SIST EN ISO 20456:2019

SLOVENSKI STANDARD
01-december-2019
Nadomešča:
SIST EN 29104:2001
SIST EN ISO 6817:1997
Merjenje pretoka fluida v zaprtih vodih - Navodilo za uporabo elektromagnetnih
pretočnih meril za prevodne tekočine (ISO 20456:2017)
Measurement of fluid flow in closed conduits - Guidance for the use of electromagnetic
flowmeters for conductive liquids (ISO 20456:2017)
Messung des Durchflusses in geschlossenen Leitungen - Richtlinie für den Einsatz von
elektromagnetischen Durchflussmessgeräten für konduktive Fluide (ISO 20456:2017)
Mesurage du débit des fluides dans les conduites fermées - Lignes directrices pour
l'utilisation des débitmètres électromagnétiques dans les liquides conducteurs (ISO
20456:2017)
Ta slovenski standard je istoveten z: EN ISO 20456:2019
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.

EN ISO 20456
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2019
EUROPÄISCHE NORM
ICS 17.120.10 Supersedes EN 29104:1993, EN ISO 6817:1995
English Version
Measurement of fluid flow in closed conduits - Guidance
for the use of electromagnetic flowmeters for conductive
liquids (ISO 20456:2017)
Mesurage du débit des fluides dans les conduites Messung des Durchflusses in geschlossenen Leitungen
fermées - Lignes directrices pour l'utilisation des - Richtlinie für den Einsatz von elektromagnetischen
débitmètres électromagnétiques dans les liquides Durchflussmessgeräten für konduktive Fluide (ISO
conducteurs (ISO 20456:2017) 20456:2017)
This European Standard was approved by CEN on 26 August 2019.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20456:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 20456:2017 has been prepared by Technical Committee ISO/TC 30 "Measurement of
fluid flow in closed conduits” of the International Organization for Standardization (ISO) and has been
taken over as EN ISO 20456:2019 by CCMC.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by April 2020, and conflicting national standards shall be
withdrawn at the latest by April 2020.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 29104:1993 and EN ISO 6817:1995.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 20456:2017 has been approved by CEN as EN ISO 20456:2019 without any modification.

INTERNATIONAL ISO
STANDARD 20456
First edition
2017-09
Measurement of fluid flow in closed
conduits — Guidance for the use
of electromagnetic flowmeters for
conductive liquids
Mesurage du débit des fluides dans les conduites fermées — Lignes
directrices pour l'utilisation des débitmètres électromagnétiques dans
les liquides conducteurs
Reference number
ISO 20456:2017(E)
©
ISO 2017
ISO 20456:2017(E)
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

ISO 20456:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 Theory and basic formulae . 4
6 Construction and principle of operation . 4
6.1 General . 4
6.2 Sensor . 5
6.3 Transmitter . 7
6.3.1 General. 7
6.3.2 Alternating magnetic field in the measuring system . 7
6.3.3 Measuring system with applied pulsed DC excitation (simplified model) . 7
6.3.4 Measuring system with applied AC excitation (simplified model) . 8
6.4 Flowmeter/Transmitter output . 9
7 Equipment marking . 9
7.1 Recommended data . 9
7.1.1 Sensor . 9
7.1.2 Transmitter .10
8 Installation design and practice .10
8.1 Sensor .10
8.1.1 Sizing .10
8.1.2 Mounting conditions .11
8.1.3 Potential equalization — General requirements.12
8.1.4 Electrical connections .13
8.1.5 Sensor mounting .13
8.1.6 Installation dimensions for flanged connections .14
8.2 Transmitter location .15
8.3 Operational considerations .16
8.3.1 General.16
8.3.2 Effect of the liquid conductivity .16
8.3.3 Reynolds number effect .16
8.3.4 Velocity profile effect.16
9 Flowmeter calibration, validation, and verification .16
9.1 Flowmeter calibration .16
9.2 Flowmeter verification (in-situ electronic verification) . 16
10 Evaluation of flowmeter performance .17
10.1 General .17
10.2 Applications within the scope of other standards.17
11 Uncertainty analysis .17
Annex A (informative) Materials for construction of sensors .19
Annex B (informative) Practical considerations for measuring system with AC and DC excitation 22
Annex C (informative) Cathodic protection .23
Annex D (informative) Conversion of nominal diameters from metric to US units .24
Annex E (informative) Manufacturers' accuracy specifications.25
Bibliography .29
ISO 20456:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO 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, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed
conduits, Subcommittee SC 5, Velocity and mass methods.
This first edition of ISO 20456 cancels and replaces ISO 6817:1992, ISO 9104:1991 and ISO 13359:1998,
which has been technically revised.
iv © ISO 2017 – All rights reserved

