CEN/TR 15983:2010

SLOVENSKI STANDARD
01-april-2010
(PLVLMHQHSUHPLþQLKYLURY1DYRGLOR]DXSRUDER(1
Stationary source emissions - Guidance on the application of EN 14181:2004
Emissionen aus stationären Quellen - Leitlinien zur Anwendung der EN 14181:2004
Emissions de sources fixes - Lignes directrices relatives à l'application de l'EN
14181:2004
Ta slovenski standard je istoveten z: CEN/TR 15983:2010
ICS:
13.040.40 (PLVLMHQHSUHPLþQLKYLURY Stationary source emissions
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 15983
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
January 2010
ICS 13.040.40
English Version
Stationary source emissions - Guidance on the application of EN
14181:2004
Emissions de sources fixes - Guide d'application de l'EN Emissionen aus stationären Quellen - Leitlinien zur
14181:2004 Anwendung der EN 14181:2004

This Technical Report was approved by CEN on 1 December 2009. It has been drawn up by the Technical Committee CEN/TC 264.

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, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

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© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 15983:2010: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Introduction .4
1 Scope .5
2 Terms and definitions .5
3 Symbols and abbreviations .9
3.1 Symbols .9
3.2 Abbreviations . 10
4 General guidance on quality assurance and calibration . 10
4.1 General . 10
4.2 Regulatory framework and standards for monitoring . 10
4.3 Roles and responsibilities . 12
5 Application of QAL1 . 12
5.1 General . 12
5.2 AMS which are not yet installed at the plant . 13
5.3 AMS which are already installed at the plant . 13
6 Application of QAL2 and AST . 13
6.1 Tasks within QAL2 and AST . 13
6.2 Location and monitoring provisions for AMS . 14
6.3 Management system provisions for AMS . 14
6.4 Specific issues of the functional tests . 14
7 Calibration and validation of the AMS . 16
7.1 Standard reference methods . 16
7.2 Calibration using an SRM . 16
7.3 Low-level clusters . 20
7.4 Peripheral AMS measurements . 21
7.5 Establishing the calibration function and the test of variability . 21
7.6 Data points outside the calibration range . 22
7.7 Calibrating AMS for NO and TOC . 23
x
7.8 Significant changes to operating conditions and fuels . 24
7.9 Significant changes to an AMS . 24
8 On-going surveillance and quality assurance of AMS (QAL3) . 25
8.1 The necessity for QAL3 . 25
8.2 Choosing control charts . 25
8.3 Zero and span measurements . 26
8.4 Setting parameters for control charts . 29
Annex A (informative) An example of a procedure for determining outliers . 31
Annex B (informative) Alternative approaches for dealing with low-level clusters of emissions . 34
Annex C (informative) k values . 36
v
Annex D (informative) Shewhart and EWMA control charts . 37
Bibliography . 43

Foreword
This document (CEN/TR 15983:2010) has been prepared by Technical Committee CEN/TC 264 “Air quality”,
the secretariat of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

Introduction
This CEN Technical Report provides supporting guidance on the application of EN 14181:2004. It is based on
the growing experiences with EN 14181:2004 throughout the CEN member countries. EN 14181:2004
specifies three levels of quality assurance (QAL), known as QAL1, QAL2 and QAL3 as well as an Annual
Surveillance Test (AST). This Technical Report explains the requirements of these levels of quality assurance
to achieve a consistent application of EN 14181:2004.
1 Scope
This CEN Technical Report provides guidance for applying the European Standard EN 14181:2004.
This CEN Technical Report provides guidance only on applying the quality assurance levels QAL1, QAL2 and
QAL3 as well as the Annual Surveillance Test (AST).
This CEN Technical Report is an informative document.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
air quality characteristic
one of the quantifiable properties relating to an air mass under investigation, for example, concentration of a
constituent
[EN 14181:2004, 3.1]
2.2
automated measuring system
AMS
measuring system permanently installed on site for continuous monitoring of emissions
[EN 14181:2004, 3.2]
NOTE 1 An AMS is the automated application of a monitoring method, which is traceable to a reference method.
