Intruduction ot Electical Measuring Instruments


Introduction to Electrical Measuring Instruments

The instruments, which are used to measure electrical quantity such as current, voltage, power, energy, frequency, power factor etc. are called Electrical Measuring Instruments. These instruments are generally named after the electrical quantity to be measured. Thus the instruments which measure current voltage, power, energy and frequency are known as ammeter voltmeter, wattmeter, energy meter and frequency meterrespectively.
The accuracy, convenience and reliability of electrical instruments are mainly responsible for the wide spread use of electrical methods of measurements.
The various types of indicating instruments along with their suitability for the type of measurements, type of control, type of damping, special features and applications are given in the below table

S.No
Type of Instrument
Suitability of measurements
Type of control
Type of Damping
1
Moving iron
DC or AC measurements (current & voltage)
Spring or gravity control
Air friction
2
Moving coil
(1) Permanent magnet type

(2) Dynamometer
C measurements (current &voltage only),
DC or AC measurements (current, voltage & power)
Spring


Spring
Eddy current


Air friction
3
Thermal
(1) Hot wire


(2) Thermo couple

DC or AC measurements (current, Voltage)
DC or AC measurements (current and voltage

Spring


Spring

Eddy current


Eddy current
4
Electrostatic
DC&AC (voltage and current)
Gravity or spring
Air friction
5
Induction
AC measurements only (current, voltage, power and energy)
Spring
Eddy current
6
Rectifier
DC or AC (current and voltage)
Spring
Eddy current



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