kSIST FprEN 17694-2:2022

Hydrometry - Minimum performance requirements and test procedures for water monitoring equipment - Devices for the determination of flow - Part 2: Closed conduit instrumentation

This European standard specifies general requirements, minimum performance requirements and test procedures forinstrumentation used to measure either volumetric flow-rate and/or total volume passed of water in closed conduits. It covers all closed conduit instrument (CCI) technologies intended to operate in closed pressurised pipes and partially filled pipes.
It is recognised that for some CCIs certain tests cannot be carried out.
The data obtained from the testing of CCIs in accordance with the requirements of the Measuring Instruments Directive [4] or ISO4064-1 [5] can be used to meet, in part, the requirements specified in this European Standard. However, for the avoidance of doubt,compliance with the requirements of this European Standard does not equate to compliance with the requirements of theMeasuring Instruments Directive or ISO 4064-1.

Hydrometrie - Leistungsanforderungen und Prüfverfahren für Wasserüberwachungsgeräte - Geräte zur Bestimmung des Durchflusses - Teil 2: Messgeräte für geschlossene Rohrleitungen

Dieses Dokument legt allgemeine Anforderungen, Mindest-Leistungsanforderungen und Prüfverfahren für Messgeräte fest, die für die Messung des Volumenstroms und/oder des Gesamtdurchflussvolumens von Wasser in geschlossenen Rohrleitungen verwendet werden. Es deckt alle Technologien für Messgeräte für geschlossene Rohrleitungen (CCIs) ab, die für den Betrieb in geschlossenen Druckleitungen und teilgefüllten Rohren vorgesehen sind. Die Anforderungen werden als Volumeneinheiten angegeben, die anhand der Flüssigkeitsdichte in eine Masse umgerechnet werden können.
Es ist bekannt, dass bestimmte Prüfungen für einige CCIs nicht durchgeführt werden können.
Die bei der Prüfung von CCIs in Übereinstimmung mit den Anforderungen der Messgeräterichtlinie [1] oder den Anforderungen nach EN ISO 4064-1 [2] gewonnenen Daten können teilweise verwendet werden, um die Einhaltung der in diesem Dokument festgelegten Anforderungen nachzuweisen. Zur Klarstellung wird jedoch darauf hingewiesen, dass die Einhaltung der Anforderungen dieses Dokuments nicht mit der Einhaltung der Anforderungen der Messgeräterichtlinie oder der Anforderungen nach EN ISO 4064-1 gleichgesetzt werden kann.

Hydrométrie - Exigences de performance et modes opératoires d'essai pour les équipements de surveillance de l'eau - Dispositifs de mesure de l'écoulement - Partie 2 : Instruments de mesure pour écoulements en conduite fermée

Le présent document spécifie les exigences générales, les exigences minimales de performance et les modes opératoires d'essai applicables aux instruments utilisés pour mesurer le débit volumétrique et/ou le volume total passé d'eau dans les conduites fermées. Il couvre toutes les technologies d'instruments de mesure pour écoulements en conduite fermée (CCI) destinées à fonctionner dans des tuyaux sous pression fermés et des tuyaux partiellement remplis. Les exigences sont exprimées en unités volumétriques qui peuvent être converties en masse à l'aide de la densité de l'eau.
Il est reconnu que certains essais ne peuvent pas être effectués sur certains CCI.
Les données obtenues à partir des essais des CCI conformément aux exigences de la Directive Instruments de mesure [1] ou de l'EN ISO 4064-1 [2] peuvent être utilisées pour répondre, en partie, aux exigences spécifiées dans le présent document. Toutefois, pour éviter tout doute, le respect des exigences du présent document n'équivaut pas au respect des exigences de la Directive Instruments de mesure ou de l'EN ISO 4064-1.

