ISO 10790:1999
(Main)Measurement of fluid flow in closed conduits — Guidance to the selection, installation and use of Coriolis meters (mass flow, density and volume flow measurements)
Measurement of fluid flow in closed conduits — Guidance to the selection, installation and use of Coriolis meters (mass flow, density and volume flow measurements)
Mesure de débit des fluides dans les conduites fermées — Lignes directrices pour la sélection, l'installation et l'utilisation des mesureurs à effet Coriolis (mesurages de débit-masse, masse volumique et débit-volume)
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 10790
Second edition
1999-05-01
Measurement of fluid flow in closed
conduits — Guidance to the selection,
installation and use of Coriolis meters
(mass flow, density and volume flow
measurements)
Mesure de débit des fluides dans les conduites fermées — Lignes
directrices pour la sélection, l'installation et l'utilisation des mesureurs à
effet Coriolis (mesurages de débit-masse, masse volumique et débit-
volume)
Reference number
A
ISO 10790:1999(E)
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ISO 10790:1999(E)
Contents
1 Scope .1
2 Terms and definitions .1
3 Coriolis meter selection criteria .3
4 Inspection and compliance.8
5 Mass flow measurement .8
6 Density measurement under metering conditions.11
7 Volume flow measurement under metering conditions.14
8 Additional measurements.16
Annex A (informative) Calibration techniques .19
Annex B (informative) Secondary containment of Coriolis meters.23
Annex C (informative) Coriolis meter specifications.25
Annex D (informative) Mass fraction measurement examples .26
Bibliography.29
© ISO 1999
All rights reserved. Unless otherwise specified, 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 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
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© ISO ISO 10790:1999(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 10790 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in
closed conduits, Subcommittee SC 12, Mass methods.
This second edition cancels and replaces the first edition (ISO 10790:1994), which has been extended to include all
measured and inferred parameters obtainable from a Coriolis meter including mass flow, density, volume flow and
other related parameters.
Annexes A, B, C and D of this International Standard are for information only.
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ISO 10790:1999(E) © ISO
Introduction
This International Standard has been prepared as a guide for those concerned with the selection, testing,
inspection, operation and calibration of Coriolis meters (Coriolis meter assemblies) for any kind of fluid.
A list of related standards is given in the bibliography.
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INTERNATIONAL STANDARD © ISO ISO 10790:1999(E)
Measurement of fluid flow in closed conduits — Guidance
to the selection, installation and use of Coriolis meters
(mass flow, density and volume flow measurements)
1 Scope
This International Standard gives guidelines for the selection, installation, calibration, performance and operation of
Coriolis meters for the determination of mass flow, density, volume flow and other related parameters of fluids. It
also gives appropriate considerations regarding the fluids to be measured.
The primary purpose of Coriolis meters is to measure mass flow. However, some of these meters offer additional
possibilities for determining the density and temperature of fluids. From the measurement of these three
parameters, volume flow and other related parameters can be determined.
The content of this International Standard is primarily applied to the metering of liquids. This International Standard
also gives guidance within specified limits, to the metering of other fluids, mixtures of solids or gas in liquids, and
mixtures of liquids. Although Coriolis meters may be used for gas measurement, specific guidance for gas
measurement is not within the scope of this International Standard.
2 Terms and definitions
For the purpose of this International Standard, the following terms and definitions apply.
2.1
Coriolis meter
device consisting of a flow sensor (primary device) and a transmitter (secondary device) which primarily measures
the mass flow by means of the interaction between a flowing fluid and the oscillation of a tube or tubes; it may also
provide measurements of the density and the process temperature of the fluid
2.2
flow sensor (primary device)
mechanical assembly consisting of an oscillating tube, drive system, measurement sensor(s), supporting structure
and housing
2.2.1
oscillating tube(s)
tube(s) through which the fluid to be measured flows
2.2.2
drive system
means for inducing the oscillation of the tube(s)
2.2.3
sensing device
sensor to detect the effect of the Coriolis force and to measure the frequency of the tube oscillations
2.2.4
supporting structure
support for the oscillating tube(s)
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ISO 10790:1999(E) © ISO
2.2.5
housing
environmental protection of the flow sensor
2.2.6
secondary containment
housing designed to provide protection to the environment in the event of tube failure
2.3
transmitter (secondary device)
electronic control system providing the drive and transforming the signals from the flow sensor, to give output(s) of
measured and inferred parameters; it also provides corrections derived from parameters such as temperature
2.4
flow rate
ratio of the quantity of fluid passing through the cross-section of the flowsensor and the time taken for this quantity
to pass through this section
2.4.1
mass flow rate
flow rate in which the quantity of fluid which passes is expressed as mass
2.4.2
volume flow rate
flow rate in which the quantity of fluid which passes is expressed as volume
2.5
accuracy of measurement
[1]
closeness of the agreement between the result of a measurement and a true value of the measurand [VIM ]
2.6
repeatability
closeness of the agreement between the results of successive measurements of the
[1]
same measurand carried out under the same conditions of measurement [VIM ]
2.7
uncertainty of measurement
parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could
[1]
reasonably be attributed to the measurand [VIM ]
2.8
error
[1]
result of a measurement minus a true value of the measurand [VIM ]
2.9
calibration factor(s)
numerical factor(s) unique to each sensor derived during sensor calibration, which when programmed into the
transmitter ensures that the meter performs to its stated specification
2.9.1
flow calibration factor(s)
associated with mass flow measurement
2.9.2
density calibration factor(s)
associated with density measurement
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© ISO ISO 10790:1999(E)
2.10
zero offset
measurement output indicated under zero flow conditions, usually as a result of stress being applied to the
oscillating tubes by the surrounding pipework and by process conditions
NOTE The zero offset can be reduced by means of a zero adjustment procedure.
