Measurement of conductive liquid flow in closed conduits - Methods using electromagnetic flow-meters (ISO 6817:1992)

Describes the principle and main design features of industrial electromagnetic flowmeters (both a.c. and pulsed d.c. versions) for the measurement of flow-rate in a closed conduit running full. Covers their installation, operation, performance and calibration.

Durchflußmessung von leitfähigen Flüssigkeiten in geschlossenen Leitungen - Verfahren mit magnetisch-induktiven Durchflußmeßgeräten (ISO 6817:1992)

Diese Internationale Norm beschreibt das Meßprinzip und die Hauptbestandteile eines magnetisch-induktiven Durchflußmeßgerätes und behandelt den Einbau, die Arbeitsweise, die Ausführung und die Kalibrierung von industriell genutzten Geräten. Diese Norm legt keine Sicherheitsanforderungen für den Gebrauch solcher Geräte unter sicherheitstechnisch bedeutsamen Bedingungen fest. Sie behandelt nicht die Anwendung von Geräten zur Messung von Flüssigmetallen und magnetisch verschmutzten Schlämmen und die Benutzung im medizinischen Bereich.

Mesure de débit d'un fluide conducteur dans les conduites fermées - Méthode par débitmètres électromagnétiques (ISO 6817:1992)

La présente Norme internationale décrit le principe et les principes fondamentaux de conception des débitmètres électromagnétiques mesurant le débit d'un liquide conducteur dans une conduite fermée remplie. Elle traite de leur installation, de leur fonctionnement, de leur performance et de leur étalonnage. La présente Norme internationale ne spécifie aucune règle de sécurité pour l'emploi des débitmètres dans les conditions environnementales dangereuses et ne s'applique pas au mesurage des boues perméables magnétiquement ni aux usages médicaux. Elle traite des débitmètres en version courant alternatif et courant continu pulsé.

Measurement of conductive liquid flow in closed conduits - Method using electromagnetic flowmeters

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SIST EN ISO 6817:1997
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
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
SIST EN ISO 6817:1997 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 6817:1997
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SIST EN ISO 6817:1997
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SIST EN ISO 6817:1997
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SIST EN ISO 6817:1997
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SIST EN ISO 6817:1997
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SIST EN ISO 6817:1997
First edition
1992-l 2-o 1
Measurement of conductive liquid flow in closed
conduits - Method using electromagnetic
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)
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SIST EN ISO 6817:1997
IS0 6817:1992(E)

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
. . . . . . . . . . . . . . . . . . . . . .
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
Case Postale 56 * CH-1211 Genke 20 l Switzerland
Printed in Switzerland
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SIST EN ISO 6817:1997
IS0 6817:1992(E)
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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SIST EN ISO 6817:1997
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SIST EN ISO 6817:1997
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.

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SIST EN ISO 6817:1997
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
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
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)
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
with a.c.-energized electromagnets.
quadrature voltage: That part of the electrode
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
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-
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.
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SIST EN ISO 6817:1997
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. . . .
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 so placed with respect to the magnetic field that
nD2 the path of the conductive liquid, flowing in the pipe,
. . .
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
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
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
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SIST EN ISO 6817:1997
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
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 electrodes. The primary device may contain
circuitry for deriving the reference signal.
- d.c. energized.
Figure3 shows an exploded view of an industrial
The pulsed direct current (d.c.) meter is one in which
primary device. The coils and the yoke are arranged
the field windings of the primary device are ener-
to produce a magnetic field, the meter tube is a
gized from a source creating a pulsating current.
non-magnetic material such as plastic, ceramic, al-
The meter samples the signal at zero magnetic field
uminium, brass or non-magnetic stainless steel. An
and zero adjusts, but does not differentiate against
insulating lining is used with metallic tubes to pre-
all other spurious signals.
vent the metal tube from short-circuiting the
The lining

electrode signal. may be glass, General guidance on various aspects of the primary

elastomer, plastic, ceramic, etc. (see annex A). The device is set out in 7.1 and physical features are

