Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full - Part 6: Wedge meters (ISO 5167-6:2019)

This document specifies the geometry and method of use (installation and operating conditions) of wedge meters when they are inserted in a conduit running full to determine the flow rate of the fluid flowing in the conduit.
NOTE 1    As the uncertainty of an uncalibrated wedge meter can be too large for a particular application, it could be deemed essential to calibrate the flow meter according to Clause 7.
This document gives requirements for calibration which, if applied, are for use over the calibrated Reynolds number range. Clause 7 could also be useful guidance for calibration of meters of similar design but which fall outside the scope of this document.
It also provides background information for calculating the flow rate and is applicable in conjunction with the requirements given in ISO 5167‑1.
This document is applicable only to wedge meters in which the flow remains subsonic throughout the measuring section and where the fluid can be considered as single-phase. Uncalibrated wedge meters can only be used within specified limits of pipe size, roughness, beta (or wedge ratio) and Reynolds number. It is not applicable to the measurement of pulsating flow. It does not cover the use of uncalibrated wedge meters in pipes whose internal diameter is less than 50 mm or more than 600 mm, or where the pipe Reynolds numbers are below 1 × 104.
NOTE 2    A wedge meter has a primary element which consists of a wedge-shaped restriction of a specific geometry. Alternative designs of wedge meters are available; however, at the time of writing there is insufficient data to fully characterize these devices, and therefore these meters are calibrated in accordance with Clause 7.

Durchflussmessung von Fluiden mit Drosselgeräten in voll durchströmten Leitungen mit Kreisquerschnitt - Teil 6: Keil-Durchflussmesser (ISO 5167-6:2019)

Dieses Dokument legt die Geometrie und Anwendungsverfahren (Einbau  und Betriebsbedingungen) von in voll durchströmten Leitungen eingesetzten Keil Durchflussmessern fest, um den Durchfluss der Fluid-strömung in der Leitung zu bestimmen.
ANMERKUNG 1 Da die Unsicherheit eines nicht kalibrierten Keil Durchflussmessers für eine bestimmte Anwendung zu groß sein kann, könnte es als erforderlich angesehen werden, den Durchflussmesser nach Abschnitt 7 zu kalibrieren.
Dieses Dokument enthält Anforderungen an die Kalibrierung, die, wenn sie angewendet werden, für den kalibrierten Bereich der Reynoldszahlen gelten. Abschnitt 7 könnte auch ein nützlicher Leitfaden für die Kalibrierung von Durchflussmessern ähnlicher Ausführung sein, die jedoch nicht in den Anwendungsbereich des vorliegenden Dokuments fallen.
Es gibt auch Hintergrundinformationen für die Durchflussberechnung und gilt in Verbindung mit den in ISO 5167 1 festgelegten Anforderungen.
Dieses Dokument ist nur auf Keil Durchflussmesser anwendbar, in denen die Strömung in allen Messquer-schnitten im Unterschallbereich bleibt und das Fluid als einphasig betrachtet werden kann. Nicht kalibrierte Keil Durchflussmesser können nur innerhalb festgelegter Grenzen von Rohrweite, Rauheit β (oder Keilver¬hältnis) und Reynoldszahl angewendet werden. Es ist nicht für die Messung von pulsierender Strömung anwendbar. Er behandelt nicht die Anwendung von nicht kalibrierten Keil Durchflussmessern bei Rohren, deren Innendurchmesser geringer als 50 mm oder größer als 600 mm ist, oder wenn die Rohr Reynoldszahlen unter 1 × 104 liegen.
ANMERKUNG 2 Ein Keil Durchflussmesser verfügt über ein Primärelement, das aus einer keilförmigen Verengung mit spezifischer Geometrie besteht. Es stehen alternative Ausführungen von Keil Durchflussmessern zur Verfügung; zum Zeitpunkt der Erstellung der Norm gibt es jedoch nicht genügend Daten, um diese Geräte vollständig zu beschreiben, und deshalb werden diese Durchflussmesser nach Abschnitt 7 kalibriert.