NOTE 2 Apart from the analyser, an AMS includes facilities for taking samples (e.g. sample probe, sample gas lines,
flow meters, regulators, delivery pumps) and for sample conditioning (e.g. dust filter, moisture removal devices,
converters, diluters). This definition also includes testing and adjusting devices that are required for regular functional
checks.
2.3
calibration function
linear relationship between the values of the SRM and the AMS with the assumption of a constant residual
standard deviation
[EN 14181:2004, 3.3]
NOTE The calibration function is established during QAL2 on stack gases.
2.4
competent authority
organisation which implements the requirements of EU Directives and regulates installations, which must
comply with the requirements of applicable European Standards
[EN 15267-1:2009, 3.3]
2.5
confidence interval (two-sided)
when T and T are two functions of the observed values such that, θ being a population parameter to be
1 2
estimated, the probability P (T ≤ θ ≤ T ) is at least equal to (1 – α) [where (1 – α) is a fixed number, positive
r 1 2
and less than 1], the interval between T and T is a two-sided (1 – α) confidence interval for θ
1 2
[EN 14181:2004, 3.5]
2.6
CUSUM chart
calculation procedure in which the amount of drift and change in precision is compared to the corresponding
uncertainty components which are obtained during QAL1
[EN 14181:2004, 3.6]
2.7
drift
monotonic change of the calibration function over stated period of unattended operation, which results in a
change of the measured value
[EN 14181:2004, 3.7]
NOTE This refers to a change in the response of the AMS to a determinant which does not change.
2.8
emission limit value
ELV
limit value related to the uncertainty requirement
[EN 14181:2004, 3.8]
NOTE For EU Directives it is the daily emission limit value that relates to the uncertainty requirement.
2.9
extractive AMS
AMS having the detection unit physically separated from the gas stream by means of a sampling system
[EN 14181:2004, 3.9]
2.10
instability
change in the measured value comprised of drift and dispersion resulting from the change in the calibration
function over a stated period of unattended operation, for a given value of the air quality characteristic
NOTE 1 Drift and dispersion specify the monotonic and stochastic change with time of the output signal, respectively.
NOTE 2 This refers to a change in the response of the AMS to a determinant which does not change.
NOTE 3 Adapted from EN 14181:2004, 3.10.
2.11
instrument reading
indication of the measured value directly provided by the AMS without using the calibration function
[EN 14181:2004, 3.11]
2.12
intrinsic uncertainty
uncertainty component originating from the AMS itself, independent of the installation
2.13
legislation
Directives, Acts, ordinances and regulations
[EN 14181:2004, 3.12]
2.14
measurand
particular quantity subject to measurement
[EN 14181:2004, 3.13]
2.15
measured value
estimated value of the air quality characteristic derived from an output signal
NOTE 1 This usually involves calculations related to the calibration process and conversion to required quantities.
NOTE 2 Adapted from EN 14181:2004, 3.14.
2.16
non-extractive AMS
AMS having the detection unit in the gas stream or in a part of it
[EN 14181:2004, 3.15]
2.17
outlier
observation that lies an abnormal distance from other values in a set of data, and therefore has a low
probability of being a valid data point
2.18
period of unattended operation
maximum admissible interval of time for which the performance characteristics will remain within a predefined
range without external servicing, e.g. refill, calibration, adjustment
[EN 14181:2004, 3.16]
2.19
peripheral AMS or SRM
measuring system or SRM used to gather the data required to convert the measured values to standard
reference conditions, i.e. AMS or SRM for moisture, temperature, pressure and oxygen
[EN 14181:2004, 3.17]
2.20
precision
closeness of agreement of results obtained from the AMS for successive zero readings and successive span
readings at defined time intervals
[EN 14181:2004, 3.18]
2.21
reference material
material simulating a known concentration of the input parameter, by use of surrogates and traceable to
national standards
NOTE Surrogates normally used are calibration gasses, gas cells, gratings or filters.
