Question

Difference between absolute and secondary instruments

Answer 1

There are two types of Electrical Measuring Instruments:

1. Absolute Instruments – these instruments give the values of the quantity that has to be measured in terms of physical constants and their deflection only. 

They do not need to be calibrated and do not need any comparison with other standard instruments.

Examples – Tangent Galvanometer, Absolute electrometer, and Raleigh current balance.

2. Secondary instruments – these are instruments whose output is measured to give the value of the quantity. The quantity to be measured is determined by the deflection value of these instruments.

These instruments need to be calibrated against an absolute instrument.

Examples – ammeter, voltmeter, ampere-hour meter, wattmeter etc.

Absolute instruments are used in laboratories as standardizing instruments, whereas secondary instruments are used in everyday work.

Answer 2

Absolute instrument:

The instrument which gives

the value of the quantity to be measured in terms of the constant of the instruments are called Absolute instrument. e.g., tangent galvanometer.

Secondary instrument:

The instruments which is used

measure electrical quantity in terms of deflection

are called secondary instrument. There instrument is

used in practical lab. There are classified as:

i) Indicating instruments: The instrument which in

dicate the magnitude of electrical quantity being mea

sured instantaneously are called indicating instrument.

In such instrument of pointer moves over the calibrated

scale to indicates the magnitude of electrical quantity

being measured. Ex: Ammeter, voltmeter, wattmeter.

(ii) Integrating instruments :The instrument which is

used to measure the total energy in a given period are

called integrating instrument. In such instruments the

product of time and an electrical quantity under mea

instrument for example; energy meter, Ampere power

meter.

(iii) Recording instruments : The instrument which

gives a continuous record of the variation of the magnitude of an electrical quantity to be measured over a definite period of time are called recording instrument.

e.g: CRO, E-meter etc.

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