ISO 20456:2017(E)
Introduction
Clauses 3 to 7 cover the definitions, symbols and basic theory of electromagnetic flowmeters. This
document does not cover insertion type meters, partially filled meters or meters for non-conductive
and highly conductive fluids.
Clause 8 covers installation types and practice, the different types of meter construction, transmitters, lay
lengths and sizing, in order to achieve the best performance of the electromagnetic flowmeter in the field.
Clauses 9 to 11 cover some methods of calibration, verification, evaluation, and uncertainty analysis,
which can be useful for users or independent testing establishments to verify manufacturer’s relative
performance and to demonstrate suitability of application
The tests specified in this document are not necessarily sufficient for instruments specifically designed
for unusually difficult duties. Conversely, a restricted series of tests may be suitable for instruments
designed to perform within a limited range of conditions.
This document is for users and manufacturers.
INTERNATIONAL STANDARD ISO 20456:2017(E)
Measurement of fluid flow in closed conduits —
Guidance for the use of electromagnetic flowmeters for
conductive liquids
1 Scope
This document applies to industrial electromagnetic flowmeters used for the measurement of flowrate
of a conductive liquid in a closed conduit running full. It covers flowmeter types utilizing both
alternating current (AC) and pulsed direct current (DC) circuits to drive the field coils and meters
running from a mains power supply and those operating from batteries or other sources of power.
This document is not applicable to insertion-type flowmeters or electromagnetic flowmeters designed
to work in open channels or pipes running partially full, nor does it apply to the measurement of
magnetically permeable slurries or liquid metal applications.
This document does not specify safety requirements in relation to hazardous environmental usage of
the flowmeter.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
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 , produced by the motion of a conducting fluid
v
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
device containing at least the following elements:
— an electrically insulating meter tube through which the conductive fluid to be measured flows;
— one pair of electrodes across which the signal generated in the fluid is measured;
— an electromagnet for producing a magnetic field in the meter tube (3.4)
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.
ISO 20456:2017(E)
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.
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ISO 20456:2017(E)
3.13
uncertainty
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
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.
4 Symbols
Symbol Quantity Units (SI)

magnetic field strength
Tesla (T)
B
mean magnetic field strength
Tesla (T)
B
a
d inside diameter of meter tube metres (m)

electric field strength volt per metre (V/m)
E
U electrochemical voltage volt (V)
c
U transformer voltage volt (V)
t
U velocity related voltage volt (V)
v
F Lorentz force newton (N)
Lorentz
k constant dimensionless (—)
k constant dimensionless (—)
ISO 20456:2017(E)
Symbol Quantity Units (SI)
L distance between measuring electrodes metres (m)
e
q volumetric flowrate of the liquid cubic meters per second (m /s)
V
mean axial liquid velocity
metres per second (m/s)
v
Nabla or Del operator
dimensionless (—)
∇
a
See Annex D for a conversion table of nominal diameters from metric to US units.
5 Theory and basic formulae
When a conductive liquid moves through a magnetic field, voltage(s), U , are generated in accordance
v
with Faraday’s law (see Formula 2). The strength of the induced voltages is given by the simplified
expression shown in Formula (1):
 

