Lab 2 - Equipment Familiarization and Ohm's Law

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University of Texas, Rio Grande Valley *

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Electrical Engineering

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Feb 20, 2024

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Lab 2 CESSAR LECHUGA GERARDO GAMEZ

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 LAB 2: Equipment Familiarization and Ohm’s Law A. OBJECTIVES  Understand the general rules for electrical and electronic laboratory safety  Become familiar with the multimeter and power supply  Be familiar with usage of a breadboard (protoboard)  Verify Ohm’s Law through experimentation of simple electrical circuits  Practice pSpice simulation program for voltage and current divider circuits B. EQUIPMENT  Power Supply  Digital Multimeter (DMM)  Prototype Board  Device Test Leads and Cables C. PARTS  ¼ Watt Resistors: 10 Ω, 330 Ω, 1 kΩ, 2.2 kΩ, 2.7 kΩ, 24 kΩ, 1 MΩ  Hook-up Wires (#20 or #22 gauge solid conductor) D. BEFORE THE LAB 1) Electrical Laboratory Safety Safety is the most important thing to consider in an electronics laboratory environment. Please refer to the Appendix A: Safety (handout in BB’s Course Materials) for details. 2) Equipment Familiarization: Breadboard Generally electronic circuits are either fabricated in the form of an integrated circuit "chip" or made by soldering components onto a printed circuit board. However, experimental circuits are often fabricated using a breadboard, sometimes called a prototyping board or protoboard. Breadboards allow a circuit to be assembled and modified easily without the need for soldering, and generally leave the components (such as resistors) in a re-usable condition. An illustration of a common type of breadboard is shown in the Figure below. 1

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 The long strips along the top and bottom edges are often used for nodes in the circuit that will have a large number of connections (such as the ground or the power supply). The shorter vertical strips are used for other nodes which will have fewer connections. As an example, one way to hook up a simple circuit is shown below. The arrangement shown is just one of many that would work equally well. 2

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Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 3) Equipment Familiarization: DC Power Supply Our Labs are equipped with BK Precision’s Triple Output Programmable DC Power Supply, Model 9130. Go to Blackboard course / Course Material for the instruction manual 4) Equipment Familiarization: Digital Multimeter (DMM) The Digital Multimeter (DMM) is a tool used to measure different electrical parameters, such as voltage, current, and resistance. Throughout the semester you will be heavily relying on this piece of equipment to analyze electrical circuits. Please refer to Manual: Instruments and Parts handout for details on the usage of this device. Proper Connections Completely incorrect measurements will result unless the meter is connected properly to the circuit being measured. You should permanently memorize the following: VOLTMETERS should be connected in PARALLEL AMMETERS should be connected in SERIES Voltage is a potential difference between two points in a circuit; the voltmeter probes are connected to the two points of interest. One speaks of the voltage across a resistor, not through a resistor; therefore the meter should be connected across, that is, in parallel with a resistor to measure its voltage. Current flows through conductors; to measure the current in a conductor the probes must be arranged so that the current that flows through the conductor also must flow through the meter. This means that to measure the current through a resistor, the meter must be in series. The reference positive direction is into the positive terminal on the meter and out of the negative terminal. How to Damage the Meter, your Circuit, and Yourself Several common accidents which can have unfortunate results are: (a) Connecting a voltmeter in series instead of parallel will usually cause the circuit to stop functioning. (b) Connecting an ammeter in parallel instead of series will short out part of the circuit. If it is a high current circuit, components may overheat or catch on fire, the probe tips may melt, and the fuse inside the meter may be blown. (c) Using test leads with poor quality (e.g. cracked or punctured) insulation may result in current passing into the user. 3

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 (d) Leaving a probe plugged into the current jack when attempting to measure a voltage will short out part of the circuit, with results the same as in (b) above. Leaving a probe plugged into the voltage jack when attempting to measure a current will result in the circuit not working. (e) Leaving an extra probe plugged in that is not being used (for example, leaving an extra probe plugged into the current jack when measuring voltage) can result in accidental short circuits. See (b) above. 5) Equipment Familiarization: Resistors Resistors are among the first electronic components that you will be using in an electronics laboratory environment. These components have the capability to block a certain amount of current, depending on their resistance value. There are two ways to know the resistance value of a resistor: 1. Measure resistance using the Multimeter 2. Read and translate the colored bands of the resistor to obtain the resistance value The resistor color code allows you to translate the colored bands into a resistance value. Refer to Figure 1 below. Note that if there is no band for Tolerance, the tolerance is 20% . Figure 1: Resistors and Resistor Color Code 4

