General Principles of Measurement

            Measurement is the process by which one can convert physical parameters in to meaningful numbers. The measurement of a given quantity is the result of comparison between the quantity to be measured, and a definite standard. The instruments which are used for such measurements are called measuring instruments.

            The necessary requirements for any measuring instruments are;

1)      With the introduction of the instrument in the circuit, the circuit, the circuit conditions should not be altered. Thus, the quantity to be measured should not get affected due to the instrument used.

2)      The power consumed by the instruments for their operation should be as small as possible.

Some important terms in ‘measurement’ are;

Instrument

            A device for finding the value, or magnitude of a quantity or variable.

Accuracy

            It is the nearness of the measured value towards the true value. ie, the measure of conformity to the true value.

Precision

            It refers to the degree of agreement within a group of measurements or instruments. ie,The measure of repeatability or reproducibility. Precision has two characteristics: conformity and the no. of significant figures to which measurements may be made.

Resolution

It is defined as the smallest change in input that can be detected by an instrument.

Sensitivity

            It is the ratio of output signal to a change of input.

                                                Or

It is the ratio of response of an instrument to a change in measured variable.

True value

            It is the average of the infinite no. of measurements, when the average deviation tends to become zero.

Error

            An error is the deviation from the true value of the measured variable.

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 Reference:- (i) U.A Bakshi, A.V Bakshi, K.A Bakshi, Electrical measurements,Page no:- 1

(ii) D.P Kothari, J.J Nagarth, Basic Electrical Engineering, Page no:- 610

(iii) A.K Sawhney, Electrical and Electronic Instrumentation and Measurements, page no:-1