Electrical Engineering ⇒ Topic : Types of Secondary Instruments

Types of Secondary Instruments

Secondary instruments may be classified according to their functions as (i) indicating instruments (ii) integrating instruments and (iii) recording instruments.

(1) Indicating instruments. Those instruments which directly indicate the value of the electrical quantity at the time when it is being measured are called indicating instruments e.g. ammeters, voltmeters and wattmeters. In such instruments, a pointer moving over a graduated scale directly gives the value of the electrical quantity being measured. For example, when an ammeter is connected in the circuit, the pointer of the meter directly indicates the value of current flowing in the circuit at that time

(2) Integrating instruments. Those instruments which measure the total quantity of electricity(in ampere-hours) or electrical energy (in watt-hours) in a given time are called integrating instruments e.g. ampere-hour meter and watt-hour meter. In such instruments, there are sets of dials and pointers which register the total quantity of electricity or electrical energy supplied to the load.

(3) Recording instruments. Those instruments which give a continuous record of the variations of the electrical quantity to be measured are called recording instruments. A recording instrument is merely an indicating instrument with a pen attached to its pointer. The pen rests lightly on a chart wrapped over a drum moving with a slow uniform speed. The motion of the drum is in a direction perpendicular to the direction of the pointer. The path traced out by the pen indicates the manner in which the quantity, being measured, has varied during the time of the record. Recording voltmeters are used in supply stations to record the voltage of the supply mains during the day. Recordingammeters are employed in supply stations for registering the current taken from the batteries.