Industry characteristics of flow measurement and its requirements for instruments

Abstract: The information on the industry characteristics of flow measurement and its requirements for instruments is provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. 1 Terms of flow measurement 1.1 Terms and symbols for measurement of fluid flow in closed pipelines The terms and corresponding symbols used in this paper are in line with GB/T 17611-1998 'Terms and symbols for measurement of fluid flow in closed pipelines' (idt ISO 4006:1991 ), of which the following. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following are the industry characteristics of flow measurement and their requirements for the instrument. 1 Terms of flow measurement 1.1 Terms and symbols for measurement of fluid flow in closed pipelines The terms and corresponding symbols used in this paper are in line with GB/T 17611-1998 'Terms and symbols for measurement of fluid flow in closed pipelines' (idt ISO 4006:1991 ), in which the following terms and corresponding symbols have the following meanings. (1) Flow rate (flow~rate) The quotient of the amount of fluid flowing through a cross-section of a pipe and the time it takes for that amount to pass through the cross-section. ①Mass flow qm (mass flow~rate). The quantity of fluid is the flow rate expressed in terms of mass. ② volume flow qv (volume flow ~ rate). Amount of fluid The flow rate expressed in volume. (2) The average flow rate (mean flow~rate) is the average value of the flow rate over a period of time. (3) velocity distribution (velocity distribution) The distribution mode of the axial vector of the fluid velocity on the cross section of the pipe. ① Fully developed velocity distribution. A velocity profile that, once established, does not change from one cross-section of fluid flow to another. It is usually formed at the end of a long enough straight section of pipe. ②Regular velocity distribution. A velocity profile that closely approximates the fully developed velocity profile, facilitating accurate flow measurements. (4) Reynolds number Re (Reynolds number) is a dimensionless parameter representing the ratio of inertial force to viscous force. It is given by, i.e., where u——The average axial flow velocity through the specified area; ι——the characteristic size of the system that produces the flow; ν——The kinematic viscosity of the fluid. When specifying a Reynolds number, one should be specified as a reference feature size (eg diameter of pipe, diameter of orifice plate in differential pressure device, diameter of pitot tube measuring head, etc.). (5) The Strohal number Sr (Strohal number) is the dimensionless parameter of the vortex separation frequency f and the fluid velocity V phase produced by an object with characteristic size ι. It is given by (6) true value characterizes the strictly defined value under the conditions under which a quantity is studied when it is studied. The true value is an ideal value that can only be obtained by eliminating all causes of measurement error. (7) The (absolute) error of the measurement [(absolute) error of measurementJ minus the (conventional) true value of the measured value. ① This term is used equally for indications, uncorrected results and corrected results. ②The known part of the measurement error can be compensated by appropriate correction value. Errors in corrected results can only be characterized by uncertainty. ③'Absolute error' is signed and should not be confused with the absolute value of the error, which is the modulus of the error. (8) Spurious errors are errors that invalidate a measured value. Often these errors result from, for example, one or more of the significant digits being recorded incorrectly or malfunctioning of the meter. (9) Random error (random error) A component of the measurement error in which the same measurement value varies in an unpredictable manner during multiple measurements. Random errors are impossible to correct. (10) Systematic error A component of measurement error that remains unchanged or varies in a predictable manner for the same measurement value over multiple measurements. ①System errors and their causes can be known or unknown. ②The known part of the systematic error is not included in the uncertainty expected by the calibrated instrument (as an offset error, it should be deducted in advance). (11) Uncertainty U (uncertainty) represents an estimate that the true value of the measurand is within a certain range of magnitudes. The symbol e is sometimes used instead of U to denote uncertainty. Measurement uncertainty generally consists of multiple components, some of which can be estimated based on the statistical distribution of the measurement results column and can be characterized by standard deviation. Other components can only be estimated based on experience or other information. .①Random uncertainty Ur (random uncertainty) is the uncertainty component related to random error. Its effect on the average can be reduced by multiple measurements. ②The system uncertainty Us (systematic uncertainty) is the uncertainty component related to the system error. Its effect on the average cannot be reduced by multiple measurements. Figure 2.1 shows a description of terms related to error and uncertainty. (12) Accuracy (accuracy) The degree of agreement between the measured result and the (conventional) true value. Quantitative representations of precision should use uncertainty. Good accuracy means small random and systematic errors. Note that the term precision should be avoided in place of precision. (13) The quantity that is measured (measured). It can be a measured quantity or a quantity to be measured. (14) The maximum flow-rate corresponds to the flow value at the upper limit of the flow range. This is the highest flow value that requires the device to give information within a certain limit and a predetermined time interval, and the information error does not exceed the maximum allowable error. For water meters, the maximum flow is called overload flow.

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