Electrical instruments measure the various electrical quantities like electrical power factors, power, voltage and current etc. All analog electrical instruments use the mechanical system for the measurement of various electrical quantities but as we know that the all mechanical system has some inertia, therefore, electrical instruments have a limited time response.
Absolute instruments are defined as the instruments that give turning in terms of physical constants and not measurable on a graduated scale.
1. The value of the electrical quantity to be measured is given by these instruments.
2. The quantity is measured in terms of constants and from the deflection of the instruments only.
3. Tangent galvanometer, Reyleigh current balance, and absolute electro-meter are some of the examples of absolute instruments.
Secondary Measuring Instruments instruments are established with the help of absolute instruments. Secondary instruments are calibrated by comparison with absolute instruments. These are more regularly used in the measurement of the quantities as compared to absolute instruments, as working with absolute instruments is time-consuming. Another way of categorizing the electrical measuring instruments depends on the way they produce the result of measurements.
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. The example of instruments is Ammeters, Voltmeters, and watt-meters.
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.
The total quantity of either electricity or electrical energy contribute 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.
The popular type of electrical measuring instrument because of its versatility. It works like an ammeter, ohmmeter and voltmeter for it can measure current, voltage as well as resistance. Similar to other electrical measuring instruments, multitester are available in analog and digital types.