ISO 14385-1:2014
(Main)Stationary source emissions — Greenhouse gases — Part 1: Calibration of automated measuring systems
Stationary source emissions — Greenhouse gases — Part 1: Calibration of automated measuring systems
ISO 14385-1:2014 specifies the procedures for establishing quality assurance for automated measuring systems (AMS) installed on industrial plants for the determination of the concentration of greenhouse gases in flue and waste gas and other flue gas parameters. ISO 14385-1:2014 specifies a procedure to calibrate the AMS and determine the variability of the measured values obtained by an AMS, which is suitable for the validation of an AMS following its installation. ISO 14385-1:2014 is designed to be used after the AMS has been accepted according to the procedures specified in ISO 14956.
Émissions de sources fixes — Gaz à effet de serre — Partie 1: Étalonnage des systèmes de mesurage automatiques
Emisije nepremičnih virov - Toplogredni plini - 1. del: Kalibracija avtomatskih merilnih sistemov
Ta dokument določa postopke za vzpostavitev ravni zagotavljanja kakovosti avtomatskih merilnih sistemov (AMS) v industrijskih obratih za določanje koncentracije toplogrednih plinov v dimovodih ter odpadnih plinov in drugih parametrov dimnega plina. Ta del standarda ISO 14385 določa postopek za kalibracijo avtomatskih merilnih sistemov in določitev spremenljivosti izmerjenih vrednosti, pridobljenih iz avtomatskih merilnih sistemov, ki je primeren za potrjevanje avtomatskega merilnega sistema po njegovi namestitvi. Ta del standarda ISO 14385 je zasnovan tako, da se uporablja po tem, ko je avtomatski merilni sistem potrjen in sprejet v skladu s postopki, določenimi v standardu ISO 14956.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-december-2019
Emisije nepremičnih virov - Toplogredni plini - 1. del: Kalibracija avtomatskih
merilnih sistemov
Stationary source emissions - Greenhouse gases - Part 1: Calibration of automated
measuring systems
Émissions de sources fixes - Gaz à effet de serre - Partie 1: Étalonnage des systèmes
de mesurage automatiques
Ta slovenski standard je istoveten z: ISO 14385-1:2014
ICS:
13.020.40 Onesnaževanje, nadzor nad Pollution, pollution control
onesnaževanjem in and conservation
ohranjanje
13.040.40 Emisije nepremičnih virov Stationary source emissions
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
INTERNATIONAL ISO
STANDARD 14385-1
First edition
2014-08-01
Stationary source emissions —
Greenhouse gases —
Part 1:
Calibration of automated measuring
systems
Émissions de sources fixes — Gaz à effet de serre —
Partie 1: Étalonnage des systèmes de mesurage automatiques
Reference number
©
ISO 2014
© ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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ii © ISO 2014 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations . 5
4.1 Symbols . 5
4.2 Abbreviations . 6
5 Principle . 6
5.1 General . 6
5.2 Limitations . 6
5.3 Measurement site and installation . 7
5.4 Testing laboratories performing SRM measurements . 8
6 Calibration and validation of the AMS . 8
6.1 General . 8
6.2 Functional test . 8
6.3 Calibration and validation of multiple/complex measurement systems . 8
6.4 Parallel measurements with an SRM . 9
6.5 Procedure: calibration and validation of the AMS by means of parallel measurements .11
6.6 Report .18
7 Documentation .18
Annex A (normative) Functional test of AMS .19
Annex B (normative) Test of linearity .23
Annex C (normative) Documentation .25
Annex D (informative) Example of calculation of the calibration function .27
Annex E (informative) Procedure for the identification of outliers .30
Annex F (informative) Measurement uncertainty .34
Bibliography .35
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 146, Air quality, Subcommittee SC 1, Stationary
source emissions.