materials used for the lining and the electrodes are
considered in annex A.
/- FLanges
Power supply
Pipe with Insulating layer
Flow signal cable
Figure 2 - Elements of an industrial electromagnetic flowmeter
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SIST EN ISO 6817:1997
IS0 6817:1992(E)
1 Upper housing
2 Coil
3 Electrodes
4 Meter tube
5 Lining
6 Lower housing
Figure 3 -
Exploded view of the primary device of an electromagnetic flowmeter
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SIST EN ISO 6817:1997
IS0 6817:1992(E)
6.3 Secondary devices In a pulsed d.c. system, under ideal or reference
conditions, the peak-to-peak value of the electrode
signals, (VP + V,), is proportional to the flow velocity
Secondary devices carry out the following pro-
in the pipeline and J$ is also equal to Vn [see
figure 4a)], where VP = positive voltage and Vn =
negative voltage.
a) amplify and proc :ess the electrode and reference
signals to obtain a signa I proportional to flow;
In a practical situation, if the zero or “no-flow” signal
is offset in the positive direction by an amount Ve,
b) eliminate, as far as possible, spurious e.m.fs.
then the positive signal is (VP + I/e) and the negative
These include common mode and quadrature
signal is (& - I/e) [figure4b)]. Hence the overall
value of the electrode signal is (V, + VJ and the
offset zero is eliminated. The same applies if the
c) provide means of compensating for supply volt-
offset is in the negative direction.
age and frequency variations where necessary;
The system thus eliminates zero errors automati-
d ) provide means of compensating or minimizing
cally at all times and zero adjustment is not usually
magnetic field strength variations in the primary
required, either at start-up/commissioning or at any
device. This is important since it directly affects
time during subsequent operation.
repeatability of the voltage at the measurement
General guidance on the function and installation of
secondary devices is presented in 7.2.
Compensation is achieved by the following means:
a) a gain-compensated amplifier in which the gain
6.4 System output
is proportional to the supply frequency and in-
versely proportional to the supply voltage;
The system output can be one or more of the fol-
b) a system in which the output is proportional to
the ratio of the flow signal and a reference signal
a) analog direct current in accordance with IEC
derived from the field current. At a given flow-
rate both signals may vary with supply voltage
and frequency, but their ratio will remain con-
b) analog direct voltage in accordance with IEC
c) a system in which the field current is stabilized.
c) a frequency output in the form of scaled or un-
scaled pulses;
For alternating current (a.c.) energized systems with
unregulated coil current, the secondary device
d) digital.
measures the ratio of V/B (see clause 5). Voltages
other than the flow signal (v) may be picked up by
electrode leads. These voltages may be generated
by the varying flux intersecting a loop composed of
6.5 Effect of the liquid conductivity
the electrode leads, the electrodes, and the liquid
connecting the electrodes (transformer effect). Such
If the electrical conductivity of the liquid is uniform
a voltage will be approximately 90” out of phase with
in the measuring section of the meter, the electric
the flow signal. That portion which is 90’ out of
field distribution is independent of the liquid con-
phase is called “quadrature”. The remainder is
ductivity and therefore the meter output is generally
component. The “in-phase”
called the “in-phase”
independent of the liquid conductivity. Minimum op-
component is zeroed at no-flow during initial instal-
erational conductivity requirements should be ob-
lation, unless the flowmeters have a device which
tained from the manufacturers.
provides this function automatically.
The internal impedance of the primary device obvi-
If the coil current is regulated, the magnetic field is
ously depends upon the liquid conductivity, and very
considered to be constant and it is only necessary
large changes in this impedance may produce er-
to measure the electrode signal. If the coil current
rors in the output signal. If the conductivity is not
is not regulated, then, in order to compensate for
uniform throughout the meter, errors may also oc-
variations in the magnetic field, the secondary de-
cur. A heterogeneous fluid composed of small parti-
vice may use a reference signal obtained from the
cles uniformly distributed in a medium can be
primary element. This reference signal may be de-
considered as a homogeneous liquid.
rived from the supply voltage, the supply current, the
Deposition of electrically conducting layers on the
flux density in the metal or the flux density in the air
inside surface of the liner may also lead to errors.
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SIST EN ISO 6817:1997
ISO, 6817:1992(E)
6.6. Reynolds number effect
7 Installation desig’n and practice
In industrial, electromagnetic flowmeters, the effect
of Reynolds number is usually so small that for 7.1 Primary devices
practical purposes it can be ignored.
7.1 .I Size
6.7 Velocity profile effect
Usually the bore of the primary device tube will be
Distortions in velocity profiles may be caused by
the same as that of the adjacent pipework. If, in this
pipe fittings (bends, valves, reducers, etc.) placed
case, the mean axial velocity corresponding to the
upstream or downstream from the flowmeter; the
maximum flow-rate is less than that recommended
resulting flow patterns may have an influence on the
a primary devi’ce with a
by the manufacturer,
performance of the meter.
smaller bore should be used. A primary device with
a bore smaller than that of the adjacent pipework
In general, the user should *comply with the manu-
may also be used for other reasons, e.g. to reduce
facturer’s recommendations for installation in order
cost or in the interests of rationalization. Information
to minimize these effects.
on the allowable tolerances for matching the pipe

Flow pattern effects are described in and meter tube bores is given in IS0 9104.

Measurfng Interval
Measurlng Interval
al Ideal conditions
Random noise
No-flow signal
b) Practical condltlons
Figure 4 - Principle of pulsed d.c. (bipolar) system
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SIST EN ISO 6817:1997
IS0 6817:1992(E)
7.1.2 Layout
not be within the manufacturer’s stated accuracy. If
necessary, warning devices should be installed to

