Measurement of fluid flow in closed conduits — Thermal mass flowmeters

This document gives guidelines for the specification, testing, inspection, installation, operation and calibration of thermal mass gas flowmeters for the metering of gases and gas mixtures. It is not applicable to measuring liquid mass flowrates using thermal mass flowmeters. This document is not applicable to hot wire and other hot film anemometers, also used in making point velocity measurements.

Mesure de débit des fluides dans les conduites fermées — Débitmètres massiques par effet thermique

General Information

Status
Published
Publication Date
09-Jan-2019
Current Stage
6060 - International Standard published
Start Date
10-Jan-2019
Completion Date
10-Jan-2019
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INTERNATIONAL ISO
STANDARD 14511
Second edition
2019-01
Measurement of fluid flow in closed
conduits — Thermal mass flowmeters
Mesure de débit des fluides dans les conduites fermées — Débitmètres
massiques par effet thermique
Reference number
ISO 14511:2019(E)
ISO 2019
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ISO 14511:2019(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

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Published in Switzerland
ii © ISO 2019 – All rights reserved
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ISO 14511:2019(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

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

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

3 Terms and definitions ..................................................................................................................................................................................... 1

3.1 General terms ........................................................................................................................................................................................... 1

3.2 Specific terms ........................................................................................................................................................................................... 2

4 Selection of thermal mass flowmeters .......................................................................................................................................... 4

5 Capillary thermal mass flowmeter (CTMF meter) ............................................................................................................. 5

5.1 Principles of measurement .......................................................................................................................................................... 5

5.2 Typical design .......................................................................................................................................................................................... 8

5.3 Applications and limitations of use ....................................................................................................................................... 8

5.3.1 Gas property effects ...................................................................................................................................................... 8

5.3.2 Application and fluid properties ........................................................................................................................ 9

5.3.3 Temperature effects ...................................................................................................................................................... 9

5.3.4 Pressure effects ................................................................................................................................................................. 9

5.3.5 Pulsation effects ............................................................................................................................................................... 9

5.3.6 Pressure loss ........................................................................................................................................................................ 9

5.3.7 Cleanness of the gas ...................................................................................................................................................... 9

5.3.8 Mounting orientation effects ................................................................................................................................. 9

5.3.9 Installation effects for flow profile ................................................................................................................10

5.3.10 Vibrations — Hydraulic and mechanical .................................................................................................10

5.3.11 Valves ......................................................................................................................................................................................10

5.4 Meter selection ....................................................................................................................................................................................10

5.4.1 Principal requirement ..............................................................................................................................................10

5.4.2 Performance specifications .................................................................................................................................10

5.4.3 Physical specifications .............................................................................................................................................10

5.4.4 Meter ratings ....................................................................................................................................................................11

5.4.5 Application and fluid properties .....................................................................................................................11

5.4.6 Corrosion .............................................................................................................................................................................11

5.4.7 Transmitter specifications ....................................................................................................................................11

5.5 Installation and commissioning ............................................................................................................................................11

5.5.1 General considerations ............................................................................................................................................11

5.5.2 Safety .......................................................................................................................................................................................12

5.5.3 Mechanical stress .........................................................................................................................................................12

5.5.4 Process adjustment ....................................................................................................................................................12

6 Insertion and/or in-line thermal mass flowmeter (ITMF meter) ..................................................................13

6.1 Principle of measurement ..........................................................................................................................................................13

6.1.1 General...................................................................................................................................................................................13

6.1.2 Constant power method .........................................................................................................................................14

6.1.3 Constant-temperature-differential method ..........................................................................................15

6.2 Typical design .......................................................................................................................................................................................16

6.2.1 ITMF basic design ........................................................................................................................................................16

6.2.2 In-line ITMF meter ......................................................................................................................................................16

6.2.3 Insertion-ITMF meter ...............................................................................................................................................17

6.2.4 Multi-point insertion-ITMF meter .................................................................................................................18

6.3 Applications and limitations of use ....................................................................................................................................18

6.3.1 General remarks ............................................................................................................................................................18

6.3.2 Normalized volume flowrate units................................................................................................................18

6.3.3 Fluid property effects ...............................................................................................................................................18

6.3.4 Temperature effects ...................................................................................................................................................19

6.3.5 Pressure effects ..............................................................................................................................................................19

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ISO 14511:2019(E)

6.3.6 Fluid phase .........................................................................................................................................................................19

6.3.7 Bi-directional flow .......................................................................................................................................................19

6.3.8 Pulsation effects ............................................................................................................................................................19

6.3.9 Pressure loss .....................................................................................................................................................................19

6.3.10 Sensor contamination ..............................................................................................................................................19