Mesure de débit des fluides au moyen d'appareils déprimogènes insérés dans des conduites en charge de section circulaire - Partie 6: Débitmètres à coin (ISO 5167-6:2019)

Le présent document spécifie la géométrie et le mode d'emploi (conditions d'installation et d'utilisation) de débitmètres à coin insérés dans une conduite en charge dans le but de déterminer le débit du fluide s'écoulant dans cette conduite.
NOTE 1    Étant donné que l'incertitude d'un débitmètre à coin non étalonné risque d'être trop grande pour une application particulière, l'étalonnage du débitmètre conformément à l'Article 7 pourrait être considéré comme essentiel.
Le présent document fournit des exigences relatives à l'étalonnage, qui, si elles sont appliquées, sont destinées à être utilisées sur la plage des nombres de Reynolds qui a été étalonnée. L'Article 7 peut également fournir des préconisations utiles pour l'étalonnage des appareils de mesure de conception similaire, mais qui n'entrent pas dans le domaine d'application du présent document.
Il fournit également des informations de fond nécessaires au calcul du débit et il est applicable conjointement avec les exigences stipulées dans l'ISO 5167-1.
Le présent document est applicable uniquement aux débitmètres à coin pour lesquels l'écoulement reste subsonique dans tout le tronçon de mesure et où le fluide peut être considéré comme monophasique. Les débitmètres à coin non étalonnés ne peuvent être utilisés que dans des limites spécifiées de diamètre de conduite, de rugosité, de valeur de bêta (ou rapport du coin) et de nombre de Reynolds. Il n'est pas applicable au mesurage d'un écoulement pulsé. Il ne couvre pas l'utilisation de débitmètres à coin non étalonnés dans des conduites dont le diamètre intérieur est inférieur à 50 mm ou supérieur à 600 mm, ni les cas où les nombres de Reynolds rapportés à la tuyauterie sont inférieurs à 1 × 104.
NOTE 2    Un débitmètre à coin comporte un élément primaire composé d'une restriction en forme de coin de géométrie spécifique. D'autres conceptions de débitmètres à coin sont possibles; cependant, au moment de la rédaction du présent document les données permettant de caractériser complètement ces appareils étaient insuffisantes et ces derniers sont donc étalonnés conformément à l'Article 7.

Merjenje pretoka fluida na osnovi tlačne razlike, povzročene z napravo, vstavljeno v polno zapolnjen vod s krožnim prerezom - 6. del: Merilniki klinov (ISO 5167-6:2019)

Ta standard določa geometrijo in metodo uporabe (namestitev in pogoji delovanja) merilnikov klinov, kadar so ti vstavljeni v polno zapolnjen vod za ugotavljanje stopnje pretoka fluida skozi vod. Ta dokument podaja zahteve za umerjanje, ki se v ustreznem primeru uporabljajo v območju umerjanja Reynoldsovega števila. Točko 7 je mogoče uporabiti kot koristno vodilo za umerjanje merilnikov podobne zasnove, ki ne spadajo na področje uporabe tega dokumenta. Prav tako podaja dodatne informacije za izračun stopnje pretoka in se uporablja skupaj z zahtevami iz standarda ISO 5167-1. Ta dokument se uporablja samo za merilnike klinov, ki v predelu merjenja ohranjajo podzvočen pretok in pri katerih se lahko fluid obravnava kot enofazen. Neumerjeni merilniki klinov se lahko uporabljajo samo v okviru določenih omejitev glede velikosti cevi, hrapavosti, koeficienta beta (ali razmerja klinov) in Reynoldsovega števila. Ne uporablja se za merjenje utripajočega pretoka. Ne obravnava uporabe neumerjenih merilnikov klinov v ceveh z notranjim premerom pod 50 mm ali nad 600 mm, ali pri katerih so Reynoldsova števila za cevi manj kot 1 × 104.

