ISO 2715:2017 液体炭化水素—タービン流量計による体積測定 | ページ 6

3.1.1

accuracy

closeness of the agreement between the measured quantity value and a true quantity value of a measurand

Note 1 to entry: The concept “measurement accuracy” is not a quantity, and should not be given a numerical value. The quantitative expression of accuracy should be in terms of uncertainty. “Good accuracy” or “more accurate” implies small measurement error. Any given numerical value should be taken as indicative of this.

[SOURCE:ISO/IEC Guide 99:2007, 2.13, modified]

3.1.2

adjustment

set of operations carried out on a meter or measuring system so that it provides prescribed indications corresponding to given values of the quantity measured

Note 1 to entry: Adjustment can be of zero point, span, linearity or other factors affecting the performance of the meter.

Note 2 to entry: Adjustment should not be confused with calibration, which is a prerequisite for adjustment.

Note 3 to entry: After adjustment, a recalibration is usually required.

[SOURCE:ISO/IEC Guide 99:2007, 3.11]

3.1.3

calibration

set of operations that establish, under specified conditions, the relationship between quantities indicated by an instrument and the corresponding values realized by standards

Note 1 to entry: Calibration should not be confused with adjustment of a measuring system.

[SOURCE:ISO/IEC Guide 99:2007, 2.39, modified]

3.1.4

cavitation

phenomenon related to, and following, flashing (3.1.6) where vapour bubbles or voids form and subsequently collapse or implode

Note 1 to entry: Cavitation causes significant measurement error and also potentially causes damage to the pipe and meter through erosion.

3.1.5

error

measured value minus a reference value

Note 1 to entry: Relative error is error divided by a reference value. This can be expressed as a percentage.

[SOURCE:ISO/IEC Guide 99:2007, 2.16, modified]

3.1.6

flashing

phenomenon which occurs when the line pressure drops to, or below, the vapour pressure of the liquid, allowing gas to appear from solution or through a component phase change

Note 1 to entry: Vapour pressure of the fluid can reduce with increasing temperature.

Note 2 to entry: Flashing is often due to a local pressure drop caused by an increase in liquid velocity, and generally causes significant measurement error.

Note 3 to entry: The free gas produced will remain for a considerable distance downstream of the meter even if pressure recovers.

3.1.7

flow conditioner

flow straightener

device installed upstream of a turbine meter to reduce swirl and velocity profile distortions

3.1.8

K-factor

ratio of the number of pulses obtained from a meter, and the quantity passed through the meter

3.1.9

linearity

total range of deviation of the accuracy curve from a constant value across a specified measurement range

Note 1 to entry: The maximum deviation is based on the mean of derived values at any one flow point.

Note 2 to entry: The deviation is the largest, minus the smallest value of mean values at each flowrate.

Note 3 to entry: Relative linearity is the range of values divided by a specified value, e.g. the independent linearity, as defined in ISO 11631.

3.1.10

lubricity

liquid property which affects friction between moving surfaces

Note 1 to entry: Good lubricity allows the formation of a liquid film between surfaces, and thereby reduces friction. Poor lubricity ここで, little or no film is formed, can result in accelerated component wear.

3.1.11

meter factor

ratio of the quantity indicated by the reference standard and the quantity indicated by the meter

3.1.12

performance indicator

derived value which may be used to indicate the performance of the meter

3.1.13

proving

calibration with comparison to defined acceptance criteria

Note 1 to entry: Proving is a term used in the oil industry, and is similar to “verification”.

Note 2 to entry: Proving is a calibration, sometimes of limited measurement range, according to methods defined by standards, regulation or procedures providing a determination of the errors of a meter and showing (proving) it performs to defined acceptance criteria.

3.1.14

pulse interpolation

means of increasing the effective resolution of the pulses output from a meter by multiplying the pulse frequency or measuring the fraction of a pulse associated with the total collected across a time period

Note 1 to entry: The latter is the most common method through a double timing technique.

3.1.15

range

measuring range

set of values of flowrate for which the error of a measuring instrument (flowmeter) is intended to lie within specified limits

[SOURCE:ISO Guide 99:1993]

3.1.16

range

range of values

difference between the maximum and minimum values of a set of values

Note 1 to entry: This can be expressed as a half range (±) number. Relative range is normally expressed as a percentage of a specified value, e.g. mean, minimum, or other calculated value.

3.1.17

repeatability

a

closeness of agreement between indications or measured quantity values obtained by replicate measurements under specified conditions

Note 1 to entry: Specified conditions normally imply the same reference, same conditions, same operators and procedures, and that the data are obtained sequentially over a short period of time.

Note 2 to entry: Repeatability can be expressed as the range (difference between the maximum and minimum) values of error or K-factor. Alternatively, repeatability can be expressed as a function of the standard deviation of the values.

Note 3 to entry: Dividing repeatability by the mean gives the relative value which can be expressed as a percentage. Some standards suggest dividing by the minimum value.

[SOURCE:ISO/IEC Guide 99:2007, 2.21, modified]

3.1.18

slip

measure of the fluid which passes through the meter without being directly measured

3.1.18.1

dynamic slip

slip measured when the meter is rotating

3.1.18.2

static slip

slip measured when the meter is not rotating

3.1.19

standard conditions

conditions of temperature and pressure to which measurements of volume or density are referred to standardize the quantity

Note 1 to entry: These are the specified values of the conditions to which the measured quantity is converted.

Note 2 to entry: For the petroleum industry, these are usually 15 °C, 20 °C or 60 °F and 101,325 kPa.

Note 3 to entry: Quantities expressed at standard conditions are shown by prefixing the volume unit by “S”, e.g. 4 Sm³ or 700 kg/Sm³.

Note 4 to entry: Definition has been adapted from Energy Institute HM 0 and OIML R 117. Some other petroleum standards employ the term “base” conditions.

Note 5 to entry: In some other documents, “standard” conditions are described as “base” conditions and, incorrectly, as “reference” conditions. Reference conditions are conditions of use (influence quantities) prescribed for testing the performance of a measuring instrument.

[SOURCE:ISO Guide 99:1993]

3.1.20

swirl

condition where the liquid flowing through a pipeline rotates with an associated high tangential component of velocity relative to the axial component

3.1.21

uncertainty

non-negative parameter characterizing the dispersion of the quantity values attributed to a measurand based on the information used

Note 1 to entry: Uncertainty is normally expressed as a half width range along with the probability distribution with that range. It can be expressed as a value, or as a percentage of the perceived true value.

[SOURCE:ISO/IEC Guide 99:2007, 2.26, modified]

3.1.22

velocity profile distortion

deviation from a fully developed velocity profile within a pipeline