Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Measuring instruments
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Measuring instruments
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Subject: Basic Electronics
Class: Senior Secondary 2
Term: 2nd Term
Week: 4
Theme: Measuring Instrument And Tools
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Explain the meaning of measuring in strument. Differentiate between analogue and digital measuring in struments. State different types of measuring in strument and the ir respective uses.
by technicians testing audio equipment in studios or in electronics manufacturing. 2.4.
4. DC Power Supply Description: A device that provides a stable, regulated direct current (DC) voltage and current to power electronic circuits for testing and experimentation. They are often adjustable.
Uses: Providing the necessary operating voltage for prototype circuits. Testing components under specific voltage conditions. Charging batteries (some types).
Relevance: Essential in any electronics workshop or lab in Nigeria, from university labs to small startup companies. 2.4.
5. Frequency Counter Description: An electronic instrument used to measure the frequency of a repetitive electrical signal.
Uses: Verifying the operating frequency of oscillators and clock generators. Calibrating radio communication equipment. Measuring the frequency of AC mains supply.
Relevance: Important for radio and telecommunication technicians. 2.4.
6. LCR Meter Description: A specialized instrument designed to measure inductance (L), capacitance (C), and resistance (R) of electronic components with high precision.
Uses: Testing passive components (inductors, capacitors, resistors) for accuracy and tolerance. Quality control in component manufacturing. Characterizing unknown components.
Relevance: Useful in electronics manufacturing and component sourcing in places like Alaba International Market, Lagos. 2.4.
7. Logic Probe Description: A simple, handheld tool used to detect and display the logic state (HIGH, LOW, or PULSE) at a specific point in a digital circuit.
Uses: Quickly troubleshooting digital integrated circuits (ICs) by checking input/output states. Detecting stuck-at faults or oscillating signals. * Relevance: Useful for students and technicians working with microcontrollers and digital systems. 2.
1. Definition of Measuring Instrument A measuring instrument is a device used to determine the magnitude or value of a physical quantity. In electronics, these quantities include voltage, current, resistance, frequency, and capacitance, among others. The primary purpose of these instruments is to provide accurate and reliable data for analysis, troubleshooting, design, and verification of electronic circuits and components. Without them, it would be impossible to quantify electrical parameters, making fault diagnosis and circuit development largely guesswork. 2.
2. Importance of Measuring Instruments Troubleshooting: Identifying faults in electronic circuits by checking voltage levels, current paths, and component resistances.
Design and Development: Verifying that a newly designed circuit performs as expected by measuring its output and internal parameters.
Quality Control: Ensuring that manufactured electronic components and devices meet specified standards.
Safety: Checking for dangerous voltage levels or faulty insulation to prevent electrical hazards.
Maintenance: Regularly monitoring parameters of electronic systems to predict and prevent failures. 2.
3. Analogue vs. Digital Measuring Instruments Measuring instruments can be broadly categorized into analogue and digital based on how they display measurements. 2.3.
1. Analogue Measuring Instruments Definition: These instruments display values continuously by means of a pointer moving across a calibrated scale. The reading is often interpreted by observing the pointer's position relative to the scale markings.
Characteristics: Continuous Output: The display is continuous, representing every possible value within its range.
Pointer and Scale: Uses a mechanical pointer and a physical scale for display.
Parallax Error: Prone to reading errors (parallax error) due to the angle of observation relative to the pointer and scale.
Lower Resolution: Often has lower precision compared to digital instruments due to the limitation of scale markings.
No External Power (often): Many basic analogue meters (e.g., ammeters, voltmeters, ohmmeters) do not require an external power source for operation, drawing power directly from the circuit being measured (except for some advanced VOMs that use batteries for resistance measurements).
Trend Indication: Can easily show trends or rates of change as the pointer moves.
Examples: Analogue Voltmeter, Analogue Ammeter, Analogue Ohmmeter, Analogue Multimeter (VOM - Volt-Ohm-Milliammeter), moving coil meters, some mechanical clocks. 2.3.
2. Digital Measuring Instruments Definition: These instruments display values as discrete numerical digits, usually on an LCD (Liquid Crystal Display) or LED (Light Emitting Diode) screen.
Characteristics: Discrete Output: Displays numerical values in distinct steps (digits).
Numerical Display: Uses an electronic display (LCD/LED) for showing readings.
No Parallax Error: Readings are unambiguous and not affected by viewing angle.
Higher Accuracy and Resolution: Generally offer higher precision and resolution, capable of displaying more decimal places.
External Power Required: Usually requires a battery or external power supply to operate its internal electronic circuits and display.
Additional Features: Often include features like auto-ranging, data hold, and sometimes computer connectivity.