Hidrometrija - Minimalne zahteve za tehnične lastnosti in preskusni postopki za opremo za nadzor vode - Naprave za ugotavljanje pretoka - 2. del: Instrumenti za merjenje v zaprtem vodu

General Information

• Status: Not Published
• Public Enquiry End Date: 31-Oct-2021
• ICS: 07.060 - Geology. Meteorology. Hydrology
• ICS: 17.120.10 - Flow in closed conduits
• Technical Committee: IMIN - Measurement instruments
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 23-Nov-2022
• Due Date: 11-Jan-2023
• Completion Date: 24-Nov-2022
• Directive: 2000/60/EC - Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy (substitutes Directive Reference 01/991 - Common Position on WFD)
• Ref Project: FprEN 17694-2 - Hydrometry - Minimum performance requirements and test procedures for water monitoring equipment - Devices for the determination of flow - Part 2: Closed conduit instrumentation

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN 17694-2:2021
01-oktober-2021
Hidrometrija - Zahteve za tehnične lastnosti in preskusni postopki za opremo za

nadzor vode - Naprave za ugotavljanje pretoka - 2. del: Instrumenti za merjenje v

zaprtem vodu
Hydrometry - Performance requirements and test procedures for water monitoring

equipment - Devices for the determination of flow Part 2: Closed conduit instrumentation

Hydrometrie - Leistungsanforderungen und Prüfverfahren für
Wasserüberwachungsgeräte - Geräte zur Bestimmung des Durchflusses - Teil 2:
Messgeräte für geschlossene Rohrleitungen
Ta slovenski standard je istoveten z: prEN 17694-2
ICS:
07.060 Geologija. Meteorologija. Geology. Meteorology.
Hidrologija Hydrology
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
oSIST prEN 17694-2:2021 en

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

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oSIST prEN 17694-2:2021
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oSIST prEN 17694-2:2021
DRAFT
EUROPEAN STANDARD
prEN 17964-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2021
ICS 07.060; 17.120.20
English Version
Hydrometry - Performance requirements and test
procedures for water monitoring equipment - Devices for
the determination of flow Part 2: Closed conduit
instrumentation
Hydrometrie - Leistungsanforderungen und
Prüfverfahren für Wasserüberwachungsgeräte - Geräte
zur Bestimmung des Durchflusses - Teil 2: Messgeräte
für geschlossene Rohrleitungen

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/TC 318.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17964-2:2021 E

worldwide for CEN national Members.
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Contents Page

European foreword ............................................................................................................................ 4

Introduction ......................................................................................................................................... 5

1 Scope ......................................................................................................................................... 6

2 Normative references ......................................................................................................... 6

3 Terms and definitions ........................................................................................................ 6

4 Symbols .................................................................................................................................... 8

5 Principle .................................................................................................................................. 8

6 General requirements ........................................................................................................ 9

6.1 Requirements for closed conduit instrumentation ................................................. 9

6.2 Requirements for associated documentation .......................................................... 10

7 Performance requirements ............................................................................................ 11

7.1 Expression of performance requirements ................................................................ 11

7.2 Performance requirements ............................................................................................ 12

7.3 Data retention ..................................................................................................................... 13

7.4 Environmental requirements ........................................................................................ 14

7.5 Water temperature requirements ............................................................................... 14

7.6 Installation influences ...................................................................................................... 14

7.7 Field test requirements.................................................................................................... 14

8 Testing .................................................................................................................................... 15

8.1 General requirements for testing ................................................................................. 15

8.2 Laboratory test conditions ............................................................................................. 15

8.3 Reporting .............................................................................................................................. 17

9 Laboratory test procedures ............................................................................................ 17

9.1 Guidance for establishing a test plan .......................................................................... 17

9.2 Verification by inspection ............................................................................................... 20

9.3 Performance tests .............................................................................................................. 20

9.3.1 Loss of power for electronic CCIs.................................................................................. 20

9.3.2 Bias and repeatability....................................................................................................... 20

9.3.3 Supply voltage ..................................................................................................................... 21

