Electrical Principles - Basic Instruments and Measurements

Chapter 2: Basic Instruments and Measurements

Topic Outcomes

  • Describe the correct procedure for using an ammeter, a voltmeter, and an ohmmeter.
  • Identify common symbols of electrical devices in electrical diagrams.

2.1 Types of Meters

  • Types of Meters:
    • Digital vs. Analog Meters
    • DC Power Supply
    • Function Generator
    • Oscilloscope
    • Voltmeters
    • Ammeter
    • Ohmmeter
    • Digital Multimeter
Digital Meters vs. Analog Meters
  • Digital meters provide a numerical display of the measured value.
  • Analog meters use a needle to indicate the measured value on a scale.
DC Power Supply
  • Definition: A direct current (DC) power supply provides current and voltage to power electronic circuits.
  • Has a specific symbol in circuit diagrams.
Function Generator
  • Definition: A function generator provides electronic signals for circuits.
  • Wave Generators:
    • Sinusoidal Generator: Represents a sine wave.
    • Pulse Generator: Represents a pulse or square wave.
    • Triangular Wave Generator: Represents a triangular wave.
Oscilloscope
  • Definition: The oscilloscope is used for observing and measuring voltage signals in a circuit.
Voltmeters
  • Definition: A voltmeter is used to measure voltage in a circuit.
  • Making a Voltage Measurement with a Voltmeter:
    • The voltmeter is connected in parallel with the component across which the voltage is to be measured.
Ammeter
  • Definition: An ammeter is used to measure current in a circuit.
  • Making a Current Measurement with an Ammeter:
    • The circuit must be broken, and the ammeter is inserted in series to measure the current.
Ohmmeter
  • Definition: An ohmmeter is used to measure resistance.
  • Making a Resistance Measurement with an Ohmmeter:
    • Connect the ohmmeter leads across the resistor to measure its resistance.
Digital Multimeter (DMM)
  • A digital multimeter measures voltage, current, or resistance, depending on the selected function.

Measuring Current

  • Steps to measure current using a multimeter:
    • Pull the wire out of the breadboard to open the circuit.
    • Connect the multimeter in series to measure the current.

Measuring Voltage and Current

  • Ammeter is used to measure current.
  • Voltmeter is used to measure voltage.

Important Note on Ammeter Usage

  • An ammeter will act as a short circuit if placed in parallel with a substantial voltage source.
  • This can cause a surge in current, potentially damaging the meter.

How to Use a Digital Multimeter (DMM)

Measuring Voltage
  1. Plug the probes into the meter (red to positive, black to negative).
  2. Turn the selector dial to DCV for direct current or ACV for alternating current.
  3. Choose the range setting based on the expected voltage (start high and adjust down).
  4. Turn the meter on.
  5. Hold the probes by the insulated handles and touch the red probe to the positive side and the black probe to the negative side of the circuit.
  6. Read the digital display.
Measuring Current
  1. Break the circuit in the desired location.
  2. Connect the red and black leads to the ammeter (black to negative, red to positive).
  3. Connect the ammeter in series with the circuit, ensuring correct polarity.
Measuring Resistance
  1. Turn the selector dial to the ohms range (Ω\Omega).
  2. Connect the test leads to the 'COM' and 'Ω\Omega' sockets.
  3. With nothing connected, the display will show an out-of-range indication.

2.2 Circuit Diagrams

  • Types of Circuit Diagrams:
    • Pictorial diagrams
    • Block diagrams
    • Schematic diagrams
Pictorial and Schematic Diagrams
  • Components:
    • Conductors (connected and not connected)
    • Cell and Battery (with schematic symbols)
    • Switches (SPST, SPDT, DPST, DPDT, Rotary type, NOPB, NCPB) - Showing Pictorial Representations and Schematic Symbols.
    • Fixed and Variable Resistors (with schematic symbols)
    • Voltmeter, Ammeter, milliammeter, microammeter, Ohmmeter (with symbols)
    • Fuses and Circuit Breakers (with symbols)
    • Fixed and Variable Inductors (air core and iron core, with symbols)
    • Fixed and Variable Capacitors (with symbols)
Block Diagram
  • Example 1: Power Distribution System
    • Shows the power source, power distribution components, and loads.
  • Example 2: TV Receiving System
    • Shows the TV antenna, receiver circuitry, picture tube, and speaker.

Summary

  • Power supplies provide current and voltage.
  • Voltmeters measure voltage.
  • Ammeters measure current.
  • Ohmmeters measure resistance.
  • Digital multimeters (DMM) measure voltage, current, and resistance.
  • Function generators provide electronic signals for circuits.
  • An oscilloscope is used for observing and measuring voltages in a circuit.
  • Circuit diagrams can be represented in three ways: pictorial, block, and schematic diagrams.