General Information

Status
Published
Publication Date
01-Oct-2019
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
02-Oct-2019
Completion Date
02-Oct-2019

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SLOVENSKI STANDARD
SIST EN ISO 5167-6:2019
01-december-2019

Merjenje pretoka fluida na osnovi tlačne razlike, povzročene z napravo, vstavljeno

v polno zapolnjen vod s krožnim prerezom - 6. del: Merilniki klinov (ISO 5167-
6:2019)

Measurement of fluid flow by means of pressure differential devices inserted in circular

cross-section conduits running full - Part 6: Wedge meters (ISO 5167-6:2019)

Durchflussmessung von Fluiden mit Drosselgeräten in voll durchströmten Leitungen mit

Kreisquerschnitt - Teil 6: Keil-Durchflussmesser (ISO 5167-6:2019)
Mesure de débit des fluides au moyen d'appareils déprimogènes insérés dans des

conduites en charge de section circulaire - Partie 6: Débitmètres à coin (ISO 5167-

6:2019)
Ta slovenski standard je istoveten z: EN ISO 5167-6:2019
ICS:
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
SIST EN ISO 5167-6:2019 en,fr,de

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

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SIST EN ISO 5167-6:2019
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SIST EN ISO 5167-6:2019
EN ISO 5167-6
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2019
EUROPÄISCHE NORM
ICS 17.120.10
English Version
Measurement of fluid flow by means of pressure
differential devices inserted in circular cross-section
conduits running full - Part 6: Wedge meters (ISO 5167-
6:2019)

Mesure de débit des fluides au moyen d'appareils Durchflussmessung von Fluiden mit Drosselgeräten in

déprimogènes insérés dans des conduites en charge de voll durchströmten Leitungen mit Kreisquerschnitt -

section circulaire - Partie 6: Débitmètres à coin (ISO Teil 6: Keil-Durchflussmesser (ISO 5167-6:2019)

5167-6:2019)
This European Standard was approved by CEN on 23 September 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 5167-6:2019 E

worldwide for CEN national Members.
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SIST EN ISO 5167-6:2019
EN ISO 5167-6:2019 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 5167-6:2019
EN ISO 5167-6:2019 (E)
European foreword

The text of ISO 5167-6:2019 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 5167-6:2019 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.

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 5167-6:2019 has been approved by CEN as EN ISO 5167-6:2019 without any

modification.
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SIST EN ISO 5167-6:2019
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SIST EN ISO 5167-6:2019
INTERNATIONAL ISO
STANDARD 5167-6
First edition
2019-02
Measurement of fluid flow by means of
pressure differential devices inserted
in circular cross-section conduits
running full —
Part 6:
Wedge meters
Mesure de débit des fluides au moyen d'appareils déprimogènes
insérés dans des conduites en charge de section circulaire —
Partie 6: Débitmètres à coin
Reference number
ISO 5167-6:2019(E)
ISO 2019
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Principles of the method of measurement and computation ................................................................................ 2

5 Wedge meters .......................................................................................................................................................................................................... 3

5.1 Field of application .............................................................................................................................................................................. 3

5.2 General shape ........................................................................................................................................................................................... 4

5.3 Material and manufacture ............................................................................................................................................................. 5

5.4 Pressure tappings ................................................................................................................................................................................. 5

5.5 Discharge coefficient, C .....................................................................................................................................................................6

5.5.1 Limits of use ......................................................................................................................................................................... 6

5.5.2 Discharge coefficient of the wedge meter .................................................................................................. 6

5.6 Expansibility [expansion] factor, ε ........................................................................................................................................ 7

5.7 Uncertainty of the discharge coefficient, C ......................................................................................................................7

5.8 Uncertainty of the expansibility [expansion] factor, ε ......................................................................................... 7

5.9 Pressure loss ............................................................................................................................................................................................. 7

6 Installation requirements........................................................................................................................................................................... 8

6.1 General ........................................................................................................................................................................................................... 8

6.2 Minimum upstream and downstream straight lengths for installations between

various fittings and the wedge meter .................................................................................................................................. 8

6.3 Additional specific installation requirements for wedge meters ................................................................ 8

6.3.1 Circularity and cylindricality of pipes upstream and downstream of the

wedge meter ........................................................................................................................................................................ 8

6.3.2 Roughness of the upstream and downstream pipe ........................................................................... 9

6.3.3 Positioning of a thermowell ................................................................................................................................... 9

