Lab Report EE330 L

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Grossmont College *

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330

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Electrical Engineering

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Dec 6, 2023

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EE 330L - ENGR ELECTRONICS LAB Department of Electrical & Computer Engineering San Diego State University LAB REPORT #1 Experiment #1 - Measuring DC Voltages and Currents Members Name’s : Maria Dawood & Joseph Solis Class section : EE 330L-05 Class time : Wed 1300-1540 Date : 09/08/21

Objective: This lab was purposely meant for the students to become more familiar with the equipment and how each of the individual equipment works. For example, digital multimeter (DMM) and the power supply (PS). Therefore, this lab was also meant to make students more comfortable with measuring the voltage and current of a circuit using the equipment and also measuring a resistor’s resistance using the DMM. For that reason, this will allow the students to have a better understanding of how each piece of equipment works, therefore for future labs they would be able to debug the techniques. Theoretical Background : It is very important to understand the basic concepts of how circuits work for this experiment. For example, knowing how each of the individual formulas works, such as Ohm’s law: voltage(V) = resistance(R) * current(I). The second most important concept was when the components in parallel have the same voltage drop and that the current in series remains the same. It is also important to understand how to properly build and ground a circuit to prevent shortages or damage to any of the lab instruments. To start off, we had to measure the current within the circuit, to do that we first had to place the DMM in series with the resistor and set it as an ammeter. However, to measure the voltage of a component of the circuit, the DMM must be placed in parallel with the component and be set as a voltmeter. It is also important to note that the power supply must be connected to the DMM and measured before being connected to the circuit to ensure that the measured, output power is the desired value

Procedure: We initially set the DMM as a voltmeter, connecting it to the power supply (PS) so that we can test and measure the voltage that was coming from the PS. There were several voltages that were tested, 1V, 2.5V, and 6V, to make sure that the DMM set in DC Voltage was reading that number, or at least very close to it. Our measurements of the voltage came out as 1.006V, 2.503V, and 6.005V respectively, and as a result, the DMM was effectively reading the voltage correctly. The next step was to measure each resistor’s nominal value of 1K, 5K, and 10K, by switching the DMM to measure resistance, and connecting the leads to the resistor. Our measured values for each resistor were: 0.989K Ohms for 1K resistor. 4.9992K Ohms for 5K resistor. 9.818K Ohms for 10K resistor. To calculate the percentage difference between the nominal and measured values of the resistors, it was (Measured - Nominal)/Nominal X 100. For the 1K difference, it was 1.06%, 5K was 0.08%, and 10K was 1.82% . After measuring the nominal values, each resistor was inserted into the circuit, one at a time, where the PS connected to the resistor, and the voltmeter was connected

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in parallel to the resistor to measure the voltage across that resistor. The PS was set at 10V and the voltage across each resistor was measured. All voltages that were measured across each resistor came out to be 10V. The circuit now had to be reconfigured a bit, so that the DMM was set up as an ammeter to measure current going through the circuit. This ammeter was connected in series with the rest of the circuit. We first had to make calculated values of the current for the circuit with each of the 3 resistors. The calculations were done using Ohm’s law: V=IR and converted to I=V/R to calculate the current. The calculated current for the circuit with 1K resistor was 10.1065mA For the circuit with the 5K resistor, it was 2.0003mA.

For the circuit with the 10K resistor, it was 1.0185mA. The measured current was done for each of the 3 resistors. For the 1K resistor the circuit current measured was 10.134mA. For the 5K resistor it was 2.004mA. For the 10K resistor it was 1.008mA. We then had to calculate the % difference between our calculated current from using Ohm’s law, and the measured current. For the circuit with the 1K resistor, the difference was 0.2%. For the 5K resistor, the difference was also 0.2%. For the 10K resistor, the difference was 0.88%. Once that was done, the red and black leads of the DMM were switched and the current for each of the 3 resistors had to be measured again. For the circuit with the 1K resistor, the measured current was -10.133mA For the circuit with the 5K resistor, it was -2.003mA. For the circuit with the 10K resistor, it was -1.008mA. The final step of the experiment was to use 2 DMMs, one set up as a voltmeter and the other as an ammeter. The power supply was switched to a triple power supply to use the +20V output for positive voltage and -20V output for negative voltage. We only needed 2 resistors for this part so we ended up picking the same 5K and 10K resistor. This part of the experiment required us to connect both the ammeter and voltmeter at the same time, and as for the power supply, we had to measure the current from voltage power supply intervals of 0.5V from 0V to 3V, both in positive and negative voltages.

Data Sheet Q/A: 1. Why is the difference in terms of connections and internal resistance between a voltmeter and ammeter? Explain why MUST a voltmeter and ammeter behave differently? A voltmeter is connected in parallel with an element in order to measure the voltage across that element. This is because any parts that are in parallel have the same voltage in a circuit. An ammeter is connected in series with the part you want to measure the current because the current going through parts that are in series is the same. The internal resistance of a voltmeter needs to be high so that there's as little current as possible that will not reduce the reading of the voltage. For an ammeter, the internal resistance needs to be as little as possible

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instead so that there’s little to no restriction of current flowing in the circuit that will not reduce the amp reading. 2. Did switching the DMM leads change the voltage or current in the circuit under test? It changed both the current value and voltage from positive to negative. 3. Did switching leads change the direction of current flow through the DMM? Yes it did, the output became negative 4. Did the voltage across the resistor change when it changed from 5Ωto 10Ω? Why or why not? No, because the power supply is giving a 10V, and due to Ohm’s Law, since there’s only one resistor in the circuit and the current flow is the same throughout the circuit, the voltage across that one resistor will always be 10V. 5. Did your data match the Ohm’s law? Yes, it did match. Since the equation for Ohm’s law is V=IR, we simply needed to divide the voltage by the resistance, and the measured values more or less matched the calculated ones. 6. Did switching the DMM’s leads change the direction of the current flowing through X’? Switching the DMM lead did change the direction of the current flowing through X, which is evident by the fact that the measured current in X for all 3 values has the opposite sign compared to the 3 values measured in the previous step. 7. How do your plots change for different values of Y’? Calculate the slope for each value of Y and relate the 2 slopes to the corresponding values of Y.

To calculate the slope, take two points on the graph, with the Y(vertical) value/X(horizontal) value, subtract and divide the numbers. For Y1 for 5K resistor it was (0.59 - -0.59)/(3 - -3) = slope of about 0.197 mA/V. For Y2 for 10K resistor, it was (0.3 - -0.3)/(3 - -3) = slope of 0.1 mA/V. Both of the slopes make sense considering that these values would be the current under a 1V supply in a circuit. Where a circuit with a 1V and a 5K resistor, under OHm’s Law, would have a 0.2mA current, and a circuit with a 1V and a 10K resistor would have a 0.1mA current. Conclusion: For this lab, we were able to be familiar with the equipment and how each one works. We were also able to find the current and voltage at a given Ω. We were also able to identify where the error was occurring during the lab. The main equipment for this

experiment was using the power supply (PS) and the digital multimeter (DMM). We had to use Ohm’s law: voltage(V) = resistance(R) * current(I) to find the voltage while also using the PS and the DMM. During the experiment we had to answer some questions about our answers and while doing that it gave us more knowledge on why our answers were either correct or there was an error.

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