[EN 14181:2004, 3.19]
2.22
response time
time interval between the instant of a sudden change in the value of the input quantity to an AMS and the time
as from which the value of the output quantity is reliably maintained above 90 % of the correct value of the
input quantity
[EN 15267-3:2008, 3.31]
2.23
span reading
instrument reading of the AMS for a simulation of the input parameter at a fixed elevated concentration
[EN 14181:2004, 3.21]
NOTE 1 This simulation is intended to test the measuring elements of the system, which contribute to its performance.
NOTE 2 The span reading is approximately 80 % of the measurement range.
2.24
standard conditions
conditions as given in the EU-directives to which measured values have to be standardised to verify
compliance with the emission limit values
[EN 14181:2004, 3.22]
2.25
standard deviation
positive square root of: the mean squared deviation from the arithmetic mean divided by the number of
degrees of freedom
NOTE The number of degrees of freedom is the number of measurements minus 1.
[EN 14181:2004, 3.23]
2.26
standard reference method
SRM
method described and standardised to define an air quality characteristic, temporarily installed on site for
verification purposes
NOTE Also known as a reference method.
[EN 14181:2004, 3.24]
2.27
uncertainty
parameter associated with the result of a measurement that characterises the dispersion of the values that
could reasonably be attributed to the measurand
[EN 14181:2004, 3.25]
2.28
variability
standard deviation of the differences of parallel measurements between the SRM and AMS
[EN 14181:2004, 3.26]
2.29
zero reading
instrument reading of the AMS on simulation of the input parameter at zero concentration, which tests the
measuring elements of the AMS, that contribute to its performance
NOTE Adapted from EN 14181:2004, 3.23.
3 Symbols and abbreviations
3.1 Symbols
a intercept of the calibration function
b slope of the calibration function
C mass concentration in milligrams per cubic metre (mg/m )
D
difference between measured SRM value y and calibrated AMS value yˆ
i
i i
average of D
D
i
E emission limit value
E extinction of the optical transmission monitor
otm
i
index
k
v test value for the variability test based on a χ -test, with a β-value of 50 %, for N numbers of
paired measurements
L
control limit value
L length of the measurement path in metres (m)
mp
m target value (chart centre line)
n number of checks
N number of paired samples in parallel measurements
P percentage value
R correlation coefficient
s standard deviation of the AMS at zero and span level
AMS
standard deviation of the differences D in parallel measurements
s i
D
t students t-factor for a confidence level of 95 %
0,95
th
x i measured signal obtained with the AMS
i
th
i measured result obtained with the SRM
y
i
yˆ best estimate for the true value, calculated from the AMS measured signal x by means of the
i i
calibration function
y span value
span
Z critical value in the Grubbs's test
th
Z test value of i data pair in the Grubbs's test
i
z weighted average taking the past and the last check into account
i
λ smoothing parameter
µ average diameter of the grains in the stack in micrometres (µm)
uncertainty derived from requirements of legislation
σ
3.2 Abbreviations
AMS automated measuring system
ARL average run length
AST annual surveillance test
ELV emission limit value
EWMA exponentially weighted moving average
LCL lower control limit
NO nitrogen oxides
x
QAL quality assurance level
SRM standard reference method
TOC total organic compounds
UCL upper control limit
4 General guidance on quality assurance and calibration
4.1 General
The role of this Technical Report is to provide guidance on the application of the European Standards
EN 14181:2004 on quality assurance of automated measuring systems used for monitoring stationary source
emissions and EN 13284-2:2004 on automated measuring systems used for the determination of low range
mass concentration of dust at stationary sources. Both European Standards are applicable to industrial plants
falling under the European Directives for the incineration of waste (2000/76/EC) and large combustion plants
(2001/80/EC), hence referred to as Directives in this Technical Report.
For simplicity, throughout this document, reference to EN 14181:2004 also refers to EN 13284-2:2004.