6.3.4 Bidirectional wedge meters ................................................................................................................................... 9

7 Flow calibration of wedge meters ...................................................................................................................................................... 9

7.1 General ........................................................................................................................................................................................................... 9

7.2 Test facility .................................................................................................................................................................................................. 9

7.3 Meter installation.................................................................................................................................................................................. 9

7.4 Design of the test programme .................................................................................................................................................10

7.5 Reporting the calibration results .........................................................................................................................................10

7.6 Uncertainty analysis of the calibration ...........................................................................................................................10

7.6.1 General...................................................................................................................................................................................10

7.6.2 Uncertainty of the test facility ...........................................................................................................................10

7.6.3 Uncertainty of the wedge meter ......................................................................................................................10

Annex A (informative) Table of expansibility [expansion] factor .......................................................................................11

Annex B (informative) Use of Kd parameter ............................................................................................................................................12

Bibliography .............................................................................................................................................................................................................................13

© ISO 2019 – All rights reserved iii
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(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 2, Pressure differential devices.
A list of all the parts in the ISO 5167 series can be found on the ISO website.
iv © ISO 2019 – All rights reserved
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(E)
Introduction

ISO 5167, divided into six parts, covers the geometry and method of use (installation and operating

conditions) of orifice plates, nozzles, Venturi tubes, cone and wedge meters when they are inserted in a

conduit running full to determine the flow rate of the fluid flow in the conduit. It also gives necessary

information for calculating the flow rate and its associated uncertainty.

ISO 5167 is applicable only to pressure differential devices in which the flow remains subsonic

throughout the measuring section and where the fluid can be considered as single-phase, but it is not

applicable to the measurement of pulsating flow. Furthermore, each of these devices can only be used

within specified limits of pipe size and Reynolds number.

ISO 5167 deals with devices for which direct calibration experiments have been made, sufficient

in number, spread and quality to enable coherent systems of application to be based on their results

and coefficients to be given with certain predictable limits of uncertainty. However, for wedge meters

calibrated in accordance with Clause 7, a wider range of pipe size, β and Reynolds number can be

considered.

The devices introduced into the pipe are called 'primary devices'. The term primary device also

includes the pressure tappings. All other instruments or devices required for the measurement are

known as 'secondary devices'. ISO 5167 covers primary devices; secondary devices are mentioned

only occasionally.
ISO 5167 is divided into the following six parts.

a) Part 1 gives general terms and definitions, symbols, principles and requirements as well as

methods of measurement and uncertainty that are to be used in conjunction with Part 2 to Part 6 of

ISO 5167.

b) Part 2 specifies requirements for orifice plates, which can be used with corner pressure tappings, D

and D/2 pressure tappings , and flange pressure tappings.

c) Part 3 specifies requirements for ISA 1932 nozzles , long radius nozzles and Venturi nozzles, which

differ in shape and in the position of the pressure tappings.
d) Part 4 specifies requirements for classical Venturi tubes .

e) Part 5 specifies requirements for cone meters, and includes a section on calibration.

f) Part 6 specifies requirements for wedge meters, and includes a section on calibration.

NOTE This document is complementary to ISO 5167-1:2003, ISO 5167-2:2003, ISO 5167-3:2003,

ISO 5167-4:2003 and ISO 5167-5:2015.
[1] [4]
1) See ISO 2186 and also ISO/TR 9464 .

2) Orifice plates with 'vena contracta' pressure tappings are not considered in ISO 5167.

3) ISA is the abbreviation for the International Federation of the National Standardizing Associations, which was

succeeded by ISO in 1946.

4) In the USA the classical Venturi tube is sometimes called the Herschel Venturi tube.

© ISO 2019 – All rights reserved v
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SIST EN ISO 5167-6:2019
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SIST EN ISO 5167-6:2019
INTERNATIONAL STANDARD ISO 5167-6:2019(E)
Measurement of fluid flow by means of pressure
differential devices inserted in circular cross-section
conduits running full —
Part 6:
Wedge meters
1 Scope

This document specifies the geometry and method of use (installation and operating conditions) of

wedge meters when they are inserted in a conduit running full to determine the flow rate of the fluid

flowing in the conduit.