Fq=+Ev×B =0 (1)
()
Lorentz
 

Ev=− ×=BU∇ ;
()
v


∇ Uv=− ×B
()
v
Spatial integration of Formula (1) results in Formula (2):
Uk= BL v (2)
v 1e
The volume flowrate in the case of a circular pipe is given in Formula (3):
πd
q= v (3)
Which, combined with Formula (2), gives Formula (4):
U
πd  
v
q= (4)
 
4kL
B
 
1 e
Or Formula (5):
qk= U (5)
2 v
Formula (5) may be interpreted in various ways to produce a calibration factor which in practice is
usually determined by wet calibration, as described in 9.1.
6 Construction and principle of operation
6.1 General
As indicated schematically in Figure 1, the magnetic field is so placed with respect to a lined meter
tube that the path of the conductive liquid, flowing in the meter tube, is normal to the magnetic field.
In accordance with Faraday’s law, motion of the liquid through the magnetic field induces a voltage,
U , in the liquid in a path mutually normal both to the field and the direction of liquid motion. By
v
placing electrodes which contact the liquid in insulated mountings or by using insulated electrodes
with capacitance-type coupling in the meter tube in a diametrical plane normal to the magnetic field, a
4 © ISO 2017 – All rights reserved

ISO 20456:2017(E)
voltage proportional to the flow velocity is produced which can be processed by a transmitter. Meters
based on this principle are capable of measuring flow in either direction through the meter tube.
Key
1 coil system
2 lined meter tube
3 measuring electrodes
B magnetic flux density
L distance between measuring electrodes
e
U flow signal (velocity related voltage)
v
mean axial liquid velocity
v
Figure 1 — Principle of Faraday's law
The electromagnetic flowmeter consists of a sensor through which the process liquid flows and
a transmitter which converts the flow signal generated by the sensor into a standardized signal for
suitable acceptance by industrial instrumentation (see, for example, IEC 60381-1 and IEC 60381-2).
The system produces an output signal proportional to volume flowrate (or average velocity). Its
application is generally limited only by the requirement that the metered liquid shall be electrically
conductive.
The sensor and transmitter can be separate, linked by one or more electrical cables, or integrated with
the transmitter directly joined to the sensor.
6.2 Sensor
Figure 2 shows an exploded drawing of an industrial version of a sensor with an integrated transmitter.
The principal components of the sensor are as follows.
a) The meter tube is the pipe section of the sensor through which the liquid flows. For a meter
with field coils mounted outside the meter tube, this would be constructed from a non-magnetic
material. On a design where the field coils are inside the meter tube, it may be made of a magnetic
material.
b) An insulating liner which electrically insulates the measuring electrodes from the meter tube
preventing the induced U from short circuiting through the meter tube. The liner may be concentric
v
with the pipe or be profiled to provide a specific cross-section at the plane of the measuring
electrodes; if the meter tube is non-conductive, then a liner is not mandatory.
ISO 20456:2017(E)
c) The field coils produce the magnetic field. The most common configuration is to have two field coils
mounted diametrically opposite to each other, though single field coil designs are available. Field
coils may be mounted on the outside of the meter tube or within the meter tube isolated from the
fluid. The field coils can be either:
— excited by sinusoidal alternating current (AC), as described in 6.3.4, or
— excited by direct current. In this case, it is usual to use a pulsed direct current (DC) as described
further in 6.3.3;
d) The measuring electrodes which detect the induced U . These normally comprise two metallic
v
contacts diametrically opposite to each other standing slightly out from the liner which are in
direct contact with the fluid. In some designs for harsh applications, capacitive electrodes may be
