Classification of Measuring Instruments
Measuring instruments may be broadly
classified as follows
1. Absolute instruments
2. Secondary instruments
(a) Indicating instruments
(b) Integrating instruments
(c) Recording instruments
Absolute and secondary instruments
Absolute instruments: “absolute
instruments are those which gives the value of the quantity to be measured, in
terms of the constants of the instruments and their deflection only”.
Such instruments do not require any
previous calibration or comparison.
Example: Tangent galvanometer (is a very
common example) and Rayleigh’s current balance instruments.
Uses: These instruments used as
standardizing instruments in laboratories.
Secondary instruments: “secondary instruments are
those in which the value of electrical quantity to be measured can be
determined from the deflection of the instruments”.
Such instruments are need to be
pre-calibrated by comparison with an absolute instrument. Without calibration,
the deflection of such instruments is meaningless.
Example: An ammeter, voltmeter, a glass
thermometer, and a pressure gauge instruments.
Uses: These instruments are generally used
in practical work.
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