ISO 14385 consists of the following parts, under the general title Stationary source emissions —
Greenhouse gases:
— Part 1: Calibration of automated measuring systems
— Part 2: Ongoing quality control of automated measuring systems
iv © ISO 2014 – All rights reserved
Introduction
The measurement of greenhouse gas emissions (carbon dioxide, nitrous oxide, methane) in a framework
of emission trading requires an equal and known quality of data.
This part of ISO 14385 describes the quality assurance procedures for calibration and ongoing quality
control needed to ensure that automated measuring systems (AMS) installed to measure emissions
of greenhouse gases to air are capable of meeting the uncertainty requirements on measured values
specified, e.g. by legislation, competent authorities, or in an emission trade scheme.
INTERNATIONAL STANDARD ISO 14385-1:2014(E)
Stationary source emissions — Greenhouse gases —
Part 1:
Calibration of automated measuring systems
1 Scope
This part of ISO 14385 specifies the procedures for establishing quality assurance for automated
measuring systems (AMS) installed on industrial plants for the determination of the concentration of
greenhouse gases in flue and waste gas and other flue gas parameters.
This part of ISO 14385 specifies a procedure to calibrate the AMS and determine the variability of
the measured values obtained by an AMS, which is suitable for the validation of an AMS following its
installation.
This part of ISO 14385 is designed to be used after the AMS has been accepted according to the procedures
specified in ISO 14956.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 14385-2, Stationary source emissions — Greenhouse gases — Part 2: Ongoing quality control of
automated measuring systems
ISO 14956, Air quality — Evaluation of the suitability of a measurement procedure by comparison with a
required measurement uncertainty
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
automated measuring system
AMS
measuring system permanently installed on site for continuous monitoring of emissions
Note 1 to entry: An AMS is a method which is traceable to a reference method.
Note 2 to entry: Apart from the analyser, an AMS includes facilities for taking samples (e.g. sample probe, sample
gas lines, filters, flow meters, regulators, delivery pumps, blowers) and for sample conditioning (e.g. dust filter,
water vapour removal devices, converters, diluters). This definition also includes testing and adjusting devices
that are required for regular functional checks.
3.2
calibration function
linear relationship between the values of the SRM and the AMS with the assumption of a constant
residual standard deviation
3.3
calibration gas
gas of known composition that can be used to check the response of the AMS
3.4
competent authority
organization or organizations which implement the requirements of legislation and regulate installations
which must comply with the requirements of legislation
3.5
confidence interval
interval estimator (T , T ) for the parameter θ with the statistics T and T as interval limits and for
1 2 1 2
which it holds that P[T < θ < T ] ≥ 1 – α
1 2
Note 1 to entry: The two-sided 95 % confidence interval of a normal distribution is illustrated in Figure 1, where
T = Θ – 1,96σ is the lower 95 % confidence limit;
1 0
T = Θ + 1,96σ is the upper 95 % confidence limit;
2 0
I = T – T = 2 × 1,96 × σ is the length of the 95 % confidence interval;
2 1 0
σ = I / (2 × 1,96) is the standard deviation associated with a 95 % confidence interval;
n is the number of observed values;
f is the frequency;
m is the measured value.
Figure 1 — Illustration of the 95 % confidence interval of a normal distribution
Note 2 to entry: In this part of ISO 14385, the standard deviation, σ is estimated by parallel measurements
0,
with an SRM. It is assumed that the requirement for σ , presented in terms of an allowable uncertainty budget,
i.e. variability is provided by the regulators. In the procedures of this part of ISO 14385, the premise is that the
required variability is given as σ itself, or as a quarter of the length of the full 95 % confidence interval.
[SOURCE: ISO 3534-1:2006, 1.28, modified: Figure 1 has been added. Notes 1 and 2 are different.]
