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# Choosing the right measuring instrument

by：Sure     2021-08-16
1. The definition of measurement error The measurement error is the difference between the measurement result minus the measured true value, referred to as error. Because the true value (also known as the theoretical value) cannot be accurately obtained, in fact, the agreed true value is used, and the agreed true value needs to be characterized by the measurement uncertainty, so the measurement error cannot actually be obtained accurately. Measurement uncertainty: It indicates that the definition of measurement error is reasonably assigned to one of the measured values. Measurement error is the difference between the measurement result and the true value of the measured value, referred to as error. Because the true value (also known as the theoretical value) cannot be accurately obtained, in fact, the agreed true value is used, and the agreed true value needs to be characterized by the measurement uncertainty, so the measurement error cannot actually be obtained accurately. Uncertainty of measurement: It indicates that the dispersion of the measured value is reasonably assigned. It is related to the degree of people's understanding of the measured. It is an interval obtained through analysis and evaluation. Measurement error: It is the difference that indicates that the measurement result deviates from the true value. It exists objectively but people cannot be sure. For example: the measurement result may be very close to the true value (that is, the error is small), but due to insufficient knowledge, the value assigned by people falls within a larger area (that is, the measurement uncertainty is greater); it may actually be that the measurement error is relatively large. However, due to insufficient analysis and estimation, the uncertainty given is too small. Therefore, various influencing factors should be fully considered when evaluating the measurement uncertainty, and the necessary verification of the uncertainty evaluation should be carried out. 2. The error is divided into random error and system error. Error can be expressed as: error u003d measurement result-true value u003d random error + system error. Therefore, any error can be decomposed into system error and random error algebra and system error: The measurement error caused by the inherent error of the measurement tool (or measurement instrument), the measurement principle or the theoretical defect of the measurement method itself, the experimental operation and the constraints of the experimenter’s own psychological and physiological conditions are called system errors. The characteristic of systematic error is that under the same measurement conditions, the measurement result obtained by repeated measurement is always too large or too small, and the error value is constant or changes according to a certain rule. The method of reducing the system error can usually change the measurement tool or measurement method, and also consider the correction value of the measurement result. Random error: Random error is also called accidental error. Even in the ideal situation of completely eliminating system error, repeated measurement of the same measurement object will still produce measurement error due to the interference of various accidental and unpredictable uncertain factors. It is called random error. Random error is characterized by repeated measurements on the same measurement object, and the error of the measurement results obtained shows irregular fluctuations, which may be positive (the measurement result is too large) or negative (the measurement result is too small), and the error is absolute The value fluctuates irregularly. However, the distribution of errors obeys statistical laws and shows the following three characteristics: unimodality, that is, the error is smaller than the error is large; symmetry, that is, the probability of positive error and negative error is equal; boundedness, that is, the error is large The probability is almost zero.
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