ISO 20456:2017 閉じた導管内の流体の流れの測定 — 導電性液体用の電磁流量計の使用に関するガイダンス | ページ 6

3.1

electromagnetic flowmeter

flowmeter which creates a magnetic field perpendicular to the direction of flow, so enabling the flowrate to be deduced from the induced voltage, U_v, produced by the motion of a conducting fluid through the magnetic field

Note 1 to entry: The electromagnetic flowmeter consists of a sensor (3.2) and a transmitter (3.3) .

3.2

sensor

Note 1 to entry: The sensor produces a signal proportional to the flowrate and, in some cases, a reference signal (3.9) . See 6.2.

Note 2 to entry: For a sensor, the wording primary device or flowtube has previously been used.

Note 3 to entry: In some cases, further electrodes are used such as grounding electrodes, full pipe detection electrodes (empty pipe detection) (see 3.5).

3.3

transmitter

equipment which contains the circuitry which drives the field coils and extracts the flow signal

Note 1 to entry: This equipment may be mounted directly onto the sensor (3.2) or remotely, connected to the sensor by a cable.

Note 2 to entry: For a transmitter, the wording secondary device, converter or electronic unit has previously been used.

3.4

meter tube

pipe section of the sensor (3.2) through which the liquid flows, at least part of whose inner surface is electrically insulating

3.5

measuring electrodes

one or more pairs of electrical contacts or capacitor plates by means of which the induced voltage is detected

3.6

lower range value

lowest value of the measured variable that a device is set to measure

3.7

upper range value

highest value of the measured variable that a device is set to measure

3.8

span

difference between the upper and lower range values (3.6)

3.9

reference signal

signal which is proportional to the magnetic flux created in the sensor (3.2) and which is compared in the transmitter (3.3) with the flow signal

3.10

output signal

signal from the transmitter (3.3) which is a function of the flowrate

3.11

Reynolds number

dimensionless parameter expressing the ratio between the inertial and the viscous forces

Note 1 to entry: For closed pipe flow through an electromagnetic flowmeter (3.1) , Reynolds number should be based on the nominal diameter of the meter and corresponding mean velocity through a section of that size.

3.12

accuracy

closeness of the agreement between the result of a measurement and the (conventional) true value of the measurement

Note 1 to entry: The quantitative expression of accuracy should be in terms of uncertainty (see Annex E).

Note 2 to entry: The use of the term precision for accuracy should be avoided.

3.13

uncertainty

<of measurement> range within which the true value of the measured quantity can be expected to lie with a specified value and confidence level

Note 1 to entry: See Clause 11.

3.14

calibration factor

number, determined by liquid calibration, that enables the output signal (3.10) to be related to the volumetric flowrate

3.15

calibration

operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication

3.16

verification

<in-situ electronic verification> means of verifying that an electromagnetic flowmeter (3.1) is operating correctly, normally with a poorer uncertainty than under controlled laboratory conditions

3.17

calibration validation

number of runs (one or more) at flowrates between zero and the upper range value (3.7) in order to verify that the flowmeter does perform in the expected way and within the manufacturer's specification

3.18

measuring window

period of time during which the voltage representing the flow velocity is measured

3.19

ideal flow conditions

conditions that exist when a pipe is infinitely long and straight with no internal disturbances

Note 1 to entry: For electromagnetic flowmeters (3.1) , it may, in addition, also be assumed that the metering liquid has a viscosity and density similar to water. Under these conditions, the flow is axisymmetric and will be fully developed and turbulent at flowrates and pipe sizes most often found in industry.