2.11
zero stability
magnitude of the meter output at zero flow after the zero adjustment procedure has been completed, expressed by
the manufacturer as an absolute value in mass per unit time
NOTE The stated value for zero stability is valid for stable conditions where the fluid is free of bubbles and heavy
sediment.
2.12
flashing
phenomenon which occurs when the line pressure drops to, or below, the vapour pressure of the liquid
NOTE This is often due to pressure drops caused by an increase in the liquid velocity.
2.13
cavitation
phenomenon related to and following flashing if the pressure recovers causing the vapour bubbles to collapse
(implode)
3 Coriolis meter selection criteria
3.1 General
The Coriolis meter should be selected to measure parameters within the required range and accuracy.
Consideration should be given to the following points when selecting a Coriolis meter.
3.2 Accuracy
The expression of accuracy varies depending on the parameter to which it applies. For specific recommendations
on mass flow, density and volume flow accuracies, see 5.2, 6.3 and 7.3, respectively. For other parameters see
clause 8.
NOTE Manufacturers’ accuracy statements should be given for specified reference conditions. If the conditions of use are
significantly different from those of the original calibration, the meter's performance may be affected.
3.3 Physical installation
3.3.1 General
The manufacturer should describe the preferred installation arrangement and state any restrictions of use. See
annex C.
The installation arrangement should be designed to provide a maximum operating lifetime. If needed, strainers,
filters, air and/or vapour eliminators or other protective devices should be placed upstream to the meter for the
removal of solids or vapours that could cause damage or provoke errors in measurement.
Coriolis meters are generally placed in the mainstream of the flow but can also be placed in a by-pass arrangement
for density measurements.
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ISO 10790:1999(E) © ISO
3.3.2 Installation criteria
Consideration should be given to the following points:
a) the space required for the Coriolis meter installation, including provision for external prover or master-meter
connections, should in-situ calibration be required;
b) the class and type of pipe connections and materials, as well as the dimensions of the equipment to be used;
c) the hazardous area classification;
d) the climatic and environmental effects on the sensor, for instance temperature, humidity, corrosive
atmospheres, mechanical shock, vibration and electromagnetic field;
e) the mounting and support requirements.
3.3.3 Full-pipe requirement
The primary device should be mounted such that the oscillating tube(s) fill completely with the fluid being metered;
this will prevent the measuring performance of the instrument from being impaired. The manufacturer should state
the means, if any, required to purge or drain gases or liquids from the instrument.
3.3.4 Orientation
Plugging, coating, trapped gas, trapped condensate or settlement of solids can affect the meter's performance. The
orientation of the sensor will depend on the intended application of the meter and the geometry of the oscillating
tube(s). The orientation of the Coriolis meter should be recommended by the manufacturer.
3.3.5 Flow conditions and straight length requirements
The performance of a Coriolis meter is usually not affected by swirling fluid or non-uniform velocity profiles induced
by upstream- or downstream-piping configurations. Although special straight-piping lengths are normally not
required, good piping practices should be observed at all times.
3.3.6 Valves
Valves upstream and downstream to a Coriolis meter, installed for the purpose of isolation and zero adjustment, can
be of any type, but should provide tight shutoff. Control valves in series with a Coriolis meter should be installed
downstream in order to maintain the highest possible pressure in the meter and thus reduce the chance of
cavitation or flashing.
