.472V, -0.149mA -1.451V, -0.290mA 2 1.975V, 0.201mA 1.951V, 0.390mA -2 -1.972V, -0.200mA -1.964V, -0.393mA 7

2.5 2.483V, 0.253mA 2.450V, 0.490mA -2.5 -2.476V, -0.252mA -2.465V, -0.493mA 3 2.968V, 0.302mA 2.931V, 0.587mA -3 -2.971V, -0.302mA -2.930V, -0.586mA After collecting all the data it is necessary to construct a scatter plot with a line of best fit to help interpret the data. Looking at the graph below, we can make many conclusions about how the resistor value contributes to the voltage and current output. Questions: How do your plots change for different values of Y? Calculate the slope for each value of Y and relate the two slopes to the corresponding values of Y. 8

As seen from the graph and the table, the plotted line represents the proportional relationship between Voltage-Current which represents the resistance components Y1 and Y2. As shown in the plot, Y1's values are approximately double those of Y2, therefore we can see that the currents flowing through Y1 is approximately half of what Y2 is, reaffirming ohm's law and showing that as resistance increases, current decreases. And in the plot this corresponds to a steeper slope for Y1 compared to Y2. Conclusion: This Lab experiment allowed my partner and I the opportunity to become familiar with the applications of two lab devices; the digital multimeter (DMM) and the power supply (PS). By measuring voltage (V) and current (I), we were able to obtain important knowledge about the properties of these variables, which improved our understanding of the fundamental principles of these circuits. Moreover, this experiment gave us useful hands-on experience with the idea of reference direction. Which is important for accurate measurements. As well as using the DMM to measure DC voltage and current which will be important for future labs. 9

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