Electrical Measuring Instruments - An Introduction
What are the Electrical Measuring Instruments?
The instruments which are used to measure electrical quantities are known as electrical measuring instruments. Measurement is a process of comparison between a standard and unknown and knowing the result of the unknown in terms of standard. The measuring quantity can be voltage, current, power and energy etc.
Classification of Measuring Instruments
They are divided into two parts
- Absolute instruments
- Secondary instruments
Absolute Instruments
These
instruments give the quantity to be measured in terms of instrument constant
and its deflection. They do not require any comparison with any other standard
instruments. Due to a smaller number of moving mechanical parts, these
instruments are highly accurate. These instruments are rarely used because the measuring quantity varies with time.
Example- Tangent galvanometers,
Rayleigh current balance absolute electrometers etc.
Secondary Instruments
The deflection of these instruments gives the values of an electrical quantity to
be measured directly. These instruments are required to be calibrated by
comparison with either absolute instruments or secondary instruments. Which has
already been calibrated already. Due to large numbers of moving mechanical parts,
these instruments consume higher power in operation and are less accurate in the result.
Example - Ammeter, Voltmeter,
Wattmeter, Energy meter.
Types of Secondary Instruments
Analog instruments are further classified on the basis at the end of a measurement.
Deflecting Instruments - Deflecting instruments are those which indicate the end of measurement with deflection of pointer way from zero position. A finite amount of energy is consumed to produce this deflection, these instruments are relatively less accurate.
- Indicating Instruments
- Recording Instruments
- Integrating Instrument
Deflecting instruments are further classified on the basis of type output.
Indicating Instruments
These are the instruments which indicate
the magnitude of an electrical quantity at the time when it is being measured.
The indication is given by the pointer moving over a dial.
Example- ordinary
ammeter, voltmeter, wattmeter, frequency meter etc.
Recording Instruments
These are the instruments which
record the variations in the electrical quantity over a definite period of
time with the help of a pen and ink system.
Integrating Instrument
These instruments give the
electrical output multiplied by time. Integrating instruments gives the sum of
total electrical parameters consumed by a circuit over a period of time.
Example - Ampere-hour meters and energy meters.
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