3.3.7 Cleaning
For certain applications (for instance hygienic services), the Coriolis meter may require in-situ cleaning which can
be accomplished by:
a) mechanical means (using a pig or ultrasonically);
b) self-draining;
c) hydrodynamic means:
sterilization (steaming-in-place, SIP);
chemical or biological (cleaning-in-place, CIP).
NOTE 1 Care should be taken to avoid cross-contamination after cleaning fluids have been used.
NOTE 2 Chemical compatibility should be established between the sensor wetted-materials, process fluid and cleaning fluid.
3.3.8 Hydraulic and mechanical vibrations
The manufacturer should specify the operating frequency range of the instrument to enable assessment of possible
influences of process or other external mechanically imposed frequencies. It is possible that the performance of the
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© ISO ISO 10790:1999(E)
meter may be influenced by frequencies other than the operating frequencies. These effects can largely be
addressed by appropriate mounting or clamping of the instrument.
In environments with high mechanical vibrations or flow pulsations, consideration should be given to the use of
pulsation damping devices (see 3.4.7) and/or vibration isolators and/or flexible connections.
3.3.9 Flashing and/or cavitation
The relatively high fluid velocities which often occur in Coriolis meters, cause local dynamic pressure drops inside
the meter which may result in flashing and/or cavitation.
Both flashing and cavitation in Coriolis meters (and immediately upstream and/or downstream of them), should be
avoided at all times. Flashing and cavitation may cause measurement errors and may damage the sensor.
3.3.10 Pipe stress and torsion
The flow sensor will be subjected to axial, bending and torsional forces during operation. Changes in these forces,
resulting from variations in process temperature and/or pressure, can affect the performance of the Coriolis meter.
Care should be taken to ensure that no forces are exerted on the meter from clamping arrangements.
Measures should also be taken to prevent excessive stresses from being exerted on the Coriolis meter by
connecting pipes. Under no circumstances should the Coriolis meter be used to align the pipework.
3.3.11 Cross-talk between sensors
If two or more Coriolis meters are to be mounted close together, interference through mechanical coupling may
occur. This is often referred to as cross-talk. The manufacturer should be consulted for methods of avoiding cross-
talk.
3.4 Effects due to process conditions and fluid properties
3.4.1 General
Variations in fluid properties such as density, viscosity and process conditions such as pressure and temperature,
may influence the meter’s performance. These effects have influences which differ depending on which parameter
is of interest. Refer to clauses 5.3, 6.4, 7.4 and 8.3.
3.4.2 Application and fluid properties
In order to identify the optimum meter for a given application, it is important to establish the range of conditions to
which the Coriolis meter will be subjected. These conditions should include:
a) the operating flow rates and the following flow characteristics: unidirectional or bi-directional, continuous,
intermittent or fluctuating;
b) the range of operating densities;
c) the range of operating temperatures;
d) the range of operating pressures;
e) the pressure on the liquid adequate to prevent cavitation and flashing;
f) the permissible pressure loss;
g) the range of operating viscosities;
h) the properties of the metered fluids, including vapour pressure, two-phase flow and corrosiveness;
i) the effects of corrosive additives or contaminants on the meters and the quantity and size of foreign matter,
including abrasive particles, that may be carried in the liquid stream.
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ISO 10790:1999(E) © ISO
3.4.3 Multiphase flow
Liquid mixtures, homogeneous mixtures of solids in liquids or homogeneous mixtures of liquids with low ratios of
gas, may be measured satisfactorily in most cases. Multiphase applications involving non-homogeneous mixtures
can cause additional measurement errors and in some cases can stop operation. Care should be taken to ensure
that gas bubbles or condensate droplets are not trapped in the meter.
3.4.4 Influence of process fluid
Erosion, corrosion and deposition of material on the inside of the vibrating tube(s) (sometimes referred to as
coating) can initially cause measurement errors in flow and density, and in the longer term, sensor failure.
3.4.5 Temperature effects
A change in temperature will affect the properties of sensor materials, and thus will influence the response of the
sensor. A means of compensation for this effect is usually incorporated in the transmitter.
3.4.6 Pressure effects
Static pressure changes can affect the accuracy of the sensor, the extent of which should be specified by the
manufacturer. These changes are not normally compensated except in cases of certain precision measurements
and certain meter designs and sizes.
3.4.7 Pulsating flow effects
Coriolis meters generally are able to perform under pulsating flow conditions. However, there may be circumstances
where pulsations can affect the performance of the meter (see 3.3.8). The manufacturers’ recommendations should
be observed regarding the application and the possible use of pulsation damping devices.
