Sample Prelab - DC 2 & 3 ESET 210

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Texas A&M University *

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210

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Electrical Engineering

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Feb 20, 2024

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Pre-Lab Experiment DC 2&3 1 Kirthika Piratla Pre-Lab Experiment DC 2 & 3 Kirthika Piratla 231007008 Section 507

Pre-Lab Experiment DC 2&3 2 Kirthika Piratla Pre-Lab Experiment DC 2: Resistors and the Color Code Purpose: In this experiment, color code resistance readings from the given resistors are compared to the resistance values measured using the VOM and the DMM. Resistors are used to regulate the flow of current in electronic circuits. The wattage of a resistor is indicated by its size. The color code identifies the resistive value and the percent tolerance of the resistor, and will be compared to measured multimeter and milliammeter values to test the accuracy of the reading. Materials: Resistors: - 1 1-MΩ, 1-W film resistor - 1 1-MΩ, 2-W film resistor - 1 1-MΩ, ½-W film resistor - 1 6.8-Ω, 91-Ω, 220-Ω, 3.3-kΩ, 10-kΩ, 470-kΩ, 1-MΩ, ¼-W film resistors Instruments: - 1 VOM (Volt-Ohm-Milliammeter) - 1 DMM (Digital Multimeter) Procedure: 1) Body Size: Draw the physical sizes of the resistors and label them according to their wattage rating. Note the ratios of the sizes of the 2-W compared to the 1-W and the 1-W compared to the ½-W. 2) Color Code: Determine the color bands on each resistor in the kit and note the colors in order. Note their associated numerical values according to a resistor color code chart. Multiply the percent tolerance by the nominal resistance level to get the uncertainty, and apply the uncertainty to the nominal resistance to get the maximum and minimum resistance levels. Read the resistance levels of each resistor using the DMM using the appropriate scale for each measurement and find the difference between the nominal and measured values using the following equation. Observe whether each resistor fell under the tolerance range. % 𝐷𝑖???????? = ???𝑖?𝑎? −??𝑎????? ???𝑖?𝑎? | | | | × 100% 3) Repeat Step 2 using the VOM. 4) Body Resistance: Guess the resistance of your body between the ends of your hands. Then, measure and note the actual resistance using the DMM. Wet your fingers and firmly hold one lead in each hand. Calculate how much voltage would be required to pass a current of 10 mA through your body using the following equation. 𝑉 = 𝐼𝑅 5) Meter Resistance - Voltmeters: Note the Ω/V rating beneath the VOM scale. The internal resistance of each setting can be found using the equation below. Then, find the internal resistance of the VOM using the DMM as an ohmmeter and find the percent difference between the calculated and measured values. 𝐼?????𝑎? ???𝑖??𝑎??? = ?𝑎?𝑖??? ????𝑎?? ??𝑎?𝑖?? × Ω/𝑉 ?𝑎?𝑖?? Use your lab neighbor’s DMM to measure the internal resistance of each dc voltage scale of your DMM and compare its specified resistance to its measured resistance. If the reading is more than the max resistance that the DMM can read, truncate the value to the max resistance. 6) Meter Resistance - Ammeters: Measure the resistance of each dc current scale of the VOM using the DMM as an ohmmeter. Then, using the VOM as an ohmmeter, measure the resistance of each current scale of the DMM. Observe which meter would least disturb the network with its resistance. Ideally, meter resistance should be as small as possible.

Pre-Lab Experiment DC 2&3 3 Kirthika Piratla Pre-Lab Experiment DC 3: Ohm’s Law Purpose: In this experiment, Ohm’s Law will be put to the test by comparing the measured and calculated values of a circuit’s current, I . The current flow of a circuit is directly proportional to the voltage and inversely proportional to the resistance, as dictated by Ohm’s Law. In other words, the voltage is the cause, the resistance is opposition to the cause, and the current is the effect. Materials: Resistors: - 1 1-kΩ, 3.3-kΩ, ¼-W film resistors Instruments: - 1 VOM (Volt-Ohm-Milliammeter) - 1 DMM (Digital Multimeter) - 1 dc Power Supply Procedure: 1) Setting the Output Voltage of a dc Power Supply with a DMM and VOM: Connect the DMM to the dc power supply. Oscillate through various voltage levels on the power supply using the DMM. Between each voltage level setting, remove the DMM and measure the terminal voltage using the VOM. Note your measurements. Make sure to choose the appropriate scales of the DMM and the VOM for desired accuracy. Calculate the percent difference in your readings using the following formula. % 𝐷𝑖???????? = 𝐷?? − 𝑉?? 𝐷?? | | | | × 100% For the next set of voltages, start by connecting the VOM to the dc power supply and repeat the previous steps. Between each voltage level setting, remove the VOM and measure the voltage using the DMM. Calculate the percent difference again, this time switching the DMM and VOM variables. Observe how the percent differences vary across instruments. Next, reverse the leads of the meter; reset the voltage to 5V using the DMM, disconnect the DMM, connect the red lead to the B terminal and the black lead to the A terminal. Observe the effect on the reading. Repeat this process with the VOM. Note which instrument appears to be more accurate. 2) Ohm’s Law (Determining I ): The current of a dc circuit will be found using Ohm’s Law and direct measurement. Construct the given circuit in the lab manual ( Fig 3.8. ) using the DMM as a milliammeter. Current should enter the positive terminal and leave the negative terminal. Note the measured value of R. Then, set the DMM on the high milliammeter scale. The red lead should be moved to the A terminal. Using the VOM, adjust the power supply voltage such that the voltage across the resistor is 2V. The red lead must be connected to the terminal of higher potential and the black lead to the terminal of lower potential. Choose an appropriate scale for the milliammeter while maintaining 2V as the voltage across the resistor. Record the value of I from the DMM. Then, calculate the value of I using the Ohm’s Law formula given below. 𝑉 = 𝐼𝑅 Calculate the percent difference between the measured and calculated values of I . % 𝐷𝑖???????? = 𝐷?? − ?ℎ?'? ?𝑎? 𝐷?? | | | | × 100% Repeat this procedure for various voltages. Note the percent differences as an indicator of how close Ohm’s Law can get to measured values. 3) Plotting Ohm’s Law and R: Plot measured values of I versus V . Explore the relationship between V , I , and R using these graphs and Ohm’s Law. Follow the lab manual’s instructions in plotting and calculating this relationship.

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