This Technical Report summarises the requirements of EN 14181:2004 and EN 13284-2:2004, and provides
guidance on how to perform each of the required tasks.
4.2 Regulatory framework and standards for monitoring
4.2.1 Monitoring requirements in the Directives
The Directives prescribe the use of European Standards for monitoring emissions and calibration of
automated measuring systems, or, if European Standards are not available, then the use of ISO, national or
other equivalent international standards that provide data of a suitable quality. The standards for monitoring
emissions are known as standard reference methods (SRM). Furthermore, the Directives specify overall
performance requirements for continuous monitoring through uncertainty allowances expressed as a 95 %
confidence interval. EN 14181:2004 presumes that the uncertainty of the AMS is expressed in the applicable
Directives as half of the length of a 95 % confidence interval as a percentage P of the emission limit value E.
4.2.2 Scope and structure of EN 14181:2004
EN 14181:2004 applies to AMS permanently installed at industrial plants regulated under the Directives. Also
EN 14181:2004 applies to the AMS themselves and not the data recording systems used with AMS. The
requirements for data acquisition and handling systems will be covered by a separate standard. The scope of
EN 14181:2004 applies to complete AMS as defined by EN 15267-3, which includes not just the analyser, but
also any sampling systems and other components required to analyse the stack gas and produce a
measurement.
Although EN 14181:2004 was developed for application at industrial plants covered by the Directives, it can
be applied to industrial plants covered by other EC laws, such as for other types of industrial plants regulated
under the Directive 96/61/EC for Integrated Pollution Prevention and Control (IPPC). EN 14181:2004 specifies
three quality assurance levels and an annual surveillance test. These are:
 QAL1 is a procedure to demonstrate that the AMS is suitable for the intended purpose before installation,
by meeting required performance standards EN ISO 14956, and the uncertainty allowances specified in
EU Directives. Since the publication of EN 14181:2004, CEN has published EN 15267-3 to apply
EN ISO 14956 for new AMS.
 QAL2 includes a set of functional tests to check that the AMS has been installed appropriately, and that
the AMS is operating correctly. The functional tests on the AMS are then followed by a procedure to
calibrate the AMS, using standard reference methods and then verify whether it still meets the required
uncertainty allowances, once installed. QAL2 establishes the traceability of the AMS measured values, to
the applicable standard. This provides a demonstration of compliance with legally binding emission limit
values.
 QAL3 is a procedure to maintain and demonstrate the required quality of the AMS during its normal
operation by checking the zero and span readings.
 AST is a set of functional tests to check the correct operation of the AMS, followed by a procedure to
evaluate the AMS to show that it continues to function correctly and the calibration function is still valid.
These quality assurance levels follow a logical sequence to demonstrate the suitability of the AMS, its correct
installation, commissioning, and calibration, followed by procedures to ensure a continuing and correct
operation (see Figure 1).
Figure 1 — Quality Assurance Levels from EN 14181
4.3 Roles and responsibilities
The operator of an industrial plant regulated by the Directives has the overall responsibility to comply with the
requirements of EN 14181:2004. The operator is responsible for organising the functional tests, according to
the requirements of the competent authority. The AMS manufacturer, AMS supplier, the operator's own
personnel, or a test laboratory may therefore perform the functional tests, depending on the requirements of
the competent authority.
Although the operator is responsible for compliance with the requirements of EN 14181:2004, this standard
specifies that the test laboratories which perform the parallel measurements, using standard reference
methods, as required by QAL2 and the AST, shall be either accredited to EN ISO/IEC 17025, or shall
otherwise meet the requirements of the competent authority. Therefore, EC member states may use national
systems for approving testing laboratories for QAL2 and the AST.
5 Application of QAL1
5.1 General
The purpose of QAL1 is to show that an AMS is potentially suitable for its intended task, by demonstrating that
the uncertainty at the emission limit value (ELV) will at least meet the uncertainty specified in the Directives.