3.6
drift
monotonic change of the calibration function over stated maintenance interval, which results in a change
of the measured value
3.7
extractive AMS
AMS having the detection unit physically separated from the gas stream by means of a sampling system
2 © ISO 2014 – All rights reserved
3.8
in-situ AMS
AMS having the detection unit in the gas stream, or in a part of it
3.9
instrument reading
indication of the measured value directly provided by the AMS without using the calibration function
3.10
legislation
directives, acts, ordinances, and regulations
3.11
low-level cluster
cluster of measurement values less than the maximum permissible uncertainty and between 0 % and
15 % of the lowest measuring range
3.12
measurand
[5]
particular quantity subject to measurement
3.13
measured component
constituent of the waste gas for which a defined measurand is to be determined by measurement
3.14
measured value
estimated value of the measurand derived from an output signal
Note 1 to entry: This usually involves calculations related to the calibration process and conversion to required
quantities
Note 2 to entry: A measured value is a short-term average. The averaging time can be, e.g. 10 min, 30 min, or 1 h.
3.15
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
Note 1 to entry: This is also known as the maintenance interval.
3.16
peripheral parameter
specified physical or chemical quantity which is needed for conversion of the AMS measured value to
standard conditions
3.17
peripheral AMS
AMS used to gather the data required to convert the AMS measured value to standard conditions
Note 1 to entry: A peripheral AMS is used to measure water vapour, temperature, pressure, and oxygen.
3.18
peripheral SRM
SRM used to gather the data required to convert the SRM measured values to AMS or standard conditions
Note 1 to entry: A peripheral SRM is used to measure water vapour, temperature, pressure, and oxygen.
3.19
precision
closeness of agreement of results obtained from the AMS for successive zero readings and successive
span readings at defined time intervals
3.20
reference material
substance or mixture of substances with a known concentration within specified limits, or a device of
known characteristics
Note 1 to entry: Normally used are calibration gases, gas cells, gratings, or filters.
3.21
response time
t90
time interval between the instance 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
Note 1 to entry: The response time is also referred to as the 90 % time.
3.22
span reading
instrument reading of the AMS for a simulation of the input parameter at a fixed elevated concentration.
This simulation should test as much as possible all the measuring elements of the system, which
contribute significantly to its performance.
Note 1 to entry: The span reading is approximately 80 % of the measured range.
3.23
standard conditions
conditions as given in legislation to which measured values have to be standardized
3.24
standard deviation
positive square root of the mean squared deviation from the arithmetic mean, divided by the degrees
of freedom
Note 1 to entry: The number of degrees of freedom is the number of measurements minus 1.
3.25
Standard Reference Method
SRM
method described and standardised to define a measurand, temporarily conducted on site for verification
purposes
Note 1 to entry: Also known as a reference method.
3.26
uncertainty
parameter associated with the result of a measurement that characterises the dispersion of the values
[5]
that could reasonably be attributed to the measurand
3.27
variability
standard deviation of the differences of parallel measurements between the SRM and AMS
3.28
zero reading
instrument reading of the AMS on simulation of the input parameter at zero concentration, which shall
test as much as possible all the measuring elements of the AMS, that contribute significantly to its
performance
4 © ISO 2014 – All rights reserved
4 Symbols and abbreviations
4.1 Symbols
a intercept of the calibration function
â best estimate of a
b slope of the calibration function
ˆ best estimate of b
b
D difference between SRM value y and calibrated AMS measured value ŷ
i i i
average of D
i
D
E maximum value of measuring range
k test value for variability (based on a χ -test, with a β-value of 50 %, for N numbers of paired measure-
v
ments)
N number of paired samples in parallel measurements
σ standard deviation of the differences D in parallel measurements
i
t value of the t distribution for a significance level of 95 % and a number of degrees of freedom of N – 1
0,95; N–1
u uncertainty due to instability (expressed as a standard deviation)
inst
u uncertainty due to influence of temperature (expressed as a standard deviation)
temp
u uncertainty due to influence of pressure (expressed as a standard deviation)
pres
u uncertainty due to influence of voltage (expressed as a standard deviation)
volt