Examples: Digital Voltmeter, Digital Ammeter, Digital Ohmmeter, Digital Multimeter (DMM), digital thermometers, digital clocks, frequency counters. 2.3.
3. Comparison Table: Analogue vs. Digital Instruments | Feature | Analogue Instruments | Digital Instruments | | :--------------- | :--------------------------------------- | :--------------------------------------- | | Display | Pointer on a calibrated scale | Numerical digits on LCD/LED screen | | Reading | Subject to parallax error; skill required | Easy to read; no parallax error | | Accuracy | Generally lower | Generally higher | | Resolution | Lower (limited by scale divisions) | Higher (more decimal places) | | Power | Often no external power needed (passive) | Requires battery/external power (active) | | Cost | Usually less expensive for basic models | Can be more expensive for advanced models| | Trend | Easier to observe changes/trends | Can be harder to observe trends quickly | | Robustness | More prone to mechanical damage | More robust, but sensitive to extreme conditions | 2.
4. Types of Measuring Instruments and their Uses 2.4.
1. Multimeter (Analogue VOM and Digital DMM)
Description: A versatile all-in-one instrument capable of measuring multiple electrical quantities. It combines the functions of a voltmeter, ammeter, and ohmmeter.
Uses: Voltmeter Function: Measures potential difference (voltage) between two points in a circuit.
Connection: Always connected in parallel with models| | Trend | Easier to observe changes/trends | Can be harder to observe trends quickly | | Robustness | More prone to mechanical damage | More robust, but sensitive to extreme conditions | 2.
4. Types of Measuring Instruments and their Uses 2.4.
1. Multimeter (Analogue VOM and Digital DMM)
Description: A versatile all-in-one instrument capable of measuring multiple electrical quantities. It combines the functions of a voltmeter, ammeter, and ohmmeter.
Uses: Voltmeter Function: Measures potential difference (voltage) between two points in a circuit.
Connection: Always connected in parallel with the component or part of the circuit across which the voltage is to be measured. For example, to check the voltage across a light bulb in a torch, connect the meter probes across the bulb.
Units: Volts (V), millivolts (mV).
Ammeter Function: Measures electric current flowing through a circuit.
Connection: Always connected in series with the component or circuit path where current is to be measured. The circuit must be broken to insert the ammeter. For example, to measure current through a charging mobile phone, one would hypothetically connect the ammeter in series with the charging cable (though not practical for users).
Units: Amperes (A), milliamperes (mA).
Ohmmeter Function: Measures electrical resistance of a component or circuit.
Connection: The component must be isolated from the circuit and the power supply must be OFF. Connect the meter probes directly across the component. For example, to check the resistance of a speaker coil or a fuse.
Units: Ohms (Ω), kilohms (kΩ), megohms (MΩ).
Other functions often found: Continuity test (to check if a circuit path is complete), diode test, capacitance measurement, frequency measurement, temperature measurement.
Example 1: Using a Multimeter to Measure Voltage and Resistance Scenario: An SS2 student needs to check if a small 9V battery is still good and also measure the resistance of a 100 Ohm resistor.
Voltage Measurement (Battery):
1. Select the DC Voltage (VDC) range on the multimeter, choosing a range higher than 9V (e.g., 20V range).
2. Connect the red probe to the positive terminal of the battery and the black probe to the negative terminal.
3. Read the value displayed. If it's close to 9V (e.g., 8.5V-9.2V), the battery is good.
Resistance Measurement (Resistor):
1. Ensure the resistor is not connected to any power source or circuit.
2. Select the Resistance (Ω) range on the multimeter, choosing a range suitable for 100 Ohms (e.g., 200 Ohm or 2k Ohm range).
3. Connect the probes across the two leads of the resistor.
4. Read the value displayed. It should be close to 100 Ω. 2.4.
2. Oscilloscope (CRO - Cathode Ray Oscilloscope / DSO - Digital Storage Oscilloscope)
Description: An instrument that displays varying signal voltages as a two-dimensional plot (waveform) against time. It allows visualization of amplitude, frequency, period, and shape of electrical signals.
Uses: Analyzing AC signals, pulses, and complex waveforms. Measuring frequency and period of signals. Determining phase relationships between two signals. Troubleshooting audio, radio frequency (RF), and digital circuits by observing signal integrity. Calibrating electronic equipment.
Relevance: Crucial in advanced electronics labs and repair centers dealing with communication systems, power electronics, and digital circuits. 2.4.
3. Signal Generator Description: A device that produces various electrical waveforms (e.g., sine wave, square wave, triangular wave, pulse wave) at specified frequencies and amplitudes.
Uses: Injecting test signals into electronic circuits to observe their response. Testing amplifiers, filters, and other signal processing circuits. Calibrating other test equipment. Training and experimentation in electronic labs.