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 6) Equipment Familiarization: Test Leads and Cables Some of the most common connectors used in the laboratory are identified in Figure 2 below, along with their names. The first four are used on the ends of leads and cables, while the last two are usually mounted on pieces of equipment. There are a few standard practices related to test leads that are worth noting: a) The outer shell on a BNC conductor is known as the shield , and is almost always at ground potential. Many common pieces of equipment actually tie this connector to the power system ground, so you should not use it for anything else. b) Black leads are generally used for ground connections, while red leads are generally used for power supply connections. On test cables which have a BNC at one end and a pair of alligator clips at the other end, the black clip is always connected to the outer shield while the red clip is connected to the center conductor. c) The insulation on the test probe type cables is usually safe to 1000 volts DC or 750 volts AC, if it is in good condition. If the insulation is dry and crumbly, or has pin holes, the insulation value is greatly reduced. Cables with BNC connectors may have a much lower voltage rating - a few hundred volts. Figure 2: Connector Types and Terminology E. IN THE LAB 1) The breadboard. Understanding its rows and columns Wiring the breadboard. Use the multimeter in sonic continuity mode. Cut two wires 5 to 6 inches long and peel them on both sides Connect the wires to the breadboard terminal posts Lay the multimeter tips on the breadboard wired terminals Insert the idle wire tips on two holes belonging to the same column. Continuity YES / NO Insert the idle wire tips on two holes belonging to the same row. Continuity YES / NO Insert the idle wire tips on two holes belonging to different columns. Continuity YES / NO Insert the idle wire tips on two holes belonging to different rows. Continuity YES / NO 5

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Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 2) Resistor Measurement and Resistor Color Code (a) Read out the nominal values of the given resistors based on the color code. Fill all the values in Table 1. Note: Treat the 4 th colored band as Gold for the resistors in the table. Table 1 Resistor Color Bands-Color 1 2 3 4 Color Bands-Numerical Value 1 2 3 4 10 Ohms Brown Black Black Gold 1 0 1 5% 330 Ohms Orange Orange Brown Gold 3 3 10 5% 1k Brown Black Red Gold 1 0 100 5% 2.2k Red Red Red Gold 2 2 100 5% 2.7k Red violet Red Gold 2 7 100 5% 24k Red yellow orange gold 2 4 000 5% 1M Brown Black Green Gold 1 0 1k 5% (b) The percent tolerance is used to determine the range of resistance levels within which the manufacturer guarantees the resistor will fall. It is determined by first taking the percent tolerance and multiplying by the nominal resistance level. For the example in Table 1, the resulting resistance level is: ( 5% ) ∗ ( 24 kohms ) = ( 0.05 ) ∗ ( 24 kohms ) = 1.2 k ohms Therefore, the range of resistance levels within which this resistor will fall in practice is: 6

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 24 ± 1.2 kohms The above means the resistor is guaranteed to have a minimum resistance of 25.2 kohms and a maximum of 22.8 kohms. Question : What would be the range of resistance levels of the 470 kΩ resistor with 5 % tolerance? Answer: ____470*0.05 = 23.5. range is (446.5,493.5)_k_______________ (c) Set up the Digital Multimeter (DMM) and connect test leads/probes to measure resistance. Then set the range to the lowest one, which is usually about 100 ohms. Connect the test probes together and look at the obtained measurement on the DMM’s display. This is the probe resistance . This means that the probes are not perfect conductors, and will always have a small amount of resistance. This can be neglected when measuring large resistance values, but may be significant when measuring small resistance values. You can correct for probe resistance by subtracting it from subsequent measurements. Probe resistance: 0.10 Ohms (d) Now change the range of the DMM to the highest one, usually in the order of Megaohms. Hold the tip of one test probe in each hand, pinching the metal tip firmly between thumb and finger, and look at the obtained measurement on the DMM’s display. This is your body’s resistance . Afterwards, moisten your fingers slightly and repeat the measurement. Note that if you touch the probes when measuring a resistor component, your body’s resistance is in parallel, which changes the result. For this reason, make sure that you do not touch both ends of the resistor or both probes at the same time during measurements. Body’s resistance : 0.58 MOhms Body’s resistance (with moistened fingers): 200 kOhms (e) Get the following five listed resistors below (Table 2) from the electronics cabinet in the laboratory. Then use the DMM to measure the actual (real) values of these resistors. Fill the values in Table 2. Do not expect to measure exactly the same values as the nominal ones Resistor (Nominal Value) Measured Value 10 Ω 10.11 330 Ω 326.93 1 k Ω 0.9815kOhms 2.2 k Ω 2.1643 kOhms 2.7 k Ω 2.6553 kOhms 24 k Ω 23.881 k Ohms 1 M Ω 1.0024 MOhms 7

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 Table 2 3) Measuring Voltage and Current using the DMM on a Series Circuit (a) Build the circuit shown in Figure 3 on the breadboard. Ask your instructor to check your circuit before turning ON the DC power supply. Figure 3: Two Resistors in Series. Create and run a PSPICE schematic. Display current and voltage on the PSPICE screen (b) Measure the resistance of resistors R1 and R2. Remember to isolate the resistors before attempting to measure their resistance (take the resistors out of the circuit). R1 = 2.1643 kOhms R2 = 0.9815 k Ohms (c) Install back the resistors into the circuit, turn ON the supply, and measure the voltages across resistors R1 and R2. Look at the sign labels: red probe should be on + side, black on - side. V1 = 12.380 Volts V2 = 5.622Volts (d) Next Student 1 , measure the currents through resistors R1 and R2. For current measurements, remember you need to open/break the circuit , else you might damage the fuse inside the multimeter ! Look at the arrow labels: red probe should receive the current, black should release. I1 = 5.728 mADC I2 = 5.728mADC 8