The ability of the AMS to meet this uncertainty in turn depends on:
 the ability of the AMS to capture all or most of the measurement peaks over a sufficiently wide
measurement range, without compromising the required uncertainty at the ELV; and
 the ability of the AMS to be sufficiency stable once installed, i.e. any drift and precision are acceptable
within allowable specifications as defined by national or international standards.
5.2 AMS which are not yet installed at the plant
EN 14181:2004 refers to EN ISO 14956 when applying the requirements of QAL1. EN ISO 14956 describes a
procedure to determine the uncertainty, using performance criteria and test data for an AMS. However,
EN ISO 14956 only describes the mathematical procedure for determining the uncertainty. This standard does
not describe exactly which performance criteria and data to use within the calculations, nor how to perform the
tests to produce the data for the uncertainty calculations.
Therefore, CEN has published EN 15267-3, which specifies the performance criteria and test procedures for
automated measuring systems for monitoring emissions from stationary sources in the framework of
certification of automated measuring systems. This standard is both an application of EN ISO 14956, and a
means of demonstrating compliance with the QAL1 requirements of EN 14181:2004. This means that, if AMS
which have been tested to the requirements of EN 15267-3, and the results of these tests show that the
uncertainty meets the requirements of the Directives, then the AMS meets the requirements for QAL1.
EN 15267-3 and the national standards which preceded it make allowances for the uncertainty contributions of
the installation. For example, EN 15267-3 recommends that the uncertainty of the AMS, estimated using the
procedure in EN ISO 14956, is not be more than 75 % of the uncertainty allowance specified in the Directives.
This allows a margin of error for factors such as the uncertainty contributions from peripheral measurements
and stack gas inhomogeneity.
There are many AMS which have been tested and certified in accordance with national standards which
preceded EN 15267-3. In such cases, operators of industrial plants are advised to contact the competent
authorities for guidance.
Annex D of EN 15267-3:2007 provides an example of an uncertainty determination for an AMS, applying
EN ISO 14956 to determine the uncertainty.
5.3 AMS which are already installed at the plant
There can be cases where AMS are already installed at the plant, and where the AMS do not meet all of the
requirements of EN 15267-3. However, the performance criteria specified within EN 15267-3 are set at a level
which provides a margin of safety. This means that AMS which meet the requirements of EN 15267-3 are very
likely to meet the uncertainty allowances specified in the Directives. Therefore, an AMS which does not meet
the performance requirements of EN 15267-3 might still meet the uncertainty allowances specified within the
Directives. In such cases, the operator can minimise the effects of influence factors which increase the
uncertainty of the AMS once it is installed at the plant. For example, the AMS could be contained within a
climate-controlled chamber, which could minimise the influence of variations in ambient temperature on the
AMS.
Therefore if an AMS already installed at the plant does not meet the requirements of EN 15267-3, and hence
the requirements of QAL1, the competent authorities in EC member states may decide what action is
necessary. For example, the competent authority may state that if the AMS still meets the requirements of
QAL2, QAL3 and the AST, then the operator may keep the AMS for the rest of its design life.
6 Application of QAL2 and AST
6.1 Tasks within QAL2 and AST
QAL2 requires operators to assure that AMS are installed in the correct location, that there is sufficient access
to maintain, assess and control them, and to ensure that AMS are both calibrated and operating correctly. To
this end, EN 14181:2004 specifies two parts to QAL2, which are:
 A set of functional tests and checks to ensure that the AMS has been installed correctly and is functioning
at, or better than, the required performance levels; and that there are sufficient management-provisions in
place for the management and maintenance of the AMS. EN 15259 describes a procedure to identify the
best location for the sampling location of the AMS, in order to provide representative measurements.
 A set of repeated, parallel measurements using the SRM to verify whether the readings from the AMS are
reliable, and to derive the calibration function. This includes a set of statistical operations and tests
following the parallel measurements, to verify whether the AMS meets the uncertainty allowances
specified in the EU Directives.