There is no theoretical restriction on the attitude at preserve measurement integrity. Partially-filled pri-

which a primary device may be mounted, provided mary device meters are used, for example in sew-

the pipe remains full at all times. Locations close to applications, but these
merit special

electrical equipment which may interfere with the consideration outside the scope of this International

flow measurement signal, or locations where cur-
rents may be induced in the primary device, should
be avoided. Electrode position
Since any gas bubbles will rise and collect at the top Effect of layout on velocity distribution
of the pipe, or sediment may collect at the bottom
of the pipe, the primary device should be mounted
Ideally, the magnetic field should be so arranged
so that neither electrode is in these positions (see
that the calibration factor is always the same, irre-
spective of the flow pattern. Though this can be done
in flowmeters with special electrode arrangements, Zero-checking provislon
it cannot be achieved if small electrodes are used.
In practice, when a flow velocity profile which is
In order to check the flowmeter zero, means should
significantly different from that in the original cali-
be provided to stop the flow through the primary
bration is presented to the electrode plane, an
device, leaving it filled with stationary liquid.
electromagnetic flowmeter may exhibit a shift in
calibration. The arrangement of pipe fittings up-
However, in the case of a synchronous d.c. pulsed
stream of the primary device is one of the factors
field supply with an automatically adjusting zero,
which can contribute to the creation of a particular
this provision may not be necessary.
velocity profile.
Precise data on the effects of flow disturbances is Multiphase flow through the primary device
not always available, but for most electromagnetic
flowmeters it is recommended that any source of
flow disturbance, such as a bend, should be at least Entrained solids
ten pipe diameters upstream of the electrode plane

if the performance is not to be altered by more than For the measurement of liquids containing abrasive

1 %. When the distance is unavoidably less than materials, vertical mounting is recommended to en-

this, the manufacturer’s advice should be sought. sure evenly distributed lining wear. Where there is

a possibility that material may settle in the primary
Swirling flow can also alter the calibration factor
device, it should be mounted vertically or provision
because, although flow components perpendicular
should be made to flush it through.
to the pipe axis cannot contribute to the flow-rate,

they may contribute to the signal. Furthermore, the A ring to protect the leading edge of the magnetic

amount and distribution of swirl arising from various flowmeter is sometimes used. This ring shall be de-

signed to ensure streamlined flow.
upstream pipe configurations, such as several
bends in different planes, is difficult to predict from
the geometry of the pipework. When swirling flow is Entrained gases
suspected, it is good practice to insert a swirl
reducer upstream of the primary device; some types
An electromagnetic flowmeter measures total vol-
of swirl reducers are described in IS0 7194.
ume flow. Entrained gases cause measurement in-
accuracies in direct relation to the volume
When the primary device is connected to the circuit
percentage of gas to liquid. Precautions should be
by means of conical pieces, the effect on the cali-
taken to reduce this effect by increasing the liquid
bration factor due to the irregular flow pattern may
pressure, e.g. by locating the primary device on the
be either reduced or amplified according to the type
high-pressure side of a restrictor such as a control
of irregularity (swirl, asymmetry, etc.) and the de-
valve, or by eliminating the entrained gas.
sign of the connecting piece (convergence, diver-
gence, value of total angle, etc.). Phase slippage Full pipe requirement
In the case of entrained solids and/or gases, relative
average motion of the phases can affect the per-

The primary device shall be mounted in such a formance. This condition is particularly likely if the

position that it will be completely filled with the liq- tube is mounted vertically. In such situations the

uid being metered, otherwise the measurement will user should consult the manufacturer.

---------------------- Page: 18 ----------------------
SIST EN ISO 6817:1997
IS0 6817:1-992(E)
7.1.3 Pipework connections Connecting pieces Design To minimize pressure loss and flow disturbances in
cases where an undersized meter is installed, it is
advisable to connect the primary device into the
When designing the piping system, access for in-
pipework by means of shallow tapered cone pieces
stalling and removing the primary device as well as

access to the electrical connections should be pro- (recommended maximum included angle 15”) (see

figure5). In this case, the inlet and outlet straight
vided. Means should be provided for adjusting and

aligning the adjacent pipework. Extra care should pipe sections shall be the same size as the

be taken during pipework construction to prevent flowmeter (see 7.1.2).
excessive strain on the primary device, both during
Eccentric taper pipes shall be used when the pipe-
and after installation.
line is horizontal, to prevent air pockets from form-
Every effort should be made to minimize piping
loads and resulting strains at the primary device
connecting flanges, particularly in plastic meters 7.1.4 Electrical installation
which are not intended to sustain piping loads. Per-
missible values should be checked with the manu- General requirements
The metered liquid and the primary device body
should be at the same potential, preferably earth Pipework adjustment
potential. In the case where cathodic protection is
used to protect buried pipework, this precaution be-
There should be means for adjusting the distance
comes essential (see
between pipework flanges used for mounting the
flowmeter and for aligning the adjacent pipework.
The connection between the liquid and the primary
device body may be made by contact with the adja-
It is essential that the primary device is correctly
cent pipework; or, where insulated or non-
aligned on the pipe axis when it is bolted into the
conductive pipework is used, by conductive
pipework. Wafer types require special care.
(earthing) rings or electrodes. Equipotential
Flange bolts should be tightened evenly and in
conductive links (usually copper braids) should be
moderation in order to avoid damage to the lining.
fitted across both flange joints (see figure6).
The manufacturer should state the maximum per-
The manufacturer’s instructions should be carefully
missible torque.
followed for interconnections between the primary
Care should be taken when handling

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