Agilent Technologies 4294A Specifications download pdf (Page 10)

1-4. True, effective, and indicated values

A thorough understanding of true, effective, and indicated values of a component, as well as their

significance to component measurements, is essential before you proceed with making practical

measurements.

➣ A true value is the value of a circuit component (resistor, inductor or capacitor) that excludes

the defects of its parasitics. In many cases, the true value can be defined by a mathematical

relationship involving the component’s physical composition. In the real-world, true values are

only of academic interest (Figure 1-6 (a)).

➣ The effective value takes into consideration the effects of a component’s parasitics. The effec-

tive value is the algebraic sum of the circuit component’s real and reactive vectors; thus, it is

frequency dependent (Figure 1-6 (b)).

➣ The indicated value is the value obtained with and displayed by the measurement instrument;

it reflects the instrument’s inherent losses and inaccuracies. Indicated values always contain

errors when compared to true or effective values. They also vary intrinsically from one mea-

surement to another; their differences depend on a multitude of considerations. Comparing

how closely an indicated value agrees with the effective value under a defined set of measure-

ment conditions lets you judge the measurement’s quality (Figure 1-6 (c)).

The effective value is what we want to know, and the goal of measurement is to have the indicated

value to be as close as possible to the effective value.

Figure 1-6. True, effective, and indicated values

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Agilent Technologies 4294A Specifications Page 10