Electrical Instruments 220

An overview of the various meters used in electrical maintenance. Basic principles, proper usage, and safety procedures are discussed.

Class Details

Class Name:
Electrical Instruments 220
An overview of the various meters used in electrical maintenance. Basic principles, proper usage, and safety procedures are discussed.
Number of Lessons:
Additional Language:
Related 2.0 Class:
Electrical Instruments 251

Class Outline

  • Objectives
  • The Importance of Electrical Instruments
  • Basic Principles and Instruments
  • Ohm’s Law Applications
  • Ammeter
  • Voltmeter
  • Ohmmeter
  • Multimeter (VOM)
  • Digital vs. Analog
  • Direct Current vs. Alternating Current
  • Wattmeter
  • Watt-Hour Meter
  • Other Specialized Meters
  • Common Safety Practices
  • Standards and Organizations
  • Summary


  • Describe various meters and their uses.
  • Explain the science behind basic electrical meters.
  • Explain the relationship between Ohm’s Law and electrical meters.
  • Describe the ammeter.
  • Describe the voltmeter.
  • Describe the ohmmeter.
  • Describe the multimeter.
  • Contrast new electrical meter technology with older systems.
  • Distinguish between DC and AC when meter readings.
  • Describe the wattmeter.
  • Describe the watt-hour meter.
  • Identify less common electrical meters.
  • Describe common safety practices for using electrical meters.
  • List the various organizations that set electrical industry standards.


  • MSSC Maintenance Awareness


Vocabulary Term Definition
ammeter A device used to measure current. An ammeter is connected in series to a circuit.
analog A mode of display using a scale and pointer. Analog meters allow interpolation and give a sense of quantity relative to other possible values.
cathode-ray tube An analog display device that uses a vacuum tube to generate images on a layer of phosphors driven by an electron beam.
current The flow of electricity. Current is measured in amps.
D'Arsonval movement An action caused by electromagnetic deflection, using a coil of wire and a magnetized field. When current passes through the coil, a needle is deflected.
decibel A unit used to convey the intensity of sound, abbreviated as dB.
decibel meter A device used to measure the intensity of sound. Many DMMs have a decibel meter function.
diode A two-terminal semiconductor device that allows current to flow through it in only one direction. A diode has a low resistance to electrical current in one direction and a high resistance in the other direction.
directly proportional A relationship where a number increases or decreases together with another number at the same ratio. Directly proportional is the opposite of inversely proportional.
DMM The abbreviation for a digital multimeter.
dynamometer movement An action using two stationary coils to measure power output. One coil is energized by voltage, the other by amperage, producing deflection.
efficiency A measure of the energy output of a system versus the total energy supplied to it.
electromagnet A magnet which is charged by a current-carrying coil wound around it. Electromagnets can produce much larger magnetic field than permanent magnets.
electromagnetic deflection The ability of an electrical current to displace a magnetic field. Electromagnetic deflection reacts to and is able to measure the magnitude or intensity of a field.
energy The ability to do work. Energy is measured in kWh and expressed as the product of power and time.
full scale deflection Moving the indicator all the way up without hitting the stop pin. The more sensitive the instrument, the less input it takes to reach full scale deflection.
galvanism An effect whereby electrical current causes mechanical motion. Galvanism reacts to polarity and accurately measures magnetic flux directionally.
galvanometer A basic device for measuring electric current by means of a mechanical motion derived from electromagnetic forces produced by the current.
International Electrotechnical Commission An organization that provides conformity assessment for government, business, and society for all electrical, electronic and related technologies.
interpolation Estimating the value of a quantity from known values on either side of it. Users of analog meters often must interpolate data on the readout.
kilowatt-hour meter The more common range of a watt-hour meter. Because energy is usually measured over an extended period of time, the use of power is expressed in kilowatts.
leads The red and black conductive wires attached to meters and connected to circuits.
lockout/tagout A method of protecting employees from accidental machine startup through proper locking and labeling of machines that are undergoing maintenance.
multimeter A device that combines the functions of an ammeter, voltmeter, and ohmmeter. A multimeter is the most versatile and common meter used today.
multirange A meter able to measure wide ranges using fixed internal series resistances. A dial on the meter makes it easy to switch to the different ranges.
National Electrical Code The minimum standard for safe electrical installations. The NEC is adopted in some form as law in all 50 states.
National Electrical Manufacturers Association An organization that defines a product, process, or procedure with reference to safety, performance, and testing.
National Fire Protection Association The organization that produces the National Electric Code. The NFPA outlines the minimum safety requirements for any electrical installation.
National Institute of Standards and Technology A federal agency that promotes innovation and industrial competitiveness by developing better standards and technology.
Ohm's Law The universal truth stating that it takes one volt to push one amp through one ohm.
ohmmeter A device used to measure resistance. A resistor must be removed from a circuit to attach an ohmmeter.
oscilloscope A device that produces a visual trace of voltage or current wave shapes, generally on a cathode ray tube.
perfect conductor A material that allows a completely free flow of electrons. A perfect conductor has zero resistance.
perfect insulator A material that does not allow any flow of electrons. A perfect insulator has infinite resistance.
polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow.
power The rate at which a device converts electrical energy into another form, such as heat or light. Power is measured in watts.
rectifier A device, such as a diode, that converts alternating current to direct current. Rectifiers allow meters to measure both DC and AC.
resistance The opposition to current flow. Resistance is measured in ohms.
resistor A device that restricts current flow and produces work, such as heat or light.
sensitivity The degree of response of an instrument to an incoming signal. A more sensitive meter can make more exact measurements.
shunt A low-resistance connection between two points in an electric circuit that forms an alternative path for a portion of the current. Shunts allow meters to produce accurate readings in a much wider range.
solenoid A cylindrical coil of wire that generates a force when an electrical current is applied.
solid state relay Circuitry that has replaced D'Arsonval movement in digital meters. SSR is faster and does not wear out.
voltage A measure of electrical pressure or potential known as electromotive force. Voltage is measured in volts.
voltmeter A device used to measure voltage. Voltmeters connect in parallel to a circuit.
VOM Abbreviation for volt, ohm, milliammeter, the most common setup of a multimeter. Because of this, multimeters are often known as VOMs.
watt-hour meter A device used to measure electrical energy.
wattmeter A device used to measure electrical power.
Wiggins solenoid meter A testing device that vibrates when a current is detected. Also called a "wiggy", it is small and durable, but may be replaced by more versatile and safer DMMs.