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 meter
respectively.
The accuracy, convenience and reliability of electrical instruments are mainly responsible for the wide spread use of electrical methods of measurements.
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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