u any other uncertainty that can influence the zero and span reading (expressed as a standard devia-
others
tion)
th
x i measured signal obtained with the AMS at AMS measuring conditions
i
x average of AMS measured signals x
i
th
y i measured value obtained with the SRM
i
y
average of the SRM measured values y
i
y SRM measured value y at standard conditions
i,s i
y lowest SRM measured value at standard conditions
s,min
y highest SRM measured value at standard conditions
s,max
ŷ best estimate for the “true value”, calculated from the AMS measured signal x by means of the cali-
i i
bration function
ŷ best estimate for the “true value”, calculated from the AMS measured signal x at standard conditions
i,s i
ŷ best estimate for the “true value”, calculated from the maximum value of the AMS measured signals x
s,max i
at standard conditions
Z offset (the difference between the AMS zero reading and the zero)
s standard deviation of the AMS used in ongoing quality control
AMS
α significance level
ԑ deviation between y and the expected value σ standard deviation associated with the uncertainty
i i 0
derived from requirements of legislation
4.2 Abbreviations
AMS automated measuring system
AST annual surveillance test
QA quality assurance
SRM Standard Reference Method
5 Principle
5.1 General
An AMS to be used shall be proven suitable for its measuring task (parameter and composition of the flue
gas) by use of the procedures specified in ISO 14956. Using this part of ISO 14385, it shall be proven that
the total uncertainty of the results obtained from the AMS meets the specification for uncertainty stated
in legislation or in requirements and specifications established in an international trading program. In
ISO 14956, the total uncertainty required by the relevant regulations is calculated by summing all the
relevant uncertainty components arising from the individual performance.
This part of ISO 14385 provides a procedure for the validation and calibration of an AMS. It consists
of the determination of the calibration function and its variability, and a test of the variability of the
measured values of the AMS compared with the uncertainty given by legislation or in requirements and
specifications established in international trading programs. The tests are based on a number of parallel
measurements performed with a Standard Reference Method (SRM). The variability of the measured
values obtained with the AMS can then be evaluated against the maximum permissible uncertainty.
The tests are performed on AMS that have been correctly installed and commissioned.
The tests can be used to
a) establish a calibration function over a range of plant operating conditions and
b) calibrate the AMS and demonstrate that an AMS meets the required accuracy at a constant operating
load.
The procedure is repeated periodically after a major change of plant operation, after a failure of the
AMS, or as required by legislation.
5.2 Limitations
Figure 2 illustrates the components of the AMS covered by this part of ISO 14385.
6 © ISO 2014 – All rights reserved
Figure 2 — Limits for the QA of the AMS excluding the data acquisition and handling system
NOTE 1 The influence of the uncertainty of the measurement results, which arise from the data acquisition
recording and handling system of the AMS or of the plant system and its determination, are excluded from this
part of ISO 14385.
NOTE 2 The performance of the data collection and recording system can be as influential as the AMS
performance in determining the quality of the results obtained from the whole measuring system/process. There
are different requirements for data collection recording and presentation in different countries.
When conducting parallel measurements, the measured signals from the AMS are taken directly from
the AMS (e.g. expressed as analogue or digital signal) during the calibration and annual surveillance test
(AST) procedures specified in this part of ISO 14385 by using an independent data collection system
provided by the organization(s) carrying out the calibration and AST tests, as specified in ISO 14385-2.
All data shall be recorded in their uncorrected form (without corrections for, e.g. temperature and
oxygen). A plant data collection system with quality control can additionally be used to collect the
measured signal from the AMS.
5.3 Measurement site and installation
The AMS shall be installed in accordance with the requirements of the relevant national or international
standards, as specified by legislation, competent authorities, or in emission trade scheme. Special
attention shall be given to ensure that the AMS is readily accessible for regular maintenance and other
necessary activities.
NOTE The AMS is intended to be positioned as far as practical so that it measures a sample representative of
the stack gas composition.
All measurements shall be carried out on a suitable AMS and peripheral AMS installed within an
appropriate working environment.