6.3.11 Mounting orientation effects ..............................................................................................................................19

6.3.12 Installation effects .......................................................................................................................................................20

6.3.13 Conduit vibrations .......................................................................................................................................................20

6.4 Meter selection ....................................................................................................................................................................................20

6.4.1 General...................................................................................................................................................................................20

6.4.2 Performance specifications .................................................................................................................................20

6.4.3 Physical specifications .............................................................................................................................................21

6.4.4 Meter ratings ....................................................................................................................................................................21

6.4.5 Application and fluid properties .....................................................................................................................21

6.4.6 Corrosion .............................................................................................................................................................................22

6.4.7 Transmitter specifications ....................................................................................................................................22

6.5 Installation and commissioning ............................................................................................................................................22

6.5.1 General considerations ............................................................................................................................................22

6.5.2 Cleaning ................................................................................................................................................................................22

6.5.3 Safety .......................................................................................................................................................................................22

6.5.4 Mechanical stress .........................................................................................................................................................23

6.5.5 Process conditions ......................................................................................................................................................24

7 Instrument specification sheet and marking ......................................................................................................................24

7.1 User specification sheet ...............................................................................................................................................................24

7.2 Manufacturer's data sheet ......... .................................................................................................................................................24

7.3 Marking ......................................................................................................................................................................................................25

7.3.1 Mandatory ..........................................................................................................................................................................25

7.3.2 Optional ................................................................................................................................................................................26

8 Calibration ...............................................................................................................................................................................................................26

8.1 General considerations .................................................................................................................................................................26

8.2 Use of the desired gas under process conditions ...................................................................................................27

8.3 Use of a surrogate gas ....................................................................................................................................................................27

8.4 In situ calibration ..............................................................................................................................................................................27

8.5 Insertion-ITMF meter ....................................................................................................................................................................27

8.6 Calibration frequency .....................................................................................................................................................................27

8.7 Calibration certificate .....................................................................................................................................................................27

9 Pre-installation inspection and testing .....................................................................................................................................28

10 Maintenance ...........................................................................................................................................................................................................28

10.1 General ........................................................................................................................................................................................................28

10.2 Visual inspection ................................................................................................................................................................................29

10.3 Functional test ......................................................................................................................................................................................29

10.4 Record keeping (Maintenance audit trail) ...................................................................................................................29

Bibliography .............................................................................................................................................................................................................................30

iv © ISO 2019 – All rights reserved
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ISO 14511:2019(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 of 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 www .iso

.org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed

conduits, Subcommittee SC 5, Velocity and mass methods.

This second edition cancels and replaces the first edition (ISO 14511:2001), of which it constitutes a

minor revision.
The changes compared to the previous edition are as follows:

— the sentence “The measurand temperature difference between the two sensors is proportional to the

mass flow rate” has been removed from 5.1;
— the references to the VIM and GUM Guides have been updated.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
© ISO 2019 – All rights reserved v
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ISO 14511:2019(E)
Introduction

This document has been prepared to guide those concerned with the specification, testing, inspection,

installation, operation and calibration of thermal mass gas flowmeters.
A list of standards related to this document is given in the Bibliography.
vi © ISO 2019 – All rights reserved
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INTERNATIONAL STANDARD ISO 14511:2019(E)
Measurement of fluid flow in closed conduits — Thermal
mass flowmeters
1 Scope

This document gives guidelines for the specification, testing, inspection, installation, operation

and calibration of thermal mass gas flowmeters for the metering of gases and gas mixtures. It is not

applicable to measuring liquid mass flowrates using thermal mass flowmeters.

This document is not applicable to hot wire and other hot film anemometers, also used in making point

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

measurement (GUM: 1995)
ISO 4006, Measurement of fluid flow in closed conduits — Vocabulary and symbols

ISO 7066-2, Assessment of uncertainty in the calibration and use of flow measurement devices — Part 2:

Non-linear calibration relationships

IEC 61000-4, Electromagnetic compatibility (EMC) — Part 4: Testing and measurement techniques

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 4006 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 General terms
3.1.1
flowrate

quotient of the quantity of fluid passing through the cross-section of a conduit and the time taken for

this quantity to pass through this section

Note 1 to entry: In this International Standard, the term “flowrate” is used as a synonym for mass flowrate,

unless otherwise stated.
3.1.2
mass flowrate
flowrate in which the quantity of fluid is expressed as a mass

Note 1 to entry: The term “flowrate” is used as a synonym for mass flowrate in this International Standard,

unless otherwise stated.
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ISO 14511:2019(E)
3.1.3
uncertainty of measurement

parameter, associated with the result of a measurement, that characterizes the dispersion of the values

that can reasonably be attributed to the measurand

Note 1 to entry: To explain the closeness of agreement between the result of a measurement and a true value of

the measurand the expression “accuracy of measurement” is used.
Note 2 to entry: Accuracy is a qualitative concept.
3.1.4
repeatability

ability of a measuring instrument to provide closely similar indications for

repeated applications of the same measurand under the same conditions of measurement

