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 equipment	Printers Faxes

Multimeter

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)