The working platform used to access the AMS shall readily allow parallel measurements to be performed
using an SRM. The sampling ports for measurements with the SRM shall be placed as close as possible,
but not more than three times the equivalent diameter up- or down-stream of the location of the AMS,
in order to achieve comparable measurements between AMS and SRM.
It is necessary to have good access to the AMS to enable inspections to take place and also to minimize
time taken to implement the quality assurance procedures of this part of ISO 14385. A clean, well-
ventilated, and well-lit working space around the AMS is required to enable the staff to perform this
work effectively. Suitable protection is required for the personnel and the equipment, if the working
platform is exposed to the weather.
5.4 Testing laboratories performing SRM measurements
The testing laboratories, which perform the measurements with the SRM, shall be accredited for this
task according to ISO/IEC 17025 or shall be approved directly by the relevant competent authority.
6 Calibration and validation of the AMS
6.1 General
Testing shall cover the following items:
— installation of the AMS;
— functional test of the AMS;
— calibration of the AMS by means of parallel measurements with an SRM and, if necessary, in
combination with calibration gases;
— validation of the AMS (determination of the variability of the AMS and the check of compliance with
the maximum permissible uncertainty or determination of the relative uncertainty).
A calibration procedure shall be performed for all measurands at least every 5 years for every AMS
and more frequently if so required by legislation, requirements, and specifications established in an
international trading program or the competent authority.
Furthermore, a calibration procedure shall be performed for all the measurands influenced by
— any major change in plant operation (e.g. change in flue gas abatement system or change of fuel) or
— any major changes or repairs to the AMS, which will influence the results obtained significantly.
The results of the calibration procedure shall be reported within 6 months after the changes. During the
period before a new calibration function has been established, the previous calibration function (where
necessary with extrapolation) shall be used.
The measurement range shall be chosen to ensure the expected measurement values are between 25 %
and 75 % of the maximum of this range.
6.2 Functional test
The requirements for installation and the measurement site as specified in 5.3 shall be checked.
If peripheral AMS is used to convert the measured values to other conditions, these AMS shall be subject
of functional tests.
NOTE Since the AMS and SRM measured values are converted to other conditions by independently
determined data sets of the peripheral parameters, the uncertainties in the peripheral parameters are attributed
to the AMS of the air pollutant in the variability test.
The functional test before calibration shall be performed according to Annex A. The period between the
functional test and the calibration shall be limited to 1 month.
The specific precautions to be taken should depend on the individual location.
6.3 Calibration and validation of multiple/complex measurement systems
Although the procedures in this part of ISO 14385 are primarily describing the calibration and
validation of single instruments, the same procedures can be used for the calibration and validation
of multiple/complex measurement systems. For instance, in many countries, emission limit values are
expressed in concentrations at standard conditions (dry flue gas with temperature 273,15 K, pressure
8 © ISO 2014 – All rights reserved
1013 hPa, and a specified oxygen concentration). In such a case, the measurement system consists of
several analysers and measuring devices (peripheral AMS) (analyser for air-polluting compound, oxygen
analyser, measuring devices for temperature, pressure, and water vapour).
If legislation or requirements and specifications established in an international trading program are
requiring calibration and validation of concentrations of air-polluting compounds at standard conditions,
two options are possible.
First, this can be realized by calibration of the results of the individual analysers and measuring devices
using the measurement results of the appropriate reference methods for each of the components in the
calculation (air-polluting compound, oxygen, temperature, pressure, and water vapour). The calibrated
results are then used for conversion by calculation to concentrations at standard conditions.
Alternatively, the results of the individual analysers and measuring devices are converted to standard
conditions and then calibrated to the converted results of the reference methods.
The standard deviation used in the validation procedure has to be calculated by using Formula (11) and
on the basis of the normalized calibrated AMS values and the normalized SRM values.
6.4 Parallel measurements with an SRM
Parallel measurements shall be performed with the AMS and SRM in order to calibrate and/or validate
the AMS by use of an independent method.
