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 |
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III | Distribution level | Measurement performed at building installation |
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II | Local level | Measurement on circuits directly connected to the low voltage installation |
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I | Signal level | Measurement of electronic equipment |
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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:
- 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 |
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Manual Range |
The range selected manually using the selector switch prior to the measurement being taken |
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Clamp Meter
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