Test and measurement instruments

Knowing the fundamentals

Test and measurement instruments are used to measure various magnitudes in an electric circuit such as:

• Current (A)
• Voltage (V)
• Resistance (Ω)
• Frequency (Hz)
• Capacitance (F) Farads
• Temperature (°C or K)
• Continuity (buzzing sound)


Test and measurement instrument may include:

• Digital multimeter (DMM)
• Clamp meter
• Analogue multimeter
• Insulation tester
• Voltage tester
• Phase rotation
• Earth resistance
• Earth leakage circuit breaker (ELCB) /Polarity
• Loop impedance tester


Compliance to safety standards

Measuring instruments need to adhere to international safety standard. Underwriters Laboratories (UL), based in Canada are independent testing laboratory that tests products against international standards.

International measurement categories:

Category Level Description Example
IV Primary supply level Meausurement performed at the source of the low voltage installation


  • Electricity meters
  • Transformers
III Distribution level Measurement performed at building installation


  • Distribution boards
  • Circuit breakers
  • Bus bars
  • Junction boxes
II Local level Measurement on circuits directly connected to the low voltage installation


  • Household appliances
  • Portable tools
I Signal level Measurement of electronic


  • Printers
  • Faxes



Multimeters are available as either a digital (DMM) or analogue meter.

Digital multimeter

This type of meter gives the output reading in numbers and is used to measure:Digital Multimeter

  • AC/DC Voltage
  • Resistance (Ω)
  • AC/DC current (A)
  • Frequency (Hz)
  • Capacitance (f)
  • Temperature (°C or °F)

Other features may include:

  • Relative zero
  • Data hold
  • Peak hold
  • Max hold
  • Min hold
  • Diode test
  • Continuity (Audible)
  • Overload protection (6kV) transient protection
  • 5000 Counts
  • Nullification on leads
  • Bar graph

Multimeters can be either auto or manual ranging

Auto Range

The range to be measured is automatically selected by the unit manual ranging

Manual Range

The range selected manually using the selector switch prior to the measurement being taken











Clamp Meter

  • Also referred to as Tong tester or Current transformer (CT)
  • Additional features include:
    -    AC/DC voltage
    -    Resistance (continuity)
    -    Frequency
    -    Capacitance *temperature
  • No need to break line (clamp over)