It is not sufficient to use reference materials alone to obtain the calibration functions and this is therefore
not permitted. This is because these reference materials do not replicate sufficiently the matrix stack
gas, they cannot be used to establish that the sampling point(s) of the AMS are representative, and
they are not used with the sampling system in all cases. However, if there are limited variations in the
results obtained in the AMS/SRM tests, and the measured concentrations are more than 20 % below
the maximum value of the normal measuring range, an extrapolation of the calibration function to the
highest annual value can be verified by the use of appropriate reference materials, taking into account
the effects of interfering substances on the AMS, where appropriate.
If clear and distinct operating modes of the plant process are part of its normal operation (for example,
changes of fuel), additional calibrations shall be performed and a calibration function established for
each operational mode if the operation affects the calibration curve.
NOTE 1 It is recommended that a preliminary test be carried out in order to evaluate if a full calibration over
the whole concentration range can be performed. Otherwise, a competent authority is intended to judge if, based
on its experience, it is reasonable to establish one calibration function that covers all normal changes in the
process.
In order to ensure that the calibration function is valid for the range of conditions within which the plant
will operate, the concentrations during the calibration shall be varied as much as possible within the
normal operations of the plant. This shall ensure that the calibration of the AMS is valid over as large a
range as possible, and also that it covers most operational situations.
The test for variability shall be performed (see 6.5.6) for each calibration function, i.e. for each operating
mode of the plant.
An SRM shall be used to measure the emissions through representative sampling in the duct, which is
as close as possible to the AMS. The sampling of the AMS and SRM shall not influence the results of both
measurement systems.
The presence of the equipment specified in the SRM shall not influence or disturb the AMS measurements.
For each calibration, a minimum of 15 valid parallel measurements shall be made with the plant
operating normally. These measurements shall be uniformly spread both over at least 3 d and over each
of the measuring days of normally 8 h to 10 h (e.g. not five measurements in the morning and none in the
afternoon) and be performed within a period of 4 weeks.
NOTE 2 The required spread of a minimum of 15 valid measurements over 3 d is essential in minimising the
effect of influences of the subsequent measurement results (i.e. to avoid auto-correlation between the calculated
differences in the results of the AMS and SRM). The alternative of performing more measurements within a
shorter time interval can lead to the establishment of an invalid calibration function.
NOTE 3 A minimum of 15 valid measurements can, in practice, require that more than 15 samples be taken,
since some samples can be deemed to be invalid during subsequent analysis because of inadequate quality.
NOTE 4 The requirement that the measurements need to be uniformly spread over at least 3 d does not imply
that the measurements need to be performed within three consecutive days.
If the calibration is not the first calibration being carried out on the AMS and the operator can prove
that at least 95 % of the AMS measured values obtained since the last calibration or annual surveillance
test (see ISO 14385-2) are less than the maximum permissible expanded uncertainty, the number of
measurements can be reduced to five parallel measurements performed on 1 d. The results of these five
measurements shall be used to check the validity of the existing calibration function. If the calibration
function appears not to be valid, the number of parallel measurements shall be increased to 15 parallel
measurements to calculate a new calibration function.
Examples of expanded uncertainty are given in Annex F.
A set of measurements is valid when all of the requirements below are fulfilled:
— the SRM measurements are performed according to the accepted standard;
— the time period of each AMS measured signal shall cover at least 90 % of the averaging time
[excluding all of the measured signals which are above 100 % or below 0 % of the measuring range
of the AMS, signals obtained during internal checks (auto calibration), and signals obtained during
any other malfunctioning of the AMS].
During the parallel measurements with the AMS and SRM, each result is considered as a measurement
pair (one AMS measured signal and one SRM measured value) and these shall cover the same time period.
The sampling time for each of the parallel measurements shall be at least 30 min, or at least four times
the response time of the AMS, including the sampling system (as determined during the response time
measurements carried out during the procedures according to ISO 14956), whichever is the greater. In
general, the sampling time should equal the shortest averaging time, which is required by the legislation
or as defined in an international trading program. The recording system shall have an averaging time
significantly shorter than the response time of the AMS.