3.4.8 Viscosity effects
Higher viscosity fluids may draw energy from the Coriolis excitation system particularly at the start of flow.
Depending on the meter design, this phenomenon may cause the sensor tubes to momentarily stall until the flow is
properly established. This phenomenon should normally induce a temporary alarm condition in the transmitter.
3.5 Pressure loss
A loss in pressure will occur as the fluid flows through the sensor. The magnitude of this loss will be a function of the
size and geometry of the oscillating tube(s), the mass flow rate (velocity) and dynamic viscosity of the process fluid.
Manufacturers should specify the loss in pressure which occurs under reference conditions and should provide the
information necessary to calculate the loss in pressure which occurs under operating conditions. The overall
pressure of the system should be checked to ensure that it is sufficiently high to accommodate the loss in pressure
across the meter.
3.6 Safety
3.6.1 General
The meter should not be used under conditions which are outside the meter's specification. Meters also should
conform to any necessary hazardous area classifications. The following additional safety considerations should be
made.
3.6.2 Hydrostatic pressure test
The wetted parts of the fully-assembled flow sensor should be hydrostatically tested in accordance with the
appropriate standard.
3.6.3 Mechanical stress
The meter should be designed to withstand all loads originating from the oscillating tube(s) system, temperature,
pressure and pipe vibration. The user should respect the limitations of the sensor at all times.
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© ISO ISO 10790:1999(E)
3.6.4 Erosion
Fluids containing solid particles or cavitation can cause erosion of the measuring tube(s) during flow. The effect of
erosion is dependent on meter size and geometry, particle size, abrasives and velocity. Erosion should be assessed
for each type of use of the meter.
3.6.5 Corrosion
Corrosion, including galvanic corrosion, of the wetted materials can adversely affect the operating lifetime of the
sensor. The construction material of the sensor should be selected to be compatible with process fluids and
cleaning fluids. Special attention should be given to corrosion and galvanic effects in no-flow or empty-pipe
conditions. All process-wetted materials should be specified.
3.6.6 Housing design
The housing should be designed primarily to protect the flowsensor from deleterious effects from its surrounding
environment (dirt, condensation and mechanical interference) which might interfere with operation. If the vibrating
tube(s) of the Coriolis meter were to fail, the housing containing the tube(s) would be exposed to the process fluid
and conditions which could possibly cause housing failure. It is important to take into consideration the following
possibilities:
a) the pressure within the housing might exceed the design limits;
b) the fluid might be toxic, corrosive or volatile and might leak from the housing.
In order to avoid such problems, certain housing designs provide:
secondary pressure containment;
burst discs or pressure-relief valves, fluid drains or vents, etc.
For guidelines on specifying secondary pressure containment, see annex B.
3.6.7 Cleaning
For general guidelines see 3.3.7.
Care should be taken to ensure that cleaning conditions (fluids, temperatures, flow rates, etc.) have been selected
to be compatible with the materials of the Coriolis meter .
3.7 Transmitter (secondary device)
Coriolis meters are multivariable instruments providing a wide range of measurement data from only a single point
in the process. In selecting the most appropriate transmitter, consideration should be given to:
a) the electrical, electronic, climatic and safety compatibility;
b) the mounting, i.e. integrally or remotely mounted;
c) the required number and type of outputs;
d) the ease and security of programming;
e) the outputs demonstrating adequate stability and reasonable response times, and in the case of an analogue
output including the minimum and maximum span adjustments;
f) the output(s) indicating system errors;
g) the required input options, for instance remote zero adjustment, totalizer resetting, alarm acknowledgement;
h) the type of digital communication.
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ISO 10790:1999(E) © ISO
4 Inspection and compliance
As Coriolis meters are an integral part of the piping (in-line instrumentation), it is essential that the instrument be
subjected to testing procedures similar to those applied to other in-line equipment.
In addition to the instrument calibration and/or performance checks, the following optional tests may be performed
to satisfy the mechanical requirements:
dimensional check;
additional hydrostatic test, in accordance with a traceable procedure, as specified by the user;
radiographic and/or ultrasonic examination of the primary device to detect internal defects (i.e. inclusions) and
verify weld integrity;
Results of the above tests should be presented in a certified report, when requested.
In addition to the above reports, the following certificates should be available at final inspection:
material certificates, for all pressure-containing parts;
certificate of conformance (electrical area classifications);
certificate of compliance;
calibration certificate and test results.
5 Mass flow measurement
5.1 Apparatus
5.1.1 Principle of operation
Coriolis meters operate on the principle that inertia forces are generated whenever a particle in a rotating body
moves relative to the body in a direction toward or away from the centre of rotation. This principle is shown in
Figure 1.