Although the scope of EN 14181:2004 excludes systems for data acquisition, it is good practice to check the
data transfer from the AMS to the data acquisition and handling system during the QAL2 and AST.
6.2 Location and monitoring provisions for AMS
If an AMS is to give reliable results, then it is critical that the AMS is located in the correct position, such that it
measures a representative sample of the emissions. Furthermore, the sampling ports for periodic monitoring
also need to be located in a position which provides a representative sample, and allows a reliable
comparison of sampled emissions with the emissions measured by the AMS. Therefore EN 14181:2004
requires operators to ensure that the AMS are installed in the correct location, and that there is sufficient
access to assess, control and maintain them. EN 15259 provides guidance on the location of both AMS and
sampling ports, as well as appropriate provisions for monitoring.
6.3 Management system provisions for AMS
According to EN 14181:2004, the continued effective operation of AMS depends on the operator of the
industrial plant having both the provisions and procedures in place to manage and maintain the AMS.
Therefore, under A.4 of EN 14181:2004, there are requirements for documentation to support the
management of the AMS. Such procedures can include specific provisions for AMS, covering:
 selection;
 maintenance and servicing;
 responsibilities and training of personnel;
 calibration, quality assurance checks and controls;
 records and data management;
 prevention of unauthorised adjustment of the AMS and its data recording devices; and
 maintaining availability by spares, contingencies and back-up monitoring.
A systematic approach to managing and maintaining the AMS, documented through procedures within an
existing management system, meets the requirements of EN 14181:2004. Whilst operators can include these
management system provisions within existing management systems certified to standards such as
EN ISO 14001 and EN ISO 9001, more detailed guidance is available in a specific standard for measurement
management systems, EN ISO 10012.
6.4 Specific issues of the functional tests
6.4.1 General
EN 14181:2004 requires a set of functional tests to be carried out as part of the QAL2 and the AST. The
objective of the functional tests is to ensure that the AMS is working effectively, and that it is ready for parallel
tests using the SRM. Annex A of EN 14181:2004 contains a detailed description of the functional tests and
related activities. There are some issues to consider when performing the functional tests, such as
management system provisions for the AMS, zero and span checks, and the related linearity tests.
The test of lack-of-fit, response time and zero and span drift can be combined within one test. EN ISO 9169
describes a procedure to combine these tests. It is good practice to measure the response time for extractive
systems for the analyser alone, and then the analyser plus the sampling system. This allows the determination
of any losses in the sampling system, as well as the lag time within the sampling system.
6.4.2 Zero and span checks
EN 14181:2004 requires zero and span checks. EN 15267-3 and EN ISO 9169, for example, describe
procedures for these tests. Typically the zero and span checks require the use of reference materials. These
tests require the following:
 Each AMS for gaseous compounds has an injection point for the test gases as close as possible to the
sampling point in order to check the response time of the complete AMS. In addition to a check of the
complete system, injecting the test gas directly into the analyser of the AMS allows a check of the losses
in the sampling system, and the lag time caused by the sampling system.
 The output for the raw signal(s) is accessible and useable.
The lag times of the SRM and of the AMS, including the sampling systems, are needed to match the
measurements from the AMS to those from the SRM, taking into account any delays due to sampling systems
of the AMS and SRM. This applies to peripheral measurements, as well as the main measured components.
6.4.3 Linearity test
The linearity test (lack-of-fit) is specified for the AST but not for the QAL2 test. However, it can be beneficial to
perform this test during the QAL2 as well. For example, EN 14181:2004 permits the use of reference materials
to extrapolate the calibration function up to the ELV, subject to certain conditions. There are also a number of
issues to consider when planning and performing the linearity test.
It is good practice to use a test gas with an uncertainty which meets the requirements for test gases specified
in EN 15267-3. Additionally, using a gas-mixing system to provide different concentrations of the test gas has
a lower uncertainty than using different bottles of test gas for each required concentration.
