What is a Measuring Instrument?
The device used for comparing the unknown quantity
with the unit of measurement or standard quantity
is called a Measuring Instrument.
An instrument may be defined as a machine or
system which is designed to maintain functional
relationship between prescribed properties of
physical variables & could include means of
communication to human observer.
Classification of Electrical instruments
Electrical instruments may be divided into two categories,
- Absolute instruments.
- Secondary instruments.
- Absolute instruments
gives the quantity to be
measured in term of instrument constant & its
- In Secondary instruments
the deflection gives the
magnitude of electrical quantity to be measured
directly. These instruments are required to be
calibrated by comparing with another standard
instrument before putting into use.
Classification of Secondary instruments
Secondary instruments can be classified into three
- Indicating instruments
- Recording instruments
- Integrating instruments
- Indicating Instruments
: It indicate the magnitude of an electrical quantity at the time when it is being
measured. The indications are given by a pointer moving over a graduated dial.
Fig. 1: Indicating Instrument.
- Recording Instruments
: The instruments which keep a continuous record of the variations of the magnitude of an electrical quantity to be observed over a defined period of time.
Fig. 2: Recording Instrument.
- Integrating Instruments
: The instruments which measure the total amount of either quantity of electricity or electrical energy supplied over a period of time. For example energy meters.
Fig. 3: Integrating Instrument.
Use of electrical instruments
The electrical instrument is used for
measuring electrical quantities likes current,
voltage, power, etc. The ammeter
are the examples of
the electrical measuring instrument. The
ammeter measures the current in amps;
voltmeter measures voltage and Wattmeter
are used for measuring the power.