9.3.4 Output impedance.............................................................................................................. 22

9.3.5 Water temperature ............................................................................................................ 22

9.3.6 Ambient air temperature and relative humidity .................................................... 22

9.3.7 Sensor location .................................................................................................................... 23

9.3.8 Presence of stray currents .............................................................................................. 24

9.3.9 Bi-directional flow ............................................................................................................. 25

9.3.10 Flow reversal ....................................................................................................................... 25

9.3.11 Ancillary devices ................................................................................................................ 25

9.3.12 Effect of conduit material ................................................................................................ 25

9.3.13 Effect of conduit size ......................................................................................................... 26

9.3.14 Fill level .................................................................................................................................. 27

9.3.15 Response time ..................................................................................................................... 27

10 Field test procedures ........................................................................................................ 28

10.1 Objective of field test ........................................................................................................ 28

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10.2 Field test plan ...................................................................................................................... 28

10.3 Field test requirements.................................................................................................... 28

10.4 Error under field test conditions .................................................................................. 29

10.5 Up-time .................................................................................................................................. 29

10.6 Maintenance ......................................................................................................................... 30

Annex A (normative) Evaluation of test data ........................................................................ 31

Annex B (Informative) Reference methods .......................................................................... 40

Annex C (Informative) Reference uncertainty and error calculations ........................ 41

Annex D (informative) Example report format .................................................................... 43

Bibliography ....................................................................................................................................... 46

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European foreword
This document (prEN 17694-2) has been prepared by Technical Committee CEN/TC 318
“Hydrometry”, the secretariat of which is held by BSI.
This document is currently submitted to the CEN Enquiry.
This standard is published in two parts:

prEN 17694-1 Hydrometry - Performance requirements and test procedures for water monitoring

equipment – Devices for the determination of flow - Part 1 Open channel instrumentation

prEN 17694-2 Hydrometry - Performance requirements and test procedures for water monitoring

equipment – Devices for the determination of flow - Part 2 Closed conduit instrumentation

This document has been prepared under a Standardization Request given to CEN by the

European Commission and the European Free Trade Association.
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Introduction

This document is a product standard for instrumentation for the determination of the flow of

waters in closed conduits (e.g. effluent discharges from industrial installations, and wastewaters

from sewage treatment works, water irrigation channels and water transfer channels). A closed

conduit instrument (CCI) is a device that is normally fixed in position and used mainly to

measure either volumetric flow-rate and/or total volume passed. Certain CCI, e.g. Coriolis

devices measure mass flow-rate and/or total mass passed, from which volumetric flow may be

derived, using the density of the fluid. This document defines general requirements, minimum

performance requirements, and test procedures. A CCI that is shown, by means of the tests, to

conform with the general requirements and performance requirements is considered to be fit

for purpose. However, this document does not cover the installation and on-going use of a CCI,

and also excludes instrumentation that is subject to separate legal control, for example, the

Measuring Instruments Directive.

The acronym “CCI” is used throughout this document except where it is necessary to be specific

about the particular type or component (e.g. sensor) of a device.

The general requirements and performance requirements specified in this document are

intended to be independent of measurement technology and applicable to all CCIs. The general

requirements include several features that are necessary to meet users’ applications and

information that should be included in associated documents.

The performance tests comprise testing carried out under laboratory and field conditions. They

are designed to determine, in a systematic and consistent way, the capability of CCI to make

reliable measurements. The testing focuses on key performance characteristics. Statistical

procedures are defined for evaluation of the test data.

Measurement ranges are not specified as part of the performance requirements though a

minimum ratio (maximum measured value: minimum measured value) is specified. It is for the

manufacturer of the CCI to decide on the measurement range over which the performance

requirements are shown to be met by the specified test procedures. Similarly, it is for the CCI

manufacturer to decide on the intended uses (applications) which will inform the design of the

field trial.

