Lesson Plan. Preparation

Transcription

1 Course Title: Construction Technology Session Title: Electrical Test Equipment Performance Objective: Lesson Plan Upon completion of this assignment, the student will be able to demonstrate and explain how to use both a digital and an analog multi-meter. Specific Objectives: Identify and describe the display area, the function switch, and the leads/jacks on a digital multimeter. Adjust the mechanical zero and interpret a reading on the voltage scale, and the resistance scale of an analog multimeter. Given an expected measurement, set the function and range switches of an analog multimeter and adjust the zero on the ohms scale. Know how to use a multimeter for a variety of purposes, including checking for continuity across a circuit, measuring resistance, current, frequency, AC and DC voltage, and capacitance. Explain the operation and appearance of the following pieces of test equipment: Ammeter; Voltmeter; Ohmmeter; Continuity tester; and Voltage tester. Preparation TEKS Correlations: This lesson, as published, correlates to the following TEKS. Any changes/alterations to the activities may result in the elimination of any or all of the TEKS listed Advanced Building Maintenance Technology (6) Students will demonstrate knowledge of how to properly select, inspect, use, and maintain common electrical test equipment and: (a) explain the operation of various test equipment such as ammeter, voltmeter, ohmmeter, volt-ohm-multimeter, wattmeter, megohmmeter, frequency meter, power factor meter, continuity tester, voltage tester, recording instruments, and cable-length meters; (b) explain how to read and convert from one scale to another using test equipment; (c) explain the importance of proper meter polarity; (d) define frequency and explain the use of a frequency meter; and (e) explain the differences between digital and analog meters. Copyright Texas Education Agency, All rights reserved. 1

2 Interdisciplinary Correlations: English: 110.xx(6) - Reading/word identification/vocabulary development (A) expand vocabulary development through wide reading, listening, and discussing; 110.xx(6) - Vocabulary Development 110.xx(6)(A)...expand vocabulary through...listening and discussing 110.xx(6)(B)...rely on context to determine meanings of words and phrases such as figurative language, idioms, multiple meaning of words, and technical vocabulary xx(15) - Listening/speaking/critical listening 110.xx(6)(B)...rely on context to determine meanings of words and phrases such as figurative language, idioms, multiple meaning of words, and technical vocabulary... Instructor/Trainer References: Instructional Aids: 1. Electrical Test Equipment PowerPoint Presentation 2. Electrical Test Equipment PowerPoint Outline 3. Ohm's Law Handout 4. Student Lab 1 Handout 5. Student Lab 2 Handout 6. Student Lab 3.Handout Materials Needed: 1. Electrical devices used for demonstrating test equipment. (A simple dc circuit). Switch. Light Bulb. Battery. 2. Pencil and Paper. Equipment Needed: 1. Digital Multimeter 2. Amp Meter 3. Voltage Meter 4. Projector and PC Learner Student should be familiar with Ohms' Law and Electrical Theory. Copyright Texas Education Agency, All rights reserved. 2

3 Introduction Introduction (LSI Quadrant I): Say: Electricity is a very important commodity in our society. It is used in every aspect of our lives. It powers our lights, computer, machinery, and it helps preserves our foods. So when there are problems with electricity, everyone looks to the electrician to resolve these problems. That is when a good knowledge of electrical test equipment is important. Ask: What would be some the things to consider when troubleshooting and testing electrical circuits and devices for problems? Outline (LSI Quadrant II): Outline PowerPoint presentation may be used in conjunction with testing devices to enhance learning concepts. LEARNING OBJECTIVES Voltmeter use. Ammeter use. Ohmmeter use. Use of Ohm's Law. How to measure voltage. Characteristics of voltage: existing between two points. Selection of proper meter range. How to measure resistance. Selection of proper meter range. How to measure current with a multimeter. How to check a multimeter's internal fuse. Guided Practice (LSI Quadrant III): Application 1. Teacher demonstrates how to use testing meters. 2. Teacher supervises lab activities and maintains visual support. Copyright Texas Education Agency, All rights reserved. 3

4 Independent Practice (LSI Quadrant III): Students works on lab assignments using the different testing meters the demonstrate knowledge of these devices and testing electrical circuits. Lab 1: Testing a electrical circuit for voltage Lab 2: How to test current in a circuit. Lab 3: How to test resistance in a circuit. Summary Review (LSI Quadrants I and IV): Q: What indication on a multi-meter would you select to read voltage in a circuit? A: Set your multi-meter's selector switch to the highest-value of AC or DC volt position available. Q: What precautions should one take before reading continuity in a electrical device? A: A continuity test should be done when current is NOT present. Always unplug the device or turn off the main circuit breaker before attempting a continuity test. Evaluation Informal Assessment (LSI Quadrant III): Monitor students progress in lab assignments an re-teach as needed. Formal Assessment (LSI Quadrant III, IV): Use electrical test equipment exam and exam key. Use electrical test devices skills test. Extension/Enrichment (LSI Quadrant IV): Students that have mastered the lab assignments, will be able to complete most lab assignment with minimum supervision. Copyright Texas Education Agency, All rights reserved. 4