In the case of HCl, HF and NH , for example, the test can take several hours and therefore compromise the
availability of the AMS. Therefore, both process operators and test laboratories can consider alternative
means of monitoring the process emissions whilst performing the test for linearity. Such alternative provisions
can include hot-standby AMS or portable standby AMS.
If the tests for linearity take several hours, then the test laboratory and operator may wish to consult the
competent authority about their position on maintenance operations, functional tests, and how these are seen
to affect AMS availability. In cases where the time taken for the linearity test is unacceptably long, EN 15267-3
describes a procedure to shorten tests when justified and can provide data of a suitable quality.
If the AMS measures sampled source emissions which are heated and without moisture removed, then it is
best practice to perform the test for linearity test using moist gases, using a combination of test gases and a
moisture generator.
If the AMS measures moisture, then it is good practice to perform the linearity test for moisture.
7 Calibration and validation of the AMS
7.1 Standard reference methods
The effective application of QAL2 and AST depends on the robust application of standard reference methods.
Accreditation to EN ISO/IEC 17025 for the applicable SRM is a means of achieving this aim. Therefore, many
competent authorities in EC Member states require test laboratories to be accredited to EN ISO/IEC 17025 for
the applicable SRM. However, EN ISO/IEC 17025 is a generic standard for the quality assurance of test
laboratories and can apply to any type of laboratory which performs services for both testing and calibration.
So CEN has produced a supplementary Technical Specification to EN ISO/IEC 17025, which is
CEN/TS 15675. This Technical Specification elaborates on the requirements of EN ISO/IEC 17025,
specifically for manual stack-emission monitoring. Therefore applying CEN/TS 15675 is likely to improve the
quality of the application of the SRM, and therefore improve the quality of the QAL2 and AST procedures.
7.2 Calibration using an SRM
7.2.1 General
Figure 2 illustrates the principle of linear calibration using an SRM in which the SRM data is compared with
the AMS data and is used to derive a calibration function. The AMS itself may have a bias in one direction or
another, depending on gain of the AMS and its offset relative to zero. A calibration function, in its simplest
form, can then be described by Equation (1):
y = a+ b x (1)
i i
where
th
x is the i measured signal obtained with the AMS, with i = 1 to N;
i
th
y is the i measured result obtained with the SRM, with i = 1 to N;
i
a is the intercept of the calibration function;
b is the slope of the calibration function.
There are two important factors to take into account when applying a calibration factor:
 The calibration function depends on linear responses to increasing concentrations of the measured
components, for both the SRM and AMS. However, it is probable that there will be some imprecision in
the agreement between the AMS and SRM measurements. This imprecision is caused by the
uncertainties of both the SRM and AMS measurements. Therefore it is important to minimise the
uncertainty of the SRM as far as practicable, as the uncertainty of the SRM could adversely affect both
the calibration function and the outcome of the variability test. Many SRM have been developed to have
an uncertainty which is typically half of the uncertainty required by the Directives. Applying
CEN/TS 15675 helps to assure the lowest possible uncertainty in the SRM.
 EN 14181:2004 specifies that there shall be evidence to show that the AMS produces readings at or near
zero, when the emissions are at or near zero.
Key
x AMS measured signal, in milliamperes (mA)
y SRM measured value, in milligrams per cubic metre (mg/m )
Figure 2 — Principle of linear calibration using a SRM
7.2.2 Spread of data
In order to meet the requirements of EN 14181:2004, QAL2 requires a set of data representing normal
operating conditions. Furthermore, the data needs to cover as wide a range as possible. Some industrial
processes can be varied in order to increase the emissions up to the ELV, in order to achieve a wide range of
concentrations in the sampled emissions. However, it is the decision of the competent authority whether to
allow adjustments to the industrial process, in order to artificially increase the emissions in order to provide a
wider spread of data. Ideally, the QAL2 takes place at a time when the emissions are likely to be their highest
and most varied; for example, when bag filters are replaced, emissions of particulate are temporarily higher
and this produces an ideal time to measure a wider range of emissions.