NOTE 1 As the uncertainty of an uncalibrated wedge meter can be too large for a particular application, it

could be deemed essential to calibrate the flow meter according to Clause 7.

This document gives requirements for calibration which, if applied, are for use over the calibrated

Reynolds number range. Clause 7 could also be useful guidance for calibration of meters of similar

design but which fall outside the scope of this document.

It also provides background information for calculating the flow rate and is applicable in conjunction

with the requirements given in ISO 5167-1.

This document is applicable only to wedge meters in which the flow remains subsonic throughout

the measuring section and where the fluid can be considered as single-phase. Uncalibrated wedge

meters can only be used within specified limits of pipe size, roughness, beta (or wedge ratio) and

Reynolds number. It is not applicable to the measurement of pulsating flow. It does not cover the use of

uncalibrated wedge meters in pipes whose internal diameter is less than 50 mm or more than 600 mm,

or where the pipe Reynolds numbers are below 1 × 10 .

NOTE 2 A wedge meter has a primary element which consists of a wedge-shaped restriction of a specific

geometry. Alternative designs of wedge meters are available; however, at the time of writing there is insufficient

data to fully characterize these devices, and therefore these meters are calibrated in accordance with Clause 7.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 4006, Measurement of fluid flow in closed conduits — Vocabulary and symbols

ISO 5167-1, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 1: General principles and requirements

ISO 5168, Measurement of fluid flow — Procedures for the evaluation of uncertainties

ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories

ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in

measurement (GUM: 1995)
© ISO 2019 – All rights reserved 1
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(E)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 4006, ISO 5167-1 and the

following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
wedge gap

maximum gap between the apex of the wedge element and the pipe wall, in the plane perpendicular to

the pipe axis
Note 1 to entry: See Figure 1.
3.2
wedge ratio
ratio of the wedge gap to the meter inlet diameter, D
Note 1 to entry: See ISO 4006:1991, Clause 2, for the meter inlet diameter, D.
3.3
wedge throat area
minimum cross-sectional open area of the wedge meter
4 Principles of the method of measurement and computation

The principle of the method of measurement is based on the installation of the wedge meter into a

pipeline in which a fluid is running full. Flow through a wedge meter produces a differential pressure

between the upstream and downstream tappings.
The mass flow rate can be determined by the following formulae:
C π
q = εβDp2Δ ρ (1)
m 1
1−β
and
β = (2)

A larger β corresponds to a larger wedge gap height, h (see Figure 1), and therefore a larger throat area

A . The value of β can be calculated using Formula (3):
 2 
1  2h  2h h  h 
 
β =−arccos 1 −−21 ×− (3)
     
 
π D D D D
     
 

NOTE For example, h/D = 0,5 does not correspond to β = 0,5, but to β = √0,5 ≈ 0,707. β = 0,5 corresponds to

h/D ≈ 0,298.
2 © ISO 2019 – All rights reserved
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(E)
Key
Flow.
Figure 1 — Wedge meter showing different values of wedge ratio

The uncertainty limits can be calculated using the procedure given in ISO 5167-1:2003, Clause 8.

Similarly, the value of the volume flow rate can be calculated since
q = (4)

where ρ is the fluid density at the temperature and pressure for which the volume is stated.

Computation of the flow rate, which is a purely arithmetic process, is performed by replacing the

different items on the right-hand side of Formula (1) by their numerical values. Formula (5) (or the

computed values in Table A.1) gives wedge meter expansibility factors (ε). The values in Table A.1 are

not intended for precise interpolation. Extrapolation is not permitted. However, for a meter calibrated

according to Clause 7, the coefficient of discharge, C, is generally related to the Reynolds number, Re,

which is itself related to q , and has to be obtained by iteration (see ISO 5167-1:2003, Annex A, for

guidance regarding the choice of iteration procedure and initial estimates).

The wedge gap, h, and the pipe diameter, D, mentioned in Formula (3) are the values of the lengths at

working conditions. Measurements taken at any other conditions should be corrected for any possible

expansion or contraction of the primary device and the pipe due to the values of the temperature and

pressure of the fluid during the measurement.

