Types of Electrical Instruments:

Types of Electrical Measuring Instruments:

Electrical Instruments are basically classified into two types namely:

1. Absolute Instruments
2. Secondary Instruments

Absolute Instruments:
Definition:
Absolute instruments are defined as the instruments that give deflections in terms of physical constants and not measurable on a graduated scale.

• The value of the electrical quantity to be measured are given by these instruments.
• The quantity are measured in terms of constants and from the deflection of the instruments only.
• Tangent galvanometer, Reyleigh current balance and absolute electrometer are some of the examples of absolute instruments.

Secondary Instruments:
Definition:
They are defined as the instruments that give a ready measure of the quantities with the help of graduated scales.

• The value of the electrical quantity to be measured is determined from the deflection of these instruments.
• With an absolute instrument these instruments are calibrated. ie, the secondary instruments are compared with known standards or absolute instruments.
• All the electrical measuring instruments belong to this category.

There are three categories of secondary instruments.
1. Indicating instruments
2. Recording instruments
3. Integrating instruments

1. Indicating Instruments:
The value of the electrical quantity is indicated by these instruments at the time when it is being measured. Pointers moving over the scale give the indication.
Ammeters, Voltmeters and wattmeters are the examples of these instruments.

2. Recording Instruments:
A continuous record of variations of the electrical quantity over a long period of time is given by these instruments. It has a moving system which carries an inked pen which rests tightly on a graph chart.
Graphic recorders and galvanometer recorders are the examples of these instruments.

3. Integrating instruments
The total amount of either electricity or electrical energy supplied over a period of time is measured by these instruments.
Ampere hour meters, watt-hour meters, energy meters are the few examples of these instruments.