If the sampling time is shorter than 1 h, then the time interval between the start of each sample shall be
longer than 1 h.
The results obtained from the SRM shall be expressed under the same conditions as measured by the
AMS (e.g. conditions of pressure, temperature, etc.). In order to establish the calibration function and
perform the variability test, all additional parameters and values included in the corrections to AMS
conditions and standard conditions shall be obtained for each measurement pair.
EXAMPLE If the AMS measures N O in units of mg/m in stack gas containing water vapour, then the SRM
results are expressed in the same units (e.g. mg/m in the stack gas with the same water vapour concentration).
The 15 parallel measurements can be performed in less than 3 d if
— at least 97 % of the validated half-hourly values obtained in the period since the last calibration
were smaller than 30 % of the measurement range value specified for half-hourly values or
— at least 99 % of the validated half-hourly values obtained in the period since the last calibration do
not deviate from the average of all validated half-hourly values by more than 5 %.
In these cases, the interval between the start of each sampling can be less than 1 h.
10 © ISO 2014 – All rights reserved
In order to fulfil the requirement that the calibration of the AMS is valid over as large a range as possible,
and that it covers most operational situations, parallel measurements over 3 d are generally required.
However, this can require several manual SRM measurements of the water vapour concentration. If
calibrated AMS measured values for water vapour are available, these can be used to convert the SRM
data to dry or wet basis. When wet abatement techniques are used, the water vapour concentration is
often nearly constant and extended measurement of the water vapour concentration is of little purpose.
In those situations, conversion of SRM data to dry or wet basis as required can be carried out using
calculated AMS water vapour measurements.
6.5 Procedure: calibration and validation of the AMS by means of parallel measure-
ments
6.5.1 General
In this procedure, the calibration function of the AMS and its variability are determined by means of
parallel measurements with an SRM. The variability of the measured values obtained with the AMS is
then evaluated against the maximum permissible uncertainty.
The sequence of the tests to be carried out is shown in Figure 3.
See 6.4
See 6.5.2
See 6.5.3
See 6.5.5
See 6.5.6
See 6.6
Figure 3 — Flow diagram for the calibration and variability tests
Examples of calculation of the calibration function and of the variability test are given in Annex D.
NOTE If change in fuel mixture is a part of the normal operation mode of the plant, it is recommended that
the fuel mixture is varied during the parallel measurements.
6.5.2 Data evaluation
6.5.2.1 Preparation of data
The steps for providing data required for establishing the calibration function and performing the test
of variability are illustrated in Figure 4.
6.5.2.2
NOTE The figure in the circles indicates the sequence of the steps.
Figure 4 — Flow chart describing the steps in calibration procedure and test for variability
The AMS shall be calibrated at the condition of the exhaust gas as measured by the AMS. Therefore, the
SRM values shall be converted to AMS measuring conditions, if necessary, giving SRM measured values,
y , to be expressed in concentration units (e.g. mg/m ).
m
The measured signals from the AMS, x can be either a signal in an electrical unit (e.g. mA or Volt) or in a
i
concentration unit (e.g. mg/m ).
NOTE For a non-extractive AMS that measures the gas directly, the calibration function reported shall be
at the operating conditions. For an extractive AMS measuring at specified conditions, the calibration function is
reported at these specified conditions.
The data sets obtained in the parallel measurements shall be checked for possible outliers (see Annex E).
The method used to assess outliers and reasons for excluding outliers shall be given in the calibration
report. Outliers shall be reported and identified in the calibration diagrams. This part of ISO 14385
requires at least 15 valid data points for a calibration function. If points are excluded, e.g. through the
use of outlier tests, this requirement can be failed. It is therefore recommended that additional data
points be taken, to allow for the exclusion of outliers. If this is not done, the calibration can be invalid.