Water monitoring equipment is widely used for compliance monitoring purposes under

national and European regulations.
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1 Scope

This document specifies general requirements, minimum performance requirements and test

procedures for instrumentation used to measure either volumetric flow-rate and/or total

volume passed of water in closed conduits. It covers all closed conduit instrument (CCI)

technologies intended to operate in closed pressurized pipes and partially filled pipes.

Requirements are expressed in volumetric units which may be converted to mass using the fluid

density.
It is recognized that for some CCIs certain tests cannot be carried out.

The data obtained from the testing of CCIs in accordance with the requirements of the Measuring

Instruments Directive [1] or EN ISO 4064-1 [2] can be used to meet, in part, the requirements

specified in this document. However, for the avoidance of doubt, compliance with the

requirements of this document does not equate to compliance with the requirements of the

Measuring Instruments Directive or EN ISO 4064-1.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document the following terms and definitions apply.

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

addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
combined performance requirement
combination of individual performance requirements
3.2
conduit
pipe through which water is flowing
3.3
closed conduit instrument
CCI

device(s) which measures the flow-rate or totalized volume of water passing along a conduit or

computes such quantities from measurements of one or more properties which have a defined

relationship with the flow-rate

Note to 1 entry: A closed conduit instrument can, for example, include a complete flow-metering system,

such as: a flow sensor and transmitter, a mechanical CCI including any ancillary device required to derive

an electronic output, a velocity-area CCI comprising a water velocity sensor with a water level sensor,

associated electronics and flow computer, a bespoke gauge with a water level sensor, associated

electronics and flow computer, a non-standardized primary device with a differential pressure sensor,

associated electronics and flow computer.
3.4
determinand
the property that is required to be measured
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3.5
expanded uncertainty

expanded measurement uncertainty product of a combined measurement uncertainty and a

factor larger than the number one

Note 1 to entry: The factor depends upon the type of probability distribution of the output quantity in a

measurement model and on the selected coverage probability.

Note 2 to entry: The term “factor” in this definition refers to a coverage factor.

Note 3 to entry: Expanded measurement uncertainty is termed “overall uncertainty” in paragraph 5 of

Recommendation INC-1 (1980) (see the GUM) and simply “uncertainty” in IEC documents.

[ISO/IEC Guide 99:2007, 2.35 plus notes]
3.6
flow-rate
volume of water passing through the CCI per unit time
3.7
influence quantity

any quantity, generally external to the CCI, which may affect the performance of the equipment

3.8
measurement range

range over which the CCI conforms within the performance requirements specified in this

document

Note to 1 entry: The measurement range is defined from a minimum non-zero value to a maximum value.

3.9
non-invasive sensor

sensor for application to a pipe which attaches to the outside of a pipe and requires no tapping,

drilling or cutting of the pipe to install, for example clamp-on ultrasonic transducers

3.10
percentage error
error in measurement expressed as a percentage of the true or actual value

Note to 1 entry: In this document, the true or actual value is the reference value and percentage error is

calculated using the following equation: percentage error = 100 X (measured value – reference

value)/reference value.
3.11
performance requirement

one of the quantities (described by values, tolerances, range) that defines a CCI’s performance

3.12
rated operating conditions

minimum to maximum values of any environmental, fluid or electrical parameter within which

a CCI is designed to operate without adjustment, within the performance requirements specified

in this document
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3.13
reference conditions

specified set of values (including tolerances) of influence variables, delivering representative

values of performance requirements
3.14
reference method

method to be used to obtain the determinand value to a stated uncertainty, against which the

readings from the CCI under test can be compared
3.15
repeatability

ability of a CCI to provide closely similar indications for repeated applications of the same

determinand under the same conditions of measurement
3.16
sensor

transducer consisting of one or more components from which is derived an electrical or

mechanical output related to a property from which the flow-rate may be computed
3.17
totalized volume

the total volume of water which has been measured by the CCI over a period of time which

commenced when the totalizer was set to zero
4 Symbols
For the purposes of this standard the following symbols apply.
b Bias
S Repeatability
X Errors due to variations in supply voltage
Errors due to variations in output impedance
Errors due to variations in fluid temperature
X Errors due to variations in ambient air temperature
X Errors due to variations in relative humidity
X Errors due to variations in sensor location
Errors due to variations in stray currents
Combined performance requirement
5 Principle

This document sets general requirements, minimum performance requirements and test

procedures for a CCI that is to be used for determining the flow of water in closed conduits.

