EN ISO 6817:1995

SLOVENSKI STANDARD
01-september-1997
Measurement of conductive liquid flow in closed conduits - Method using
electromagnetic flowmeters
Measurement of conductive liquid flow in closed conduits - Methods using
electromagnetic flow-meters (ISO 6817:1992)
Durchflußmessung von leitfähigen Flüssigkeiten in geschlossenen Leitungen - Verfahren
mit magnetisch-induktiven Durchflußmeßgeräten (ISO 6817:1992)
Mesure de débit d'un fluide conducteur dans les conduites fermées - Méthode par
débitmetres électromagnétiques (ISO 6817:1992)
Ta slovenski standard je istoveten z: EN ISO 6817:1995
ICS:
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL
STANDARD ”
First edition
1992-l 2-o 1
Measurement of conductive liquid flow in closed
conduits - Method using electromagnetic
flowmeters
Mew-e de d&bit d’un fluide conducteur dans les conduites ferm6es -
MHhode par d&itm&tres 6lectromagrGtiques
Reference number
IS0 6817:1992(E)
IS0 6817:1992(E)
Contents
Page
1 Scope .
.......................................................................
2 Normative references
....................................................................................
3 Definitions
......................................................................
4 Symbols and units
...........................................................
5 Theoretical requirements
Construction and principle of operation .
................................................
7 Installation design and practice
8 Equipment marking .
................................................ 12
9 Calibration and test conditions
................................................................
IO Uncertainty analysis
Annexes
. . . . . . . . . . . . . . . . . . . . . .
A Materials for construction of primary devices
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B Bibliography
0 IS0 1992
All rights reserved. No part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without
permission in writing from the publisher.
International Organization for Standardization
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Printed in Switzerland
t
ii
\
IS0 6817:1992(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. international organizations, govern-
mental and non-governmental, in liaison with ISO, also take part in the
work. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Inter-
national Standard requires approval by at least 75 % of the member
bodies casting a vote.
International Standard IS0 6817 was prepared by Technical Committee
ISO/TC 30, Measurement of fluid flow in closed conduits, Sub-Committee
SC 5, Electromagnetic flowmeters.
The first edition cancels and replaces ISO/TR 6817:1980, of which it
constitutes a technical revision.
Annexes A and B of this International Standard are for information only.