Relevance: Used by technicians testing audio equipment in studios or in electronics manufacturing. 2.4.
4. DC Power Supply Description: A device that provides a stable, regulated direct current (DC) voltage and current to power electronic circuits for testing and experimentation. They are often adjustable.
Uses: Providing the necessary operating voltage for prototype circuits. Testing components under specific voltage conditions. Charging batteries (some types).
Relevance: Essential in any electronics workshop or lab in Nigeria, from university labs to small startup companies. 2.4.
5. Frequency Counter * Description: An electronic instrument used 3.
1. Introduction (Teacher Activity)
Engage: Begin by asking students about common measuring devices they use daily (e.g., ruler, clock, thermometer, weighing scale). Relate this to the need for measuring electrical quantities.
Review: Briefly review basic electrical quantities: voltage, current, and resistance, and their units.
Introduce Topic: State the topic for the week: "Measuring Instruments," emphasizing their crucial role in electronics. 3.
2. Concept Explanation and Differentiation (Teacher & Student Activities)
Definition: Present the definition of measuring instruments.
Visual Aids: Display charts, diagrams, or actual examples (if available) of various measuring instruments. Analogue vs.
Digital: Explain the characteristics, advantages, and disadvantages of analogue and digital instruments using the comparison table.
Activity: Divide students into small groups. Provide each group with images or actual (safe, non-powered) examples of both analogue and digital instruments (e.g., an analogue clock vs. a digital watch, an analogue speedometer vs. a digital car display, analogue multimeter vs. digital multimeter).
Student Task: Each group discusses and identifies which are analogue and which are digital, stating at least two reasons for their classification.
Teacher Role: Circulate, guide discussions, and correct misconceptions. Facilitate a brief class feedback session. 3.
3. Types and Uses of Instruments (Teacher & Student Activities)
Instrument by Instrument: Systematically introduce each measuring instrument (Multimeter, Oscilloscope, Signal Generator, Power Supply, Frequency Counter, LCR Meter, Logic Probe).
For each instrument: Display its image or actual device. Explain its primary function and key applications. Emphasize correct connection methods for the multimeter (series for current, parallel for voltage, isolated for resistance). Use simple, relevant Nigerian scenarios where possible (e.g., using a multimeter to check the continuity of a local extension box cable). Demonstration (Teacher Activity - if instruments are available): Demonstrate the safe and proper use of a digital multimeter to measure: DC voltage from a small battery (e.g., AA or 9V battery). Resistance of a resistor or a small light bulb filament (power off). Continuity of a wire or a fuse. Highlight safety precautions (e.g., never measure resistance in a powered circuit, ensure correct range selection).
Note-Taking (Student Activity): Students take detailed notes on the definitions, differentiations, and uses of each instrument.
Q&A: Encourage students to ask questions for clarification. 3.
4. Application and Discussion (Teacher & Student Activities)
Case Study: Present a scenario: "A radio repair technician in Onitsha market needs to fix a faulty radio. He suspects the power supply circuit or a speaker. What instruments would he likely use, and for what purpose?" Student Task: Students, in groups, discuss and propose the instruments and their uses.
Teacher Role: Facilitate the discussion, ensuring students link specific instruments to specific troubleshooting tasks.
Summarize: Conclude the lesson by summarizing the key concepts, reiterating the importance of accurate measurement and the distinct roles of different instruments.
Electronics Repair and Maintenance in Nigerian Markets: In bustling electronics repair hubs like Computer Village in Lagos or Alaba International Market, technicians constantly use multimeters to diagnose faults in mobile phones, laptops, TVs, and other domestic appliances. They measure voltages in power supply units, check continuity of cables, and test resistance of components like speakers or heating elements. More advanced workshops also use oscilloscopes to troubleshoot complex circuit boards, especially in areas like inverter repair or satellite decoder servicing. Electrical Installation and Safety Checks in Homes/Offices: Nigerian electricians use voltage testers and multimeters during new installations or maintenance. They measure AC mains voltage to ensure it's within safe limits (e.g., 220-240V), check for open or short circuits in wiring, and verify the integrity of earthing systems. This ensures the safety of occupants and compliance with electrical codes, preventing hazards like electrocution or fire.
Local Manufacturing and Quality Control: Small and medium-sized enterprises (SMEs) in Nigeria that assemble or manufacture electronic products (e.g., solar chargers, inverters, LED lighting systems, locally made electronic gadgets) integrate measuring instruments into their production lines. They use LCR meters to verify components before assembly, multimeters to test sub-assemblies, and oscilloscopes or signal generators to conduct functional tests on finished products, ensuring quality and reliability for local consumers.