12 © ISO 2014 – All rights reserved
6.5.2.2 Establishing the calibration function
It is presupposed in this part of ISO 14385 that the calibration function is linear and has a constant
residual standard deviation. The calibration function shall be described by Formula (1) [ISO 11095]:
ya=+bx +ε (1)
ii i
where
th
x is the i result of the AMS; i = 1 to N; N ≥ 15;
i
th
y is the i result of the SRM; i = 1 to N; N ≥ 15;
i
ε is the deviation between y and the expected value;
i i
a is the intercept of the calibration function;
b is the slope of the calibration function.
The general procedure [Formula (4) and (5)] requires a sufficient range of the measured concentrations
to give a valid calibration of the AMS for the complete range of concentrations encountered during normal
operation. As stated in 6.5, it is essential that the concentration range is as large as possible within the
normal operation of the plant for a valid calibration function. However, at a large number of plants, it
can be difficult under normal operating conditions to achieve a sufficiently large concentration range.
In such cases, in which the concentration range (measured with the SRM) is less than the maximum
permissible uncertainty, another (similar) procedure is given below (procedure b).
NOTE 1 If the concentration range is slightly bigger than maximum permissible uncertainty, and if Formulae (4)
and (5) result in an inadequate calibration function (e.g. a function with negative slope), Formulae (6) and (7) can
be used instead.
Formulae (2) and (3) shall be calculated:
N
x= x (2)
∑ i
N
i=1
N
y= y (3)
∑ i
N
i=1
The difference ( y – y ) between the highest and lowest measured SRM concentration at standard
s,max s,min
conditions shall be calculated.
a) If (y – y ) is greater than or equal to the maximum permissible uncertainty, calculate:
s,max s,min
N
()xx−−yy
()
∑
ii
i=1
ˆ
b = (4)
N
()xx−
∑
i
i=1
ˆ
ây= - bx (5)
b) If (y – y ) is smaller than the maximum permissible uncertainty, calculate:
s,max s,min
y
ˆ
b = (6)
xZ−
ˆ
âb=− ×Z (7)
where the offset (Z) is the difference between the AMS zero reading and the zero.
NOTE 2 For several AMS, the offset is 4 mA.
For calculation b), it is essential that, prior to the parallel measurements, it is proven that the AMS gives
a reading at, or below, detection limit (as demonstrated in the procedures according to ISO 14956) at
a zero concentration. Before calibration is performed, it shall be proven that the AMS is commissioned
satisfactorily, e.g. as specified by the AMS supplier and/or manufacturer. It shall also be shown and
documented that the AMS gives a zero reading on a zero concentration (as stated in 6.2).
If the spread of the data is less than the maximum permissible uncertainty, a calibration function
calculated as a linear regression function forced through the lower reference point (which is the zero
point if the AMS reads zero) can be used, provided the functional test has proven that it is linear down
to the lower reference point or zero.
The results shall be plotted on an x-y graph in order to show explicitly the calibration function and the
valid calibration range.
6.5.2.3 Low-level clusters
There are typically three types of patterns of emissions from industrial plants; in addition to the patterns
of data described in 6.5.2.2 and assessed using procedure a or procedu
...
INTERNATIONAL ISO
STANDARD 14385-1
First edition
2014-08-01
Stationary source emissions —
Greenhouse gases —
Part 1:
Calibration of automated measuring
systems
Émissions de sources fixes — Gaz à effet de serre —
Partie 1: Étalonnage des systèmes de mesurage automatiques
Reference number
©
ISO 2014
© ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations . 5
4.1 Symbols . 5
4.2 Abbreviations . 6
5 Principle . 6
5.1 General . 6
5.2 Limitations . 6
5.3 Measurement site and installation . 7
5.4 Testing laboratories performing SRM measurements . 8
6 Calibration and validation of the AMS . 8
6.1 General . 8
6.2 Functional test . 8
6.3 Calibration and validation of multiple/complex measurement systems . 8
6.4 