As the wedge meter flow rate calculation is particularly sensitive to the pipe diameter and wedge

gap values used, the user shall ensure that these are correctly entered into the flow computation

calculations. The measured internal diameter shall be used rather than a nominal value.

It is necessary to know the density and the viscosity of the fluid at working conditions. In the case

of a compressible fluid, it is also necessary to know the isentropic exponent of the fluid at working

conditions.

NOTE The turndown of all differential pressure flow meters is dependent upon the differential pressure

range. Typically a 10:1 turndown in flow rate (equivalent to 100:1 turndown in differential pressure) can be

achieved.
5 Wedge meters
5.1 Field of application

Uncalibrated wedge meters can be used in pipes with diameters between 50 mm and 600 mm and with

0,377 ≤ β ≤ 0,791 (wedge ratio 0,2 ≤ h/D ≤ 0,6). Wedge meters with β > 0,791 (h/D > 0,6) or β < 0,377

(h/D < 0,2) are not normally manufactured.
© ISO 2019 – All rights reserved 3
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(E)

There are limits to the roughness which are addressed in 5.2.3, 5.2.7, and 6.3.2. There are limits to the

Reynolds number which are addressed in 5.5.2.
5.2 General shape

5.2.1 The wedge meter as shown in Figure 2 comprises (listed in the direction of flow) an entrance

cylinder, an upstream pressure tapping, a pipe section including the wedge element, a downstream

pressure tapping, and an exit cylinder. The form of the pressure tappings is described in 5.4.

5.2.2 The diameter D shall be measured at the plane of the upstream tapping. The number of

measurements shall be a minimum of four equally spaced around the pipe internal circumference. The

arithmetic mean value of these measurements shall be taken as the value of D in the calculations.

The minimum entrance cylinder length shall be 0,5D. The minimum exit cylinder length shall be 0,5D.

Diameters shall also be measured in planes other than the plane of the upstream pressure tapping.

No diameter along the wedge meter shall differ by more than 0,4 % from the value of the mean diameter.

This requirement is satisfied when the difference in the length of any of the measured diameters

complies with the said requirement with respect to the mean of the measured diameters.

Key
1 meter body
2 meter body centreline
3 wedge element
4 wedge apex
5 high pressure tapping
6 low pressure tapping
Flow.
Figure 2 — Geometric profile of wedge meter

5.2.3 The internal surface of the pipe section from the planes of the upstream and downstream

tappings shall be clean and smooth, and the roughness criterion, Ra, should be as small as possible and

shall be less than 10 D.

5.2.4 The wedge plane angle, θ , shall be 90° ± 2° at all points of intersection along the span of the

wedge apex. The span of the wedge apex shall be perpendicular to the centreline of the tappings and also

to the centreline of the wedge meter.
4 © ISO 2019 – All rights reserved
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SIST EN ISO 5167-6:2019
ISO 5167-6:2019(E)

5.2.5 The radius of curvature of the wedge apex, R , as shown in Figure 3, shall be less than or equal to

1 mm along the span of the wedge apex.
Figure 3 — Radius of curvature, R , at the wedge apex

5.2.6 The upstream external angle, θ , and downstream external angle, θ , of the wedge shall be

1 2
measured and shall both be equal to 135° ± 2°.

5.2.7 The wedge surface shall be clean and smooth, and the roughness criterion, Ra, shall be as small

as possible and shall always be less than 10 D.

5.2.8 Where the wedge is attached to the meter body by welding, the manufacturer should take care to

minimize the size of the weld beads within the limits required for structural integrity.

5.2.9 Where the wedge is attached to the meter body by welding, the manufacturer shall ensure there

is no intrusion of the weld into the design throat area.
5.3 Material and manufacture

5.3.1 The wedge meter may be manufactured from any material and using any construction technique,

provided that the wedge meter is in accordance with the foregoing description and will remain so

during use.

5.3.2 Hollow wedge element designs shall include a pressure equalization system to ensure the

structural stability of the wedge under rapid pressure changes.
5.4 Pressure tapping
...

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