Measuring Instruments in Electrical and Mechanical Systems
Content Standards and Performance Standards
Content Standards
The learners demonstrate an understanding of the concepts and principles in performing mensuration and calculations.
Performance Standards
The learners perform mensuration and calculations following safety precautions
Learning Competencies and Objectives
Learning Competency: Interpret the readings in different measuring instruments.
Volt-Ohm-Milliammeter
Multi-purpose instrument for measuring voltage, resistance, and current in electrical circuits.
Tachometer
Device used to measure rotation speed (RPM) of a shaft or disk in mechanical systems.
Oscilloscope
Electronic test instrument that graphically displays varying signal voltages as a function of time.
Ampere Meter
Instrument that measures electric current in a circuit.
Learning Objectives: Explain the function and uses, identify the parts, and interpret the readings of these measuring instruments.
Introduction to Measuring Instruments
1
Overview of different measuring instruments used in electrical and mechanical systems.
2
Importance of these tools in providing accurate measurements to ensure system functionality and safety.
Volt-Ohm-Milliammeter (VOM)
Function
A combined device used to measure voltage (V), resistance (Ω), and current (A) in a circuit.
Uses
Voltage measurement across two points.
Uses
Current measurement in series with the circuit.
Uses
Resistance measurement to check for continuity or faults in a component.
Tachometer
Measures the speed of rotation (revolutions per minute or RPM) of a rotating object or machine.
Automotive Applications
Used in vehicles to monitor engine RPM, helping drivers maintain optimal performance and avoid exceeding safe speed limits.
Industrial Machinery
Applied in factory settings to ensure machinery operates within specified rotation speeds for safety and efficiency.
Electric Motor Monitoring
Portable tachometers help technicians verify the rotation speed of electric motors and troubleshoot performance issues.
Oscilloscope
Basic Function
Displays a visual representation of electrical signals, showing how voltage changes over time.
Waveform Analysis
Used to analyze the waveform of signals in electrical circuits.
Diagnostics
Diagnoses issues with signal integrity, frequency, and amplitude in electronics.
Ampere Meter (Ammeter)
Ammeter Function
Measures the current (in amperes) flowing through a circuit.
Professional Applications
Helps monitor the flow of current in circuits to prevent overloads and ensure components are functioning properly.
Clamp Ammeters
Modern ammeters often use clamp designs that allow for current measurement without breaking the circuit.
Key Vocabulary: Volt-Ohm-Milliammeter (VOM)
Definition
A versatile instrument that combines three functions: measuring voltage (V), resistance (Ω), and current (A). It is used in various forms to test circuits and components.
Key Terms
Voltage: The electric potential difference between two points in a circuit.
Resistance: The opposition to the flow of electric current, measured in ohms (Ω).
Current: The flow of electric charge, measured in amperes (A).
Key Vocabulary: Tachometer
Definition
A device used to measure the rotational speed of an object, typically in revolutions per minute (RPM).
Key Terms
RPM (Revolutions Per Minute): The unit of rotational speed, indicating how many complete revolutions an object makes per minute.
Speed: The rate at which an object moves or rotates.
Rotational Motion: Movement around a central point or axis.
Key Vocabulary: Oscilloscope
Definition
An electronic test instrument that graphically displays varying signal voltages, showing how the voltage changes over time.
Key Terms
Waveform: A graphical representation of a signal's variation with time.
Amplitude: The height of the waveform, representing signal strength or voltage level.
Frequency: The number of wave cycles per second, measured in Hertz (Hz).
Signal: A varying electrical current or voltage that carries information.
Key Vocabulary: Ampere Meter (Ammeter)
Definition
A device used to measure the electric current (in amperes) flowing through a circuit.
Key Terms
Current: The flow of electric charge through a conductor.
Amperes (A): The unit of measurement for electric current.
Series Connection: A type of circuit connection where components are arranged in a single path, and current flows through them one after another.
General Vocabulary Related to Measuring Instruments
Calibration
The process of adjusting a measuring instrument to ensure its accuracy.
Measurement
The process of obtaining a value (e.g., voltage, current, speed) using an instrument.
Accuracy
The degree to which a measurement agrees with the true or standard value.
Resistance
A property of a material or component that resists the flow of electric current.
Frequency
The rate at which something occurs, particularly used to describe wave cycles in signals or sound waves.
Preparation for Measurement: Zero Adjustment
Check Zero Position
Before making any measurements, make sure that the meter pointer is in the zero position.
Adjust if Necessary
If not at zero, turn the zero adjuster so that the pointer may align right to zero position.
Correct Wrong Pointer Setting
If pointer is not at zero, turn the adjustment screw (zero corrector screw) in counterclockwise direction until the pointer is at zero voltage range.
Checking Ohmmeter Accuracy
Set VOM Range
Set VOM to x1 ohm or x10 ohm selector resistance range.
Connect Test Probes
Check the accuracy of the ohmmeter by touching two test probes together.
Observe Reading
Hold the two probes simultaneously and observe the reading, which should be zero ohms when probes are touching.
Important Notes on Using VOM
1
The teacher should limit coverage on the Voltmeter, Ohmmeter and Milli-ammeter function of the tester.
2
The teacher should highlight the logarithmic ohmmeter scale and illustrate the crowded and uncrowded scales of the ohmmeter.
3
The teacher should demonstrate how to use the VOM's ohmmeter function and range multipliers.
4
The teacher must thoroughly clarify the processes for reading the multi-tester scale, putting the range and scale in relation to the range multiplier.
