COMPARISON OF DIFFERENT TYPES OF ELECTRICAL MEASURING INSTRUMENTS

Electrical measuring instruments measure voltage, current, power, frequency, power factor, energy etc.

The classification of measuring instruments can be done in many ways. The broad classifications are,

• Absolute and Secondary instruments based on the methodology of measurement.
• Analog and Digital instruments based on the kind of output.
• Ammeter, Voltmeter, Wattmeter, Energy meter and Watthour meter based on the quantity of measurement.
• Indicating, Recording and Controlling instruments based on its function.
• Deflection type and Null type based on the indication of measurement.
• Magnetic effect, Chemical effect, Electrothermic effect, Electrostatic effect and Electromagnetic induction effect based on its working operation.

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Here, I present a detailed comparison of the main types of electrical measuring instruments based on its working principle.

TYPE OF INSTRUMENT	PERMANENT MAGNET MOVING COIL INSTRUMENT	MOVING IRON INSTRUMENT	ELECTRO DYNAMOMETER TYPE INSTRUMENT	THERMOCOUPLE TYPE INSTRUMENT	RECTIFIER TYPE INSTRUMENT	INDUCTION TYPE INSTRUMENT
SUITABILITY	DC	DC, AC	DC, AC	DC, AC	DC, AC	AC
QUANTITY MEASURED	Current & Voltage	Current & Voltage	Current, Voltage & Power	Current & Voltage	Current & Voltage	Current,  Voltage, Power & Energy
CONTROL TYPE	Spring control	Spring / Gravity control	Spring control	Spring control	Spring control	Spring control
DAMPING TYPE	Eddy current damping	Air friction damping	Air friction damping	Eddy current damping	Eddy current damping	Eddy current damping
EFFECT UTILISED	Magnetic effect	Magnetic effect	Magnetic effect	Electrothermic effect	Magnetic effect	Electromagnetic induction effect
READING SCALE PATTERN	Uniformly distributed	Non uniform scale (Scale is cramped at the beginning)	Non linear scale	Non uniform scale	Uniform Scale	Wide  non uniform scale. Deflection can be upto 300˚.
CURRENT VS DEFLECTION	θ α I	θ α I2	θ α I2	θ α I2	θ α I	θ α I2
KEY USE	Most accurate type of DC measurement.	Widely used in indicator type applications like on panels. The frequency of operation is 0 to 125 Hz.	Mainly used as wattmeter. Used as a standard meter for calibration and as transfer instrument.	Measures current and voltage at power frequencies up to 1000 MHz.	PMMMC is used in conjunction with rectifying devices for AC measurements for frequencies from 20 Hz to 20 kHz.	Mainly used for power and energy measurements in AC circuits.