used which are not in direct contact with the fluid.
The sensor may also contain a reference or ground electrode to provide a reference value for the
measured U , and/or an empty pipe detection electrode which triggers an alarm when not in contact
v
with the fluid.
The materials for the lining and for the electrodes shall be selected depending on the liquid to be
measured (see Annex A).
The sensor is usually connected to the piping by means of flanges; however, measuring devices
with flangeless versions and other process connections are also available. The process fluid shall be
electrically connected to the body of the flowmeter by means of a grounding electrode or electrically
conductive and unlined adjacent pipework or grounding (potential equalizing) rings; see 8.1.3.
A
B
Key
1 field coils
2 coil housing
3 lined meter tube
4 measuring electrodes
5 power supply
A transmitter
B sensor
Figure 2 — Elements of an industrial electromagnetic flowmeter
NOTE The sensor can have a non-circular cross-section.
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ISO 20456:2017(E)
6.3 Transmitter
6.3.1 General
The transmitter carries out the following functions:
a) provides the current to drive the field coils;
b) amplifies and processes the measuring electrode signal in order to derive a signal proportional to
the flowrate;
c) reduces various noise signals, e.g. fluid noise, electrical noise and common mode noise;
d) provides means of compensating for supply voltage and frequency variations where necessary;
e) provides the various outputs specified by the user or incorporated in the meter. These may include
a visual display and/or electronic outputs of the flowrate, alarm functions, totalised values and
diagnostics;
f) provides an interface for the user to configure the meter using buttons, touchpad or connections to
a PC or other device;
g) may provide an interface to a network.
Instruments may include additional circuitry to perform self-verification.
The transmitter may be mounted directly onto the sensor or remotely, connected to the sensor by a cable.
6.3.2 Alternating magnetic field in the measuring system
Electromagnetic flowmeters use an alternating magnetic field to avoid any voltages which may interfere
with the measurement of flow.
In addition to the flow related voltage, U , described in Clause 5, two other source voltages exist in
v
electromagnetic flowmeters. These are the electrochemical voltage, U , and the voltage created by
c
changes in the magnetic field, the transformer voltage, U . Both of these voltages may have a similar or
t
larger magnitude than U .
v
Further details may be found in Annex B.
6.3.3 Measuring system with applied pulsed DC excitation (simplified model)
In measuring systems with applied pulsed DC excitation, the magnetic field polarity is alternately
reversed. During each magnetic field polarity cycle, the electrode voltage is measured once the
magnetic field is considered to be constant. This period is called the measuring window (see Figure 3).
This measured voltage is a sum of both U and U .
c v
The difference between minimum and maximum value of the measured voltage, U , is proportional to
v
the flow velocity in the meter tube (see Figure 3).
ISO 20456:2017(E)
Key
measuring window
Figure 3 — Principle of pulsed DC system (simplified model)
6.3.4 Measuring system with applied AC excitation (simplified model)
In AC excitation, line voltage (typically 115 V or 230 V at 50 Hz or 60 Hz) is applied directly to the field
coils or is supplied by the transmitter. This voltage generates a magnetic field in the sensor that varies
in strength with the amplitude of the applied voltage. The variation follows the pattern of a sine wave
(see Figure 4). This means that the flow signal, U , will also be a sine wave. The peak to peak value of the
v
sine wave, U , will be proportional to the flow velocity.
v
8 © ISO 2017 – All rights reserved

