Evaluating Flow Meter Measurement Errors and Uncertainties

Abstract: Evaluation of flow meter measurement error and uncertainty information is provided by excellent flow meter and flow meter manufacturers and quotation manufacturers. 1. Measurement error and correction of measurement results (1) Measurement error The difference between the measurement result of the flowmeter minus the true value of the measured value is called measurement error, or error for short. The measurement result is the result that people recognize, not related to the quantity itself, but also to the measurement process. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the article evaluating the measurement error and uncertainty of flowmeters. 1. Measurement error and correction of measurement results (1) Measurement error The difference between the measurement result of the flowmeter minus the true value of the measured value is called measurement error, or error for short. The measurement result is the result that people recognize, not related to the quantity itself, but also related to the measurement procedure, the measurement instrument, the measurement environment and the measurement personnel. The true value of the measurand is a value that is consistent with the definition of the measurand, it is the complete embodiment of the definition of the quantity, is a value that is completely consistent with the definition of a given specific quantity, and can only be achieved through perfect or flawless measurement. get. The truth value is inherently indeterminate. In practice, however, for a given purpose, it is not necessary to obtain a specific amount of“truth value”, but only with“truth value”close enough value. Such a value is a contractual truth value, which can be used in place of a truth value for a given purpose. For example: the value of a specific quantity obtained by calibration or verification, or the value measured by a measuring instrument with a higher accuracy level, or the value determined by the results of multiple measurements, can be used as the agreed true value of the quantity . The error of the measurement result is often composed of several components, which can be divided into two categories: random error and systematic error according to their characteristics, and the algebraic sum of each component is taken without exception. In other words, any error can be decomposed into the algebraic sum of systematic error and random error, which can be expressed by the following formula: error = measurement result - true value = (measurement result - population mean) + (population mean - true value) = random Error + systematic error The difference between the measurement result and the average of the results obtained by infinitely measuring the same measurand under repeatability conditions is called random error. Random errors are mostly derived from the change of the influence quantity. This change is unpredictable or random in time and space, and it will cause changes in the repeated observations of the measurand, so it is called“random effects”. It can be argued that it is this random effect that causes the dispersion in repeated observations. Under the condition of repeatability, the difference between the average value of the result obtained by infinitely many times of measurement of the same measurand and the true value of the measurand is called the systematic error. Since only a limited number of repeated measurements can be made, and the true value can only be replaced by a conventional value, the possible determined systematic error is only its estimated value with a certain uncertainty. The systematic error probably originates from the influence quantity. If its influence on the measurement result has been identified, it can be expressed quantitatively, so it is called“system effect”. If the magnitude of this effect is significant, it can be compensated by an estimated correction. (2) Correction of measurement results The measurement results that have not been corrected for the systematic errors are called uncorrected results. When only a single indication is obtained by the measuring instrument, the indication is usually the uncorrected result; and when several indications are obtained, the uncorrected result is usually obtained from the arithmetic mean of these indications. For example: use a ruler to measure the diameter of a cylinder, and the indication value obtained from a single observation is 14.7mm, then the measured value is an uncorrected result. If 10 measurements are made, and the obtained indications are 14.9, 14.6, 14.8, 14.6, 14.9, 14.7, 14.7, 14.8, 14.9, 14.8 (mm), then the uncorrected result of the measurement column is its arithmetic mean, i.e. (14.9+14.6+…+14.8)/10=14.77≈14.8(mm). The measurement result after correcting the systematic error is called the corrected result. The value that is added algebraically to the uncorrected measurement to compensate for its systematic error is called the correction value. In the above example, if the ruler is calibrated by a gauge block and its correction value is -0.1mm, the corrected result of a single measurement is (14.7-0.1)mm=14.6mm; and the corrected result of 10 measurements is (14.8-0.1)mm=14.7mm. The correction value is equal to the negative systematic error, that is to say, adding a correction value is like deducting a systematic error, and its effect is the same. That is: true value = measurement result + correction value = measurement result - error It should be emphasized that: the systematic error can be estimated and compensated with an appropriate correction value, but this compensation is incomplete, that is, the correction value itself Contains uncertainty. When the measurement result is added to the correction value in the form of algebraic sum, the absolute value of the systematic error will be smaller than that before correction, but it cannot be zero, that is, the correction value can only compensate the systematic error to a limited extent. 2. Measurement uncertainty (1) Basic concept The purpose of measurement is to determine the measured value. The quality (quality) of the measurement results is the most important basis for measuring the reliability of the measurement results. Measurement uncertainty is a quantitative representation of the quality of measurement results, and the availability of measurement results largely depends on the size of its uncertainty.

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