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Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 Notice that currents I1 and I2 equal, or are close, to each other. This is because of the circuit’s setup: the two resistors are placed in a series connection . Series resistors always share the same amount of current . (e) Ohm’s Law states that the voltage V across a resistor R is linearly proportional to the current I through the resistor: V = I·R . Verify the following relationships: V1 = 12.380 I1 x R1 = 12.39 V2 = 5.622 I2 x R2 = 5.622 Does V1 = I1 x R1? Yes Does V2 = I2xR2? Yes ** Show your results to your instructor to obtain a signature. Instructor’s Signature: Jaime Ramos 4) Measuring Voltage and Current using the DMM on a Parallel Circuit (a) Build the circuit shown in Figure 4 on the breadboard. Ask your instructor to check your circuit before turning ON the DC power supply. Figure 4: Two Resistors in Parallel. Create and run a PSPICE sch. Display current and voltage on the PSPICE screen (b) Turn ON the supply, and measure the voltages across resistors R1 and R2. Look at the sign labels: red probe should be on + side, black on – side. V1 = 11.997 V2 = 11.998 Notice that voltages V1 and V2 equal, or are close, to each other. This is because of the circuit’s setup: the two resistors are placed in a parallel connection . Parallel resistors always share the same amount of voltage . 9

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 (c) Next Students 2 , measure the currents through resistors R1 and R2. Again, for current measurements, remember you need to open/break the circuit , else you might damage the fuse inside the multimeter ! Look at the arrow labels: red probe should receive the current, black should release. I1 = 17.770 mADC I2 = 12.240 mA Dc (d) Ohm’s Law states that the voltage V across a resistor R is linearly proportional to the current I through the resistor: V = I·R . Verify the following relationships: V1 = 11.997 I1 x R1 = 38.46 V2 = 11.997 I2 x R2 = 12.01 Does V1 = I1 x R1? No Does V2 = I2 x R2? No ** Show your results to your instructor to obtain a signature. Instructor’s Signature: Jaime Ramos **When done with the laboratory, please return every component to its respective storage. Thank you! F. AFTER THE LAB The After the Lab section is to be completed either at the laboratory or at home, after the main lab work has been finished. Data and results from both In the Lab and After the Lab sections are to be included in the laboratory report. The After the Lab will be graded with equal weight. 1) An 8 V battery is connected to a circuit with a resistance of 2 Ω. What is the current flowing through the circuit? Show your calculations. 8/2 = 4A 2) A current of 7 mA is flowing through a component with a 4 kΩ resistance. What is the voltage being applied to the component? 7x10^-3*4x10^3 = 28Volts 3) 5 volts are being applied to a resistor, which results in a current of 2 mA to flow. What is the resistance of such resistor? 10

Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 V=IR 5/2x10-3 = 2.5kOhms 4) Why do we first need to isolate components from the rest of the circuit when we are about to take resistance measurements of such components? While calculatin the resistance, all the other components connected to the resistance must be isolated, in order to get exact value of the resistance measured 5) For the following questions, consider the circuit in Figure 5. Assume that the DMM has a red probe connected to its positive terminal, and a black probe connected to its negative terminal. Figure 5: Simple electrical circuit  To measure the voltage V 1 , the voltmeter probes connect as follows (circle one option): a) Red probe connects node A, black probe connects node B b) Red probe connects node B, black probe connects node A c) Break circuit at node A, red probe connects source E , black probe connects resistor R 1 d) Break circuit at node B, red probe connects resistor R 1 , black probe connects resistor R 2  To measure the current I 2 , the ammeter probes connect as follows (circle one option): a) Red probe connects Ground, black probe connects node B b) Red probe connects node B, black probe connects Ground c) Break circuit at node B, red probe connects resistor R 1 , black probe connects resistor R 2 11

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Lab 2: Equipment Familiarization and Ohm’s law Electric Circuits I Lab /56 d) Break circuit at node B, red probe connects resistor R 2 , black probe connects resistor R 1  Draw conclusions from § E.1, regarding the electrical continuity of breadboard’s adjacent holes on buses, columns, rows, and sets separated by trenches In the conducted experiments outlined in § E.1, the electrical continuity of the breadboard's adjacent holes has been systematically examined. The insertion of idle wire tips on holes belonging to the same column or row consistently resulted in the detection of continuity, affirming the expected electrical connection. Conversely, when idle wire tips were inserted into holes belonging to different columns or rows, no continuity was observed, indicating the absence of electrical connection. These findings emphasize the reliable electrical isolation between different sets of holes on the breadboard, crucial information for ensuring accurate and effective circuit wiring in electronic experiments. 12

Lab 2 - Equipment Familiarization and Ohm's Law

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