ISO 20456:2017(E)
Key
measuring window
Figure 4 — Principle of AC excitation systems (simplified model)
6.4 Flowmeter/Transmitter output
The system output can be one or more of the following:
a) analogue direct current in accordance with IEC 60381-1;
b) analogue direct voltage in accordance with IEC 60381-2;
c) a frequency data output in the form of scaled or un-scaled pulses;
d) alarm output(s);
e) digital (e.g. communication buses);
f) wireless;
g) display.
NOTE Electromagnetic flowmeters are available as 2-wire and 4-wire systems.
7 Equipment marking
7.1 Recommended data
7.1.1 Sensor
The following data should be displayed either on the sensor or on a name plate:
a) instrument manufacturer;
ISO 20456:2017(E)
b) serial number;
c) nominal diameter;
d) maximum process temperature;
e) rated ambient temperature range;
f) maximum process pressure;
g) instrument classification (e.g. degree of protection, hazardous area classification);
h) model number.
NOTE 1 Rated ambient temperature range can be omitted if it is the same as the rated process temperature
range.
NOTE 2 Additional labelling requirements can be required for specific applications or to meet national
regulations (e.g. Ex approvals).
7.1.2 Transmitter
The following data should be displayed on a name plate:
a) instrument manufacturer;
b) serial number;
c) voltage, frequency, and power requirements;
d) instrument classification (e.g. degree of protection, hazardous area classification);
e) rated ambient temperature range;
f) model number.
NOTE Additional labelling requirements can be required for specific applications or to meet national
regulations (e.g. Ex approvals).
8 Installation design and practice
8.1 Sensor
8.1.1 Sizing
Usually, the sensor process connection size will be the same as that of the adjacent pipework. However,
care should be taken if the optimum performance is desired. Points to be considered are, for example:
— pipe size;
— pipe connection;
— flowrates;
— minimum and maximum flow to be measured;
— pressure loss.
The manufacturer's specifications, such as minimum span, velocity, abrasive fluid, low flow conditions
etc., should be followed. Typically, the measurement uncertainty of electromagnetic flowmeter will
be lowest above 1 m/s and below 1 m/s, the uncertainty will tend to increase. Although there is no
10 © ISO 2017 – All rights reserved

