Measurement of fluid flow in closed conduits—Flowrate measurement by means of vortex shedding flowmeters inserted in circular cross-section conduits running full
GB/T 25922-2023 Measurement of fluid flow in closed conduits - Flowrate measurement by means of vortex shedding flowmeters inserted in circular cross-section conduits running full
1 Scope
This document
a) describes the use of vortex shedding flow meters for liquids, gases, and steam, including a glossary and a set of engineering equations used for specifying performance,
b) provides technical information to assist the user in selecting, specifying and applying vortex shedding flowmeters, including influence effects,
c) describes typical construction and provides recommendations for inspection, certification, and material traceability,
d) describes availability of diagnostics associated with vortex shedding flowmeters,
e) provides calibration guidance,
f) does not apply to insertion type vortex shedding flowmeters,
g) applies only to closed conduits running full,
h) applies only to fluid flow that is steady or varies only slowly with time, and
i) applies to fluids considered to be single-phase.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4006 Measurement of fluid flow in closed conduits - Vocabulary and symbols
ISO/IEC Guide 99:2007 (JCGM 200:2012) International vocabulary of metrology - Basic and general concepts and associated terms (VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4006 and ISO/IEC Guide 99:2007 (JCGM 200:2012) and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
——ISO Online browsing platform: available at http://www.iso.org/obp
——IEC Electropedia: available at http://www.electropedia.org/
3.1 Definitions specific to this vortex flowmeter standard
3.1.1
K-factor
ratio of the meter output in number of pulses to the corresponding total volume of fluid passing through the meter during a measured period
Note: The variations in the K-factor can be presented as a function of either the pipe Reynolds number or flowrate at a specific set of thermodynamic conditions. The mean K-factor is commonly used and is defined by the following formula:
3.1.2
linearity
constancy of the K-factor (3.1.1) over a specified range defined either by the pipe Reynolds number or flowrate
Note 1: The upper and lower limits of the linear range are specified by the manufacturer.
Note 2: See Figure 1.
3.1.3
cavitation
phenomenon following flashing, in which the pressure recovers above the vapour pressure and the vapour bubble collapses (implodes)
Note: Cavitation can result in measurement error as well as mechanical damage to the meter.
3.1.4
flashing
formation of vapour bubbles
Note: Flashing occurs when the pressure falls below the vapour pressure of the liquid.
3.2 Definitions related to measurement of fluid flow in closed conduits
3.2.1
pressure loss
irrecoverable pressure loss caused by the presence of a primary device in the conduit
3.2.2
Strouhal number
dimensionless parameter relating the vortex shedding frequency, f, generated by a characteristic dimension, l, to the fluid velocity, v, given by the following formula:
3.3 Definitions related to the vocabulary used in metrology
3.3.1
systematic measurement error; systematic error of measurement;
systematic error
component of measurement error that, in replicate measurements, remains constant or varies in a predictable manner
Note 1: A reference quantity value for a systematic measurement error is a true quantity value, or a measured quantity value of a measurement standard of negligible measurement uncertainty, or a conventional quantity value.
Note 2: Systematic measurement error, and its causes, can be known or unknown. A correction can be applied to compensate for a known systematic measurement error.
Note 3: Systematic measurement error equals measurement error minus random measurement error.
3.3.2
measurement uncertainty; uncertainty of measurement
uncertainty
non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used
Note 1: Measurement uncertainty includes components arising from systematic effects, such as components associated with corrections and the assigned quantity values of measurement standards, as well as the definitional uncertainty. Sometimes estimated systematic effects are not corrected for but, instead, associated measurement uncertainty components are incorporated.
Note 2: The parameter can be, for example, a standard deviation called standard measurement uncertainty (or a specified multiple of it), or the half-width of an interval, having a stated coverage probability.
Note 3: Measurement uncertainty comprises, in general, many components. Some of these can be evaluated by Type A evaluation of measurement uncertainty from the statistical distribution of the quantity values from a series of measurements and can be characterized by standard deviations. The other components, which can be evaluated by Type B evaluation of measurement uncertainty, can also be characterized by standard deviations, evaluated from probability density functions based on experience or other information.
Note 4: In general, for a given set of information, it is understood that the measurement uncertainty is associated with a stated quantity value attributed to the measurand. A modification of this value results in a modification of the associated uncertainty.
4 Symbols and subscripts
4.1 Symbols