The general requirements are based on experience of users’ needs when operating a CCI in a

range of applications. Many are consistent with general requirements specified in

EN ISO 4064-1.
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The minimum performance requirements specify limit values in terms of percentage error for

measurement bias, repeatability, a range of environmental and sensor operational parameters,

and for a combination of all of these values. A CCI that can be demonstrated by the specified tests

to conform with the performance requirements is judged to be fit for purpose.

For the majority of applications where CCI are used, the required parameter is volumetric flow-

rate.

In Table 2 the combined performance requirement is less than the sum of the specified

individual performance values combined in quadrature. This allows for some differences in

performance of CCIs with respect to the individual requirements within an overall combined

performance requirement.

The laboratory performance tests are designed to show whether a CCI can conform with the

applicable performance requirements under a range of environmental and sensor operational

conditions. Laboratory testing is used to determine the performance characteristics in a

systematic and consistent way in a controlled environment. Several of the laboratory tests

correspond to tests specified in EN ISO 4064-2 [3] and ISO 12242 [4]. For CCI that are tested to

demonstrate conformity with EN ISO 4064 and ISO 12242 the test data can also be used for the

purposes of this document thereby minimizing the amount of testing.

Statistical procedures are defined for evaluation of the laboratory test data to produce the

individual performance characteristic measurement uncertainties, u, and the combined

performance characteristic measurement uncertainty, U . They are based on the

ISO/IEC Guide 98-3 [5]. The measured errors arising from the tests for each performance tests

are converted to standard uncertainties, taking into account the probable distribution of errors.

To obtain the combined performance characteristic, the individual uncertainties are combined

using a root sum of squares, as described in the GUM, with due account taken of the contribution

of each component through the use of sensitivity coefficients. To determine sensitivity

coefficients, it is necessary to know the functions by which each component contributes to

overall error. In the case of CCI testing this will rarely be known. Hence for the purposes of this

standard, the sensitivity coefficients are all taken as 1.

The combined performance characteristic, U , is expressed as an expanded uncertainty. The

expanded uncertainty, (U), is obtained by multiplying the standard uncertainty by a coverage

factor. The coverage factor is determined by the confidence level. This document uses a 95 %

confidence with a coverage factor assumed to be 2.

The field trial is used to demonstrate that the performance of a CCI can be maintained under

operational conditions and to determine the CCI’s up-time.
6 General requirements
6.1 Requirements for closed conduit instrumentation
A CCI shall have:

a) an unique designation that unambiguously identifies the CCI (e.g. model, serial number);

b) a means of protection against inadvertent or unauthorized access to the control functions

(e.g. password, physical locks, etc);

c) an output signal and/or display scaled in metric units (the units of measurement shall be

displayed on the indicating device);
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d) one or more output signals and/or a means of displaying the measured determinand and/or

either the totalized volume and / or volumetric flow-rate. If the CCI does not incorporate a

local display, it shall be possible for an authorized person to obtain the current reading by

communicating with the CCI on site using a portable device, such as a laptop, tablet or smart

phone. Communication with a portable device to display a reading shall not interrupt the

measurement.

e) a means of displaying its operating status, for example, normal operation, stand-by,

maintenance mode or malfunction;

f) an audible or visual method of indicating loss of power supply (applies only to CCI operating

from an external power supply), e.g. a relay that fails open;

g) an audible or visual method of indicating when the power supply voltage is below its normal

operating limit (applies only to CCIs operating from a battery);

h) a means for preventing unauthorized resetting of the total recorded volume for abstraction

metering and / or effluent discharge monitoring; a symbol, incorporated into the indication

device to show the flow direction, for bi-directional CCI;