ISO 20456:2017(E)
theoretical maximum flowrate for an electromagnetic flowmeter, in practice, meters are sized such
that the maximum velocity does not exceed 10 m/s under normal operational conditions.
NOTE If flowmeter size is different from that of the adjacent pipework, then the effect of this discontinuity
can affect the flowmeter performance and pressure loss.
8.1.2 Mounting conditions
8.1.2.1 General
Provided the pipe remains full at all times, there is no theoretical restriction on the orientation in which
the sensor should be mounted. Where possible, if installing in a pipeline running vertically, ensure
the flow direction is upwards through the sensor to eliminate the possibility of annual flow errors. In
practice, the following conditions should be observed.
8.1.2.2 Effects of non-ideal flow conditions
Calibration laboratories strive to have flow conditions that are as close to ideal flow conditions.
Installing a flowmeter in conditions that are significantly different from ideal flow conditions, such as
placing the flowmeter closely downstream of an elbow or valve, may result in reduced performance.
Differences in the flowmeter design may have an effect on how much the performance is affected by
such non-ideal flow conditions.
8.1.2.3 Electrode position
In a horizontal pipe, since any gas bubbles will rise and collect at the top of the pipe, or sediment may
collect at the bottom of the pipe, the sensor should be mounted so that neither measuring electrode is
in these positions.
8.1.2.4 Zero-checking provision
If it is necessary to check the flowmeter zero in situ, then valves should be provided to stop the flow
through the device, leaving it filled with stationary liquid. When the flowmeter is equipped with an
automatically adjusting zero, this provision may not be necessary.
8.1.2.5 Multiphase flow through the sensor
8.1.2.5.1 Entrained solids
When solids are entrained in the liquid, care should be taken in the selection of the lining material and
electrode material (see Annex A). Where there is a possibility that material may settle in the sensor, it
should be mounted vertically or provision should be made to flush it through.
On spool piece devices, a ring to protect the leading edge of the electromagnetic flowmeter lining is
sometimes used. This ring shall be designed to ensure streamlined flow.
8.1.2.5.2 Entrained gases
Entrained gases cause measurement inaccuracies in direct relation to the volume percentage of gas
to liquid. An electromagnetic flowmeter measures velocity and computes the total volume flow by
multiplying the velocity by the cross sectional area. Precautions should be taken to reduce this effect by
increasing the liquid pressure, e.g. by locating the sensor on the high-pressure side of a restrictor such
as a control valve, or by eliminating the entrained gas.
NOTE High amounts of entrained gas can lead to a noisy measurement signal, or complete loss of the signal.
An automatic gas/air relief valve may be mounted at an appropriate distance before the sensor.
ISO 20456:2017(E)
8.1.2.6 Buried sensors
Where it is necessary to install sensors in underground pipework, they should be installed in appropriate
chambers. However, where it is necessary to backfill over the sensor, advice should be sought from the
manufacturer and appropriate steps taken to protect the sensor from corrosive ground conditions, soil
loading, and impact from excavators. For an installation below heavily stressed surfaces, e.g. streets, a
metal plate may need to be installed above the sensor. Connecting cables to the transmitter should be
run in a continuous length without joints which could be penetrated by groundwater.
8.1.2.7 Submerged sensors
Sensors installed in a location where they may be flooded or submerged should be rated to the
appropriate depth as expected in the application.
8.1.2.8 Access for maintenance and cleaning
Sensors installed in pipelines containing wastewater and some process waters with grease, fat or
entrained solids should be installed in such a way as to allow the bore to be cleaned. This may include
rodding points or tappings through which inspection and maintenance tools can be inserted. See
Figure 5.
Figure 5 — Design of typical installation diagram
8.1.3 Potential equalization — General requirements
In general, the flowmeter requires a connection to the metered liquid. This connection starts with one
of three things contacting the liquid, a metallic pipe, a grounding ring(s) (potential equalizing ring),
or a grounding electrode (see Figures 6 and 7). Usually, one of those is connected to the sensor body,
which is then connected to the correct terminal in the transmitter. In some cases, this connection to
the transmitter is not made via the sensor body. In the case of a cathodically protected pipeline, special
precautions shall be taken (see Annex C).
Some transmitters are constructed such that a connection to the metered liquid is not required. The
manufacturer's installation guidance should be followed.
NOTE The dotted connection in Figure 7 indicates that with non-metallic adjacent piping the dotted
connection can be omitted.
12 © ISO 2017 – All rights reserved
≥2 × DN
≥5 × DN
ISO 20456:2017(E)
Key
1 potential equalizing ring
2 non-coated metallic pipe work
Figure 6 — Installation in non-coated metallic pipe work
Key
1 equalizing ring
2 non-metallic or internally coated pipe work
Figure 7 — Installation in non-metallic or internally coated pipe work
8.1.4 Electrical connections
The manufacturer’s instructions shall be carefully followed for connections between the sensor and the
transmitter. Instructions in relation to electrical grounding of the flowmeter system shall be followed.
8.1.5 Sensor mounting
8.1.5.1 Full pipe requirements
The sensor shall be mounted in such a position that it will be completely filled with the liquid being
metered; otherwise, the measurement will not be within the manufacturer’s stated accuracy. Some
sensors include an additional electrode to detect when the meter is not running full and trigger an
alarm. Such systems are intended for horizontal pipe runs and the sensor would be installed with the
extra electrode in line with the crown of the pipe. Partially-filled sensor meters are used, for example,
in sewage applications, but these merit special consideration outside the scope of this document.
8.1.5.2 Mechanical connections
There are different varieties of fittings including flanges, wafer, hygienic couplings, clamps, threads and
welded connections. It is essential that the sensor is correctly aligned on the pipe axis.
ISO 20456:2017(E)
For flange connections:
— bolts should be tightened evenly and in moderation in order to avoid damage to the lining; the
manufacturer should state the maximum permissible torque;
— the manufacturer shall provide a reasonable clearance between the rear face of the flange and the
meter housing for installation and removal.
Care should be taken when handling the sensor; slings around the sensor or lifting lugs should be used.
Lifting by any means that could damage the liner, for example, hooks in the bore, shall not be used.
Under no circumstances shall the sensor be lifted using the cable which connects it to the transmitter.
Where gaskets are fitted between the meter and the pipe connection, care should be taken to ensure
that they are
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