Note 1 to entry: These conditions include:
— minimized variations resulting from the observer;
— the same measurement procedure;
— the same observer;
— the same measuring equipment, used under the same conditions;
— the same location;
— repeated measurements within a short period of time.
3.1.5
flow profile
graphic representation of the velocity distribution

Note 1 to entry: The point flow velocity across the cross-section of a conduit is not constant. It varies as a

consequence of upstream and downstream disturbances and with the Reynolds number of the flow stream. For a

fully developed flow, the point flow velocity varies from 0 m/s at the pipe wall to a maximum value at the conduit

centre. The flow profile describes the variation of the flow velocity across the conduit cross-section and may be

expressed mathematically or graphically.
3.2 Specific terms
3.2.1
sensor

element of a measuring instrument or measuring chain that is directly affected by the measurand

3.2.2
laminar flow element

element inserted into the gas stream to establish a constant ratio between the main flow stream and

the bypass flow through the sensor
3.2.3
thermal mass flowmeter
TMF meter

flow-measuring device which uses heat transfer to measure and indicate mass flowrate

Note 1 to entry: The term thermal mass flowmeter also applies to the measuring portion of a thermal mass flow

controller and not the control function.
3.2.4
capillary thermal mass flowmeter
CTMF meter

TMF meter normally consisting of a laminar flow element, bypass tube (capillary), temperature sensors

(some designs include a separate heater) with supporting electronics and housing
2 © ISO 2019 – All rights reserved
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ISO 14511:2019(E)
3.2.5
insertion and/or in-line thermal mass flowmeter
ITMF meter

TMF meter normally consisting of one or two temperature sensing sensors (some designs have a

separate heater) with supporting structure, electronics and housing, of which the sensors are exposed

to the full gas stream
3.2.5.1
insertion-ITMF meter

ITMF meter with the sensors mounted on a probe, inserted through the process conduit wall, into the

gas stream
3.2.5.2
in-line ITMF meter

ITMF meter with the sensors mounted in a flow body which serves as an integral part of the conduit

3.2.6
mass flow controller

flow controlling device that comprises a TMF meter, a valve and controlling electronics

Note 1 to entry: The output of the TMF meter is compared against an adjustable setpoint and the valve is

correspondingly opened or closed to maintain the measured flowrate at the setpoint value.

3.2.7
transmitter

associated electronics providing the heater with electrical power and transforming the signals from

the temperature sensors to give output(s) of the measured parameters

Note 1 to entry: The transmitter can be integrally mounted to a TMF meter. However, for some applications the

transmitter can be remotely installed away from the flow sensor.
3.2.8
retractor mechanism

mechanical arrangement including an isolation valve that allows the

positioning and/or extraction of the flow sensor within the conduit
3.2.9
rangeability

statement of the minimum and maximum limits of which an individual sensor can measure and indicate

EXAMPLE For a maximum flowrate = 1 000 kg/h and a minimum flowrate = 10 kg/h, the

rangeability = 10 kg/h to 1 000 kg/h.
3.2.9.1
turndown

numerical ratio of the maximum to minimum limits of which an individual sensor can measure

EXAMPLE For a maximum flowrate = 1 000 kg/h and a minimum flowrate = 10 kg/h, the turndown

ratio = 1 000/10 = 100:1.

Note 1 to entry: In practice, the terms rangeability and turndown are used interchangeably and can be associated

with an uncertainty statement.
3.2.10
k-factor

numerical factor unique to each TMF meter which is associated with the mass flowrate derived during

the calibration and when programmed into the transmitter ensures that the meter performs to its

stated specification

Note 1 to entry: When a surrogate gas has been used for calibration purposes, the manufacturer’s gas factor list

or database has been applied for conversion to the desired gas under process conditions.

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ISO 14511:2019(E)
3.2.11
normalized volume flowrate, (GB)
standardized volume flowrate, (US)

flowrate for which the quantity of fluid is expressed in terms of volume, with the fluid density calculated

at a known and fixed pressure and temperature condition

Note 1 to entry: The values used to define these reference conditions (also known as “standard reference

conditions”) are industry and country specific and therefore shall always be specified when these units are used.

Typical reference conditions are 0 °C and 101,325 kPa.

Note 2 to entry: Normalized volumetric units or volumetric units specified to standard reference conditions,

such as “Nm /h”, are commonly used with CTMF and ITMF meters, h
...

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