NOTE A pointer rotating clockwise with increasing flow and counter-clockwise with reverse

flow is acceptable but reliance on an increasing or decreasing total is not.

i) a clear marking of the direction of forward flow (in the case of a bi-directional CCI this

should be the direction of flow which gives an increase in the total flow recorded. For a CCI

which has been wet calibrated, this should be the direction of flow in which the CCI has been

calibrated);

j) a means to subtract from the indicated volume or to record separately the reverse flow

volume, for a bi-directional CCI;

k) an upstream strainer or filter to protect the CCI, where recommended by the manufacturer;

-1 -

l) a minimum rated operating range for fluid conductivity between 50 μS cm to 1200 μS cm

for an electro-magnetic device.
6.2 Requirements for associated documentation

The following information shall be incorporated into the associated documentation:

a) operating instructions which cover the full functionality and measurement principle of the

CCI;

b) generic guidance on the time period over which the CCI can operate continuously without

requiring manual adjustment or intervention;

NOTE 1 Automatic routines for cleaning, maintenance or recalibration can be used to maintain

performance within the required limits between manual interventions. It is up to the user to ensure

that a suitable regime is adopted for an individual application.

c) a statement of the types of primary device, where applicable, for which the CCI can compute

flow-rate without the input of data other than the type and dimensions of the structure and

a zero datum;

d) a statement of whether the CCI is designed to measure flow in both forward and

reverse directions;
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e) a statement defining minimum up and downstream straight lengths of conduit of uniform

section adjacent to the sensor required to meet the performance requirements of this

document;

f) a statement of any limitations on the material of conduit into or onto which the CCI’s sensor

can be installed;

g) a statement of any limitations on the conduit dimensions or shape (including wall thickness

or pipe schedule if appropriate), into or onto which the CCI’s sensor can be installed. If

multiple sensors are required, for example in a large conduit, the number and spacing of

those sensors shall be stated;

h) for non-contact velocity sensors, a statement of the minimum and maximum separation

distances from the sensor face to the fluid surface;

i) a statement of the minimum measurable fluid depth under free surface conditions (the

maximum measurable fluid depth is assumed to be full bore), for CCIs intended to operate

in partially filled pipes. The manufacturer shall also state whether the CCI can maintain

performance within the requirements of this document under surcharged conditions. A CCI

that can only operate in partially filled pipe with free surface conditions should be tested in

accordance with EN 17694-1 [6];

j) a statement, where appropriate, of the rated operating conditions for water pressure;

k) a statement of the quality (e.g. contaminants, salinity) nature and quantity of particulate or

other material that the CCI can pass whilst maintaining its performance within the limits of

this standard. If a minimum level of particulate is required for operation of the CCI, this too

shall be stated;

l) a statement of any specific requirements relating to the location or shielding of components

necessary to maintain performance within the limits of this standard under varying

environmental conditions

m) a statement, for electronic CCI, of the rated operating conditions for the power supply;

n) a statement, for electronic CCI, of the rated operating conditions for the signal load

impedance on the analogue output, if present;

o) a statement of the rated operating conditions for water temperature, ambient temperature

and humidity as appropriate;

NOTE 2 The influence of ambient temperature and relative humidity on the performance of a CCI

is tested (see 7.4 and 9.3.6) over the rated environmental operating conditions.

p) the minimum rated operating range for fluid conductivity for an electromagnetic CCI.

7 Performance requirements
7.1 Expression of performance requirements

Specific requirements are expressed as bias (b), variations in error (X), standard deviation (u)

or expanded uncertainty (U) as shown in Table 1. Not all requirements will apply to every CCI

Annex A describes in detail how the values are calculated for each requirement.
...