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INTERNATIONAL STANDARD IS0 6817:1992(E)
Measurement of conductive liquid flow in closed conduits -
Method using electromagnetic flowmeters
IS0 7066-2:1988, Assessment of uncertainty in the
1 Scope
calibration and use of flow measurement devices -
Part 2: Non-linear calibration relationships.
This International Standard describes the principle
and main design features of industrial electro-
IS0 9104:1991, Measurement of fluid flow in closed
magnetic flowmeters for the measurement of flow-
conduits - Methods of evaluating the performance
rate of a conductive liquid in a closed conduit
of electromagnetic now-meters for liquids. ’
running full. It covers their installation, operation,
performance and calibration.
This International Standard does not specify safety
requirements in relation to hazardous environ-
3 Definitions
mental usage of the meter, nor does it apply to the
measurement of magnetically permeable slurries,
For the purposes of this international Standard, the
liquid metals nor usage in medical applications.
definitions given in IS0 4006 and the following defi-
nitions apply. Many of these are extracted from
This International Standard covers flowmeter types
IS0 4006 for ease of reference.
in both a.c. and pulsed d.c. versions.
3.1 electromagnetic flowmeter: Flowmeter which
creates a magnetic field perpendicular to the flow,
so enabling the flow-rate to be deduced from the
2 Normative references
induced electromotive force (e.m.f.) produced by the
motion of a conducting liquid’) in the magnetic field.
The following standards contain provisions which,
The electromagnetic flowmeter consists of a primary
through reference in this text, constitute provisions
device and one or more secondary devices.
of this International Standard. At the time of publi-
cation, the editions indicated were valid. All stan-
3.1.1 primary device: Device containing the follow-
dards are subject to revision, and parties to
ing elements:
agreements based on this International Standard
are encouraged to investigate the possibility of ap-
- an electrically insulated meter tube through
plying the most recent editions of the standards in-
which the conductive liquid to be metered flows,
dicated below. Members of IEC and IS0 maintain
registers of currently valid International Standards.
- one or more pairs of electrodes, diametrically
opposed, across which the signal generated in
IS0 4006:1991, Measurement of fluid f7ow in closed
the liquid is measured,
conduits - Vocabulary and symbols.
- an electromagnet for producing a magnetic field
IS0 5168:1978, Measurement of fluid flow - Esti-
in the meter tube.
mation of uncertainty of a flow-rate measurement.
IS0 706601:1989, Assessment of uncertainty in the The primary device develops a signal proportional
calibration and use of flow measurement devices - to the flow-rate and in some cases the reference
Part I: Linear calibration relationships. signal.
1) In the present International Standard, for electromagnetic flowmeters, the more correct term “liquid” replaces the word
“fluid” (covering liquids and gases) of the general definition in IS0 4006. This usage also aligns with that in IS0 9104.
IS0 6817:1992(E)
3.1.2 secondary device: Equipment which contains defined reference conditions for a given value of the
the circuitry which extracts the flow signal from the reference signal.
electrode signal and converts it to a standard output
signal directly proportional to flow-rate. This equip-
3.9 full-scale flowrate: Flow-rate corresponding to
ment may be mounted on the primary device.
the maximum output signal.
3.10 cathodic protection: Electrochemical means
3.2 meter tube: Pipe section of the primary device
of preventing electrolytic corrosion of conduits.
through which the liquid to be measured flows; its
inner surface is usually electrically insulated.
3.11 reference conditions: Conditions for cali-
bration of a flowmeter in accordance with clause 8
3.3 meter electrodes: One or more pairs of contacts
of this International Standard.
by means of which the induced voltage is detected.
3.4 magnetic field: Magnetic flux, generated by the
electromagnet in the primary device, which passes
4 Symbols and units
through the meter tube and through the liquid.
The following symbols are used in this International
Standard.
3.5 electrode signal: Total potential difference be-
tween the electrodes, consisting of the flow signal
Symbol Quantity Units
and the signals not related to flow such as in-phase,
quadrature and common mode voltages.
B Magnetic flux density tesla (T)
D Inside diameter of meter metres (m)
3.51 flow signal: That part of the electrode signal
tube
which is proportional to the flow-rate and the mag-
K Calibration constant metres (m)
netic field strength and which is dependent on the
Distance between meas- metres (m)
L
geometry of the meter tube and the electrodes.
uring electrodes
u Mean axial liquid velocity metres per
second (m/s)
3.52 in-phase voltage: That part of the electrode
signal in phase with the flow signal but which does
V Flow signal (electromotive volts (V)
not vary with the flowrate. force)
k Constant (dimensionless)
NOTE 1 This definition applies only to primary devices
Volume flow-rate of the cubic metres
4v
with a.c.-energized electromagnets.
liquid
quadrature voltage: That part of the electrode
3.53
signal which is 90” out of phase with the flow signal
and which does not vary with the flow-rate.
5 Theoretical requirements
3.54 common mode voltage: Voltage which exists
equally between each electrode and a reference
potential.
5.1 General
3.6 reference signal: Signal, proportional to the
When a liquid moves in a magnetic field, voltages
magnetic flux created in the primary device, which
(e.m.f.s) are generated in accordance with
is compared in the secondary device with the flow
Faraday’s law (see figure 1). If the field is perpen-
signal.
dicular to an electrically-insulated pipe which con-
tains the moving liquid and if the electrical
conductivity of the liquid is not too low, a voltage
3.7 output signal: Output from the secondary de-
may be measured between fwo electrodes on the
vice which is a function of the flow-rate.
wall of the pipe. This voltage is proportional to the
magnetic flux density, the average velocity of the
3.8 calibration factor of the primary device: A liquid and the distance between the electrodes. Thus
number which enables the flow signal to be related the velocity and hence the flow-rate of the liquid may
to the volume flow-rate (or average velocity) under be measured.
IS0 6817:1992(E)
usually determined by wet calibration, as described
5.2 Basic equation
in clause 9 and in IS0 9104.
In accordance with Faraday’s law of induction, the
strength of the induced voltages is given by the
Construction and principle of operation
simplified expression as
V= kBL,U. . . .
(1)
6.1 General
The volume flow-rate in the case of a circular pipe
As indicated schematically in figures 1 and 2, a pipe
is
is so placed with respect to the magnetic field that
nD2 the path of the conductive liquid, flowing in the pipe,
--
-
u
. . .
4v (2)
is normal to the magnetic field. In accordance with
Faraday’s law, motion of the liquid through the
which combined with equation (1) gives
magnetic field induces an electromotive force in the
liquid in a path mutually normal to the field and the
. . .
direction of liquid motion. By placing electrodes in
insulated mountings or by using insulated elec-
trodes with capacitance-type coupling in the pipe in
or
a diametrical plane normal to the magnetic field, a
potential difference proportional to the flow velocity
is produced which can be processed by a secondary
device. Meters based on this principle are capable
Equation (4) may be interpreted in various ways to
of measuring flow in either direction through the
produce a calibration factor which in practice is meter tube.
Magnet Ic flux
/-
Electrodes
Electromo
Magnetic cdl
B Magnetic flux density
Inside diameter of meter tube
V Flow signal (electromotive force)
U Mean axial liquid velocity
Figure 1 - Principle of an electromagnetic flowmeter

IS0 6817:1992(E)
The electromagnetic flowmeter consists of a primary chosen to be compatible with the liquid to be me-
device through which the process liquid flows, and tered.
a secondary device which converts the low-level
Other specific designs are also available, for exam-
signal generated by the primary device into a
ple, a cast steel case with the coils insulated inside
standardized signal for suitable acceptance by in-
the case and liners fitted internally to this again.
dustrial instrumentation (see, for example, IEC 381).
Flanges are usually provided to connect the primary
The system produces an output signal proportional
device to the plant pipework, although flangeless
to volume flow-rate (or average velocity). Its appli-
meters are available in smaller sizes.
cation is generally limited only by the requirement
that the metered liquid shall be electrically
The coils producing the magnetic field may be en-
conductive and non-magnetic.
ergized from the normal single-phase supply, or
from some other supply. The coil assembly is either
The primary and the secondary devices can be
mounted externally or encapsulated within the pipe.
combined in a single assembly.
In the latter case, the pipe may be made of magnetic
material.
6.2 Primary devices
In industrial electromagnetic flowmeters, the coils in
The primary device of an electromagnetic flowmeter
the primary device can be either
consists of the coils, a yoke of ferromagnetic ma-
terial, the meter tube through which the liquid flows
- a.c. energized, or
and the
...