5 Lab 1: Testing Electrical Circuits with the Multi-meter How To Test the Voltage of an Outlet Working with live electrical current can be very hazardous. Testing voltage output requires working with electrical current. Do not attempt this measurement without the proper tools and safeguards. A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analog multimeters indicate these quantities by means of a moving pointer over a printed scale. 1. To measure the voltage at an electrical outlet requires the use of a multimeter. Always test your test equipment for proper operation before use. Set the multimeter to AC voltage. The markings may appear as VAC, AC V, or a V beneath a wavy line. 2. Choose the AC voltage closest to the voltage you will measure. Standard current in home and businesses in the USA is in the range of 110 to 120 volts. Some circuits used for equipment such as dryers, air conditioners electric stoves, ovens and other large equipment may use voltage in the range of 220 to 240 volts. 3. These heavy-duty circuits can be identified by their non standard outlet plugs. While grasping the insulated portion of the probes (never touch the metal conductor during testing) place one probe into each of the two terminals. The multimeter will display the voltage. 4. Carefully remove the probes, being careful not to touch the metal part of the probes to anything or each other. The voltage should test in the range of 110 to 120 volts for most circuits. Copyright Texas Education Agency, All rights reserved. 5

6 Lab 2: Testing Electrical Circuits with the Multi-meter How To Test the Voltage of an Outlet Working with live electrical current can be very hazardous. Testing voltage output requires working with electrical current. Do not attempt this measurement without the proper tools and safeguards. A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analog multimeters indicate these quantities by means of a moving pointer over a printed scale. 1. To measure the voltage at an electrical outlet requires the use of a multimeter. Always test your test equipment for proper operation before use. Set the multimeter to AC voltage. The markings may appear as VAC, AC V, or a V beneath a wavy line. 2. Choose the AC voltage closest to the voltage you will measure. Standard current in home and businesses in the USA is in the range of 110 to 120 volts. Some circuits used for equipment such as dryers, air conditioners electric stoves, ovens and other large equipment may use voltage in the range of 220 to 240 volts. 3. These heavy-duty circuits can be identified by their non standard outlet plugs. While grasping the insulated portion of the probes (never touch the metal conductor during testing) place one probe into each of the two terminals. The multimeter will display the voltage. 4. Carefully remove the probes, being careful not to touch the metal part of the probes to anything or each other. The voltage should test in the range of 110 to 120 volts for most circuits. Copyright Texas Education Agency, All rights reserved. 6

7 Lab 3: Electrical Test Equipment Neon Light Tester The simplest and least expensive tester is the neon 2-wire volt tester. 1. Put one of the leads on a ground reference (box screws, neutral side of a plug, neutral or white wire, etc.) and the other lead on the hot wire (hot side of a plug, black or red wire, etc.) 2. If the neon light glows, then you have voltage at the outlet. Copyright Texas Education Agency, All rights reserved. 7

8 OUTLINE 1 Electrical Trades Electrical Test Equipment 2 Learning Objectives Voltmeter use How to measure voltage Ammeter use How to measure current Ohmmeter use How to measure resistance Use of Ohm's Law 3 Voltage Testing Devices Voltage testers are used to measure or check the presents of voltage in an electrical circuit. Wiggy Voltmeter 4 Types of Voltage Testers 5 Types of Voltage Testers 6 Using a Voltage Tester 7 Using a Voltage Tester 8 Using a Voltage Tester 9 The Ammeter It is essential that electricians be able to use clamp-on ammeters, or multimeters, for in-place troubleshooting of motors and controllers as well as other circuits. Many clamp-on ammeters can be used to measure voltage and resistance as well as current. They come in various sizes with selections of scales that make them extremely versatile tools. 10 Using the Ammeter The amps flowing through the cable registers on the LCD display. Because an amp clamp does not plug in to the line, there is no current loss and the reading is more accurate. Clamp-on transformer jaws. Take current readings without interrupting service. Clamp around conductors up to 1" (2-54cm) in diameter or 500MCM. 2" (5.08cm) Or 2000MCM for 1000 ampere models. It allows current draw to be measured quickly and accurately. The jaws of the clamp are clamped around one of the cables and the motor is started. Copyright Texas Education Agency, All rights reserved. 8