Safety Reminders When Using Ohmmeter
Passive Circuits Only
Ohmmeter function is only for passive circuit and is connected across the circuit or in parallel with the circuit or component to be measured.
Power Off
Always ensure the circuit is powered off before connecting the ohmmeter.
Parallel Connection
Connect the ohmmeter in parallel with the component being measured, not in series.
Proper Range Selection
Select the appropriate range for accurate measurements.
Group Activity: Research and Discussion
Form Groups
Divide the class into four groups, each assigned one of the following instruments:
Group 1: Volt-Ohm-Milliammeter (VOM)
Group 2: Tachometer
Group 3: Oscilloscope
Group 4: Ampere Meter (Ammeter)
Research Questions
What is the function of the instrument?
How is it used in practical applications?
What are the specific measurements it provides?
Where can this instrument be commonly found?
How does it contribute to troubleshooting or diagnostics?
Group Activity: Presentation Preparation
Create Visual Aids
Create a poster that visually explains the function and uses of the instrument.
Prepare Demonstration
Develop a skit or demonstration showing the instrument in use.
Organize Information
Prepare a short presentation that details the main points about your assigned instrument.
Practice Presentation
Rehearse your presentation to ensure clear communication of key concepts.
Group Activity: Presentation Guidelines
Each group should include these five key elements in their instrument presentations:
Describe the Instrument
Each presentation should cover a complete description of the instrument and clearly explain its purpose.
Explain Working Principles
Explain how the instrument works, focusing on the basic principles and mechanisms behind its operation.
Show Real Applications
Provide real-life examples of how the instrument is used in different fields and industries.
Create Visual Materials
Include visual aids such as posters, live demonstrations, or slides to enhance understanding.
Prepare for Questions
Be prepared for a Q&A session after your presentation to address inquiries from classmates.
Activating Prior Knowledge: Circuit Analysis
Question 1
You are using a voltmeter to measure the voltage across a 10-ohm resistor in a circuit powered by a 12V battery. The voltmeter reads 8V.
What does the reading of 8V indicate about the circuit?
What could be the cause of the lower-than-expected voltage reading?
Question 2
You set up a simple circuit with a 100-ohm resistor and a 9V battery. You place an ammeter in series with the resistor and measure the current. The ammeter reads 0.09 A.
What is the current flowing through the circuit?
Is this value what you would expect from Ohm's Law? (Use Ohm's Law: I=V/R)
Activating Prior Knowledge: Troubleshooting
Question 3
You use a multimeter to measure the resistance of a 220-ohm resistor. The multimeter shows a resistance value of "OL."
What does the reading "OL" mean?
What could be the possible reasons for this reading?
Question 4
In a simple circuit, you measure the voltage across a resistor and get a reading of 0V, even though the power supply is working. The ammeter reads 0A.
What could be the reason why the voltage and current are both 0?
What should you check in the circuit to troubleshoot the issue?
Activating Prior Knowledge: Current Measurement
Question 5
You are measuring the current in a circuit using an ammeter. The reading shows 0.5 A when the circuit is supposed to be carrying 1 A based on the components and the power supply.
What could be the reason for the lower-than-expected current reading?
How would you troubleshoot to resolve the issue?
These questions help students apply their knowledge of measuring instruments to real-world circuit analysis and troubleshooting scenarios.
Evaluation: Multiple Choice Questions
1
Which of the following instruments is used to measure voltage, resistance, and current in a circuit?
A) Tachometer
B) Volt-Ohm-Milliammeter (VOM)
C) Oscilloscope
D) Ampere Meter
2
What is the primary use of a tachometer?
A) To measure the electrical resistance in a circuit.
B) To measure the speed (RPM) of a rotating object.
C) To measure the voltage in an electrical circuit.
D) To display the waveform of a signal.
Evaluation: Multiple Choice Questions (Continued)
1
Which instrument is used to display the waveform of electrical signals over time?
A) Volt-Ohm-Milliammeter (VOM)
B) Ampere Meter
C) Tachometer
D) Oscilloscope
2
An ammeter is used to measure which of the following?
A) Speed of a rotating object
B) Electrical current in a circuit
C) Voltage across two points in a circuit
D) Frequency of electrical signals
Evaluation: Final Question
Question 5: Which of these instruments is commonly used in automotive applications to monitor engine speed (RPM)?
A) Ampere Meter
Used to measure electrical current flow in a circuit
B) Oscilloscope
Used to visualize and analyze electrical signal waveforms
C) Tachometer
Used to measure rotational speed of an engine or shaft
D) Volt-Ohm-Milliammeter (VOM)
Used to measure voltage, resistance, and current
Answer Key
Question 1
B
Question 2
B
Question 3
D
Question 4
B
Question 5
C
The correct answer is C) Tachometer - the instrument specifically designed for measuring rotational speed.
Additional Resources
These resources provide additional visual references for understanding the proper use and application of various measuring instruments in electrical and mechanical systems.
References and Learning Resources
1
YouTube Videos
Analog multi meter parts and functions (Part 1)
Analog multimeter resistance reading Part 2
Analog multimeter AC & DC voltage reading Part 3
Analog multimeter DC current reading Part 4
How to Measure Current (Amperes) using Analog Multi-meter
How to use a multimeter like a Pro, the ultimate guide
2
Online Articles
Fluke: What is a digital multimeter?
Tameson: How to use a multimeter, types, components and more
wikiHow: How to Read a Multimeter
Circuit Globe: Volt-Ohm-Milli-Ammeter (VOM)