7.2.3 Number of data points
EN 14181:2004 specifies that the test laboratory needs to have at least 15 repetitions of the SRM for a QAL2,
and at least five repetitions for an AST. Therefore EN 14181:2004 recommends that the test laboratory takes
more than the minimum number of repetitions, because there is a significant chance that at least one result is
an outlier. Therefore, it is better to have more data than is necessary, whereas a test laboratory which has just
15 pairs of data for the SRM and AMS can find that there is an insufficient number of data points if even one
data point is an outlier. Therefore, it is better to take, for example, between 18 and 20 pairs of data, and then
determine if any of these data points are invalid using a procedure for analysing for the presence of outliers
(see 7.2.5 of this Technical Report).
At the same time, if a test laboratory takes well over the minimum number of paired samples for the AMS and
SRM, then all valid pairs of data need to be included in the QAL2 and AST calculations.
7.2.4 Values near zero
As EN 14181:2004 specifies that there shall be evidence to show that the AMS produce readings at or near
zero, when the emissions are at or near to zero, then measurements are needed at or near zero.
Ideally zero values are measured when the industrial plant is not producing emissions. If this is not possible,
then the competent authorities can allow the test laboratory to use surrogate values.
Figure 3 and Figure 4 illustrate the impact of clustered data points with and without measurements at zero. In
Figure 3, there are three values near zero and the calibration function shows an acceptable agreement
between the SRM and AMS values, with an approximate one to one mathematical relationship. However,
Figure 4 shows that in the absence of zero values within a similar set of data, there is a completely different
and incorrect calibration function. In such cases, EN 14181:2004 allows a forcing of the calibration line
through zero if the difference between the highest and lowest measured SRM concentrations at standard
conditions is smaller than 15 % of the ELV.

Key
x AMS measured signal, in milliamperes (mA)
y SRM measured value, in milligrams per cubic metre (mg/m )
Figure 3 — Example of an adequate spread of data for a set of QAL2 measurements

Key
x AMS measured signal, in milliamperes (mA)
y SRM measured value, in milligrams per cubic metre (mg/m )
Figure 4 — Example of a set of QAL2 measurements without measurements near zero
7.2.5 Invalid values and outliers
An outlier is defined as an invalid data point. Plotting AMS and SRM data on a graph shows whether there are
any obvious outliers. There can be several causes of invalid data, such as:
 errors in the SRM;
 failures of an AMS or instrument used for SRM; or
 automatic zero and span functions of the AMS.
Invalid data caused by these influences can be avoided by correct application of the SRM, the check of the
measuring systems and instruments before they are used in QAL2 and by switch-off of the automatic zero and
span checks during QAL2.
Data can appear to be outliers without there being an obvious and immediately apparent reason. However, as
EN 14181:2004 requires test laboratories to identify invalid data, this means that a test laboratory needs to
have a systematic approach to identifying outliers. There are several tests for outliers, although test
laboratories can choose any validated method. Most tests are based on the following principles:
ˆ
 In any data set of paired samples, (y , y ) with i = 1 to N, the differences D between the paired samples
i
i i
are distributed normally.
 There is an average of the differences of the paired samples, and there is a standard deviation s of the
D
differences.
 If the difference D between any pair of samples is greater or smaller than the average difference, by
i
more than two standard deviations s , then there is a strong chance that the paired sample is an outlier.
D
 After a test for outliers, the outlier which deviates the most from the average is rejected, and then the
outlier test is repeated.
Measurements above the ELV, however, can fail the outlier test because of signal-proportional uncertainty
contributions which can increase the uncertainty at larger values of the measured signal from the AMS. In
such situations, a visual inspection of the data can show whether such data points are true outliers.
Annex A shows an example of a procedure for determining outliers in a set of data.
7.2.6 Decision on Method A or Method B
EN 14181:2004 applies ISO 11095, which is a standard for calibrating measuring devices that have a linear
response to increasing values of the measurand. ISO 11095 in turn relies on the premise that a set of data is
linear and have a
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