9 Outline Page 2 11 Using the Ammeter An amp clamp is a non-invasive method of checking current draw with any electrical set up. The jaws of the clamp are spring loaded so that they can be clamped around a cable; usually the positive lead in a DC electrical set-up. It works by measuring the impedance of the current flowing through the cable. This method has many benefits. It is easy to set up; you only have to be able to access one cable to be able to take a reading. It is non-invasive because you do not have to plug anything in to the line between battery and speed controller, or between controller and motor. Plug in methods are cumbersome (shunted meters or wattmeters), especially in the field, and always have some associated power losses which make the reading a little inaccurate. 12 Testing Electrical Circuits with the Multi-meter A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analog multimeters indicate these quantities by means of a moving pointer over a printed scale. Analog multimeters tend to be less expensive than digital multimeters, and more beneficial as learning tools for the first time student of electricity. Connect the black lead to the common (- ) hole. This may well already be done, depending on the type of meter you use. Connect the red lead to the volts (+) hole. Be careful, if this lead Is placed in the wrong hole (ohm or amp) it can cause permanent damage to the meter. This may well already be done, depending on the type of meter you use. Turn the selector switch to AC volts (usually red). If there are Multiple selections, use the highest setting possible (if power unknown) or go one level higher than the estimated power. Some digital meters have "Auto- range" and don't require any selection apart from AC volts. 13 Measuring Current in a Circuit Current is the measure of the rate of electron "flow" in a circuit. It is measured in the unit of the Ampere, simply called "Amp," (A). The most common way to measure current in a circuit is to break the circuit open and insert an "ammeter" in series (in-line) with the circuit so that all electrons flowing through the circuit also have to go through the meter. Because measuring current in this manner requires the meter be made part of the circuit, it is a more difficult type of measurement to make than either voltage or resistance. Some digital meters, like the unit shown in the illustration, have a separate jack to insert the red test lead plug when measuring current. Other meters, like most inexpensive analog meters, use the same jacks for measuring voltage, resistance, and current. Copyright Texas Education Agency, All rights reserved. 9

10 Consult your owner's manual on the particular model of meter you own for details on measuring current. When an ammeter is placed in series with a circuit, it ideally drops no voltage as current goes through it. In other words, it acts very much like a piece of wire, with very little resistance from one test probe to the other. Consequently, an ammeter will act as a short circuit if placed in parallel (across the terminals of) a substantial source of voltage. If this is done, a surge in current will result, potentially damaging the meter: 14 Measuring Resistance in a Circuit Resistance is the measure of electrical "friction" as electrons movethrough a conductor. It is measured in the unit of the "Ohm," that unit symbolized by the capital Greek letter omega (Ω). Set your multimeter to the highest resistance range available. The resistance function is usually denoted by the unit symbol for resistance: the Greek letter omega (Ω), or sometimes by the word "ohms." Touch the two test probes of your meter together. When you do, the meter should register 0 ohms of resistance. If you are using an analog meter, you will notice the needle deflect full-scale when the probes are touched together, and return to its resting position when the probes are pulled apart. The resistance scale on an analog multimeter is reverse-printed from the other scales: zero resistance in indicated at the far right-hand side of the scale, and infinite resistance is indicated at the far lefthand side. There should also be a small adjustment knob or "wheel" on the analog multimeter to calibrate it for "zero" ohms of resistance. Touch the test probes together and move this adjustment until the needle exactly points to zero at the right-hand end of the scale. Digital multimeters set to the "resistance" mode indicate non-continuity by displaying some non-numerical indication on the display. Some models say "OL" (Open-Loop), while others display dashed lines. If you are using a digital multimeter, you should see a numerical figure close to 10 shown on the display, with a small "k" symbol on the right-hand side denoting the metric prefix for "kilo" (thousand). Some digital meters are manually-ranged, and require appropriate range selection just as the analog meter. If yours is like this, experiment with different range switch positions and see which one gives you the best indication. Trade & Industrial Education 3 15 Measuring Resistance in a Circuit Connect the meter's test probes across the resistor as such, and note its indication on the resistance scale: If the needle points very close to zero, you need to select a lower resistance range on the meter, just as you needed to select an appropriate voltage range when reading the voltage of a battery. Resistance is the measure of friction to electron flow through an object. The less resistance there is between two points, the harder it is for electrons to move (flow) between those two points. Given that electric shock is caused by a large Copyright Texas Education Agency, All rights reserved. 10

11 flow of electrons through a person's body, and increased body resistance acts as a safeguard by making it more difficult for electrons to flow through us, what can we ascertain about electrical safety from the resistance readings obtained with wet fingers? Does water increase or decrease shock hazard to people? Be sure to never measure the resistance of any electrically "live object or circuit. In other words, do not attempt to measure the resistance of a battery or any other source of substantial voltage using a multimeter set to the resistance ("ohms") function. Failing to heed this warning will likely result in meter damage and even personal injury. 16 Using Ohm s Law 17 Summary Working with live electrical current can be very hazardous. Testing voltage output requires working with electrical current. Do not attempt this measurement without the proper tools and safeguards. It is essential that electricians be able to use clamp-on ammeters, or multimeters, for in-place troubleshooting of motors and controllers as well as other circuits. Always test your test equipment for proper operation before use. A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. There are two types of multimeters, the digital and the analog meters. Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analog multimeters indicate these quantities by means of a moving pointer over a printed scale. Ammeters are use to check current in a circuit. An amp clamp is a non-invasive method of checking current draw with any electrical set up. Copyright Texas Education Agency, All rights reserved. 11

12 Copyright Texas Education Agency, All rights reserved. 12