The measurement error is defined as the difference between the measured value and the "true value". Measurement errors affect any measuring instrument and can be due to different causes. Those that can be predicted in some way, calculated, eliminated by calibrations and compensations, are called deterministic or systematic and are related to the accuracy of the measurements. Those that can not be predicted, because they depend on unknown causes, or stochastic, are called random and are related to the precision of the instrument.
Random error The laws or mechanisms that cause it due to its excessive complexity or its small influence on the final result are not known.
To know this type of errors we must first make a sampling of measurements. With the data of the successive measurements we can calculate its mean and sample standard deviation.
Systematic error They remain constant in absolute value and in the sign when measuring, a magnitude in the same conditions, and the laws that cause it are known.
To determine the systematic error of the measurement, a series of measurements must be made on a quantity Xo, the arithmetic mean of these measurements must be calculated and then the difference between the mean and the magnitude X0 must be found.
Systematic error = | media - X0 |
Although it is impossible to know all the causes of the error, it is convenient to know all the important causes and have an idea that allows us to evaluate the most frequent errors. The main causes that produce errors can be classified as:
Error due to the measuring instrument.
Error due to the operator.
Error due to environmental factors.
Error due to geometric tolerances of the piece itself.
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