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DETERMINING MEASUREMENT ACCURACY

by Hristo Stefanov

Start ý Defining the Terms ý A Little Theory ý Sources of Error ý Error Budget ý Error Budget Example ý Offset and Gain Errors ý Sources and PDF

A LITTLE THEORY

Every measuring system consists of function blocks in which signal conversion takes place. These blocks can be generally called measuring converters, or simply converters. An amplifier, ADC, filters, and so on are such converters. In the ideal converter, the output variable Y is a function of the input variable X only:

Y = ý(X)

In any real converter, the transfer function differs from the ideal one because of the presence of sources that cause inaccuracy (error sources):

Y = ý_R(X, A₁ýA_n)

If you substitute zero for all sources A₁ýA_n, you obtain the transfer function of the ideal converter:

Y = ý_R(X, 0,ý0)

The absolute error in the real converter is given by:

Y_EER = ý_R(X, A1ýAn) ý ý_R(X, 0ý0) = DY

The total differential of the function ý_R is:

Consequently, for infinitesimal values of A₁ýA_n, you can write:

This equation provides the justification for representing the overall systematic error of the linear converter as the sum of error terms. Every term corresponds to one source of error. This approach is the foundation for the error budget method.

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