Figure 1 — Principle of operation of a Coriolis meter
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© ISO ISO 10790:1999(E)
A particle of mass dm slides with constant velocity v in a tube T which is rotating with angular velocity w about a
fixed point P. The particle undergoes an acceleration which can be divided into two components:
2
a) a radial acceleration (centripetal) equal to w · and directed towards P;
a r
r
b) a transverse acceleration a (Coriolis) equal to 2w·v at right angles to a and in the direction shown in Figure 1.
t r
To impart the Coriolis acceleration a to the particle, a force of magnitude 2w·v·dm is required in the direction of a .
t t
The oscillating tube exerts this force on the particle. The particle reacts to this force with an equal force called the
Coriolis force, DF , which is defined as follows:
C
DF = 2w·v·dm
C
When a fluid of density r flows at constant velocity v along an oscillating tube rotating as shown in Figure 1, any
length Dx of the oscillating tube experiences a transverse Coriolis force of magnitude DF = 2w·v·r·A·Dx where A is
C
the cross-sectional area of the oscillating tube interior.
Since the mass flow rate q can be expressed as:
m
q = v·r·A (1)
m
The transverse Coriolis force DF can therefore be expressed as follows:
C
D = 2w· ·D (2)
F q x
C m
Hence, the (direct or indirect) measurement of the Coriolis force exerted by the flowing fluid on a rotating tube can
provide a measurement of the mass flow rate. This is the principle of operation of a Coriolis meter.
5.1.2 Coriolis sensor
In commercial designs of Coriolis meters, inertia forces are generated by oscillating the tube rather than from a
continuous rotary motion.
The smallest driving force required to keep the tube in constant oscillation occurs when the frequency of oscillation
is at, or close to, the natural frequency of the filled tube.
In most meters the flow tube is fixed between two points and oscillated at a position midway between these two
points, thus giving rise to opposite oscillatory rotations on the two halves of the tube. Meters can have a single tube
or two parallel tubes which can be straight or looped.
When no flow is present, the phases of the relative displacements at the sensing points are identical, but when flow
is present Coriolis forces act on the oscillating tube(s), causing a small displacement/deflection or twist which can
be observed as a phase difference between the sensing points.
Coriolis forces (and hence distortion of the tube) only exist when both axial motion and forced oscillation are
present. When there is forced oscillation but no flow, or flow with no oscillation, no deflection will occur and the
meter will give no output.
The sensor is characterized by flow calibration factors which are derived during manufacture and calibration. These
values are unique for each sensor and are normally recorded on a calibration certificate and/or a data plate secured
to the sensor housing.
5.1.3 Coriolis transmitter
A Coriolis meter requires a transmitter to provide the drive energy and to process the subsequent signals. It is
necessary to match the transmitter to the sensor by entering the calibration factors from the sensor data plate.
The mass flow rate is usually integrated over time in the transmitter to give the total mass.
The transmitter may contain application software which can be used to evaluate additional parameters but they
require further configuration. In the case of the measurement of density or volume, output requirements necessitate
the entry of other coefficients into the software. All outputs are usually scaled separately.
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ISO 10790:1999(E) © ISO
5.2 Accuracy
The term accuracy, expressed as a percentage of the reading, is often used by manufacturers and users as a
means of quantifying the expected error limits. For mass flow, the term accuracy includes the combined effects of
linearity, repeatability, hysteresis and zero stability.
Linearity, repeatability and hysteresis are combined and expressed as a percentage of the reading. Zero stability is
given as a separate parameter in mass per unit time. In order to determine the complete accuracy value, it is
necessary to calculate zero stability as a percentage of the reading at a specified flow rate, and add this value to the
combined effects of linearity, repeatability and hysteresis.
Repeatability is often given as a separate parameter, expressed as a percentage of the reading. It is calculated in a
similar way to accuracy.
Accuracy and repeatability statements are usually made for reference conditions which are specified by the
manufacturer. These reference conditions should include temperature, pressure, density range and flow range.
5.3 Factors affecting mass flow measurement
5.3.1 General
Refer also to annex C for further details.
5.3.2 Density and viscosity
Density and viscosity usually have a minor effect on measurements of mass flow. Consequently, compensation is
not normally necessary. However, for some designs and sizes of meters, density changes may induce an offset in
the meter output at zero flow and/or a change in the meter calibration factor. The offset can be eliminated by
performing a zero adjustment (see 5.4) under operating conditions. See 3.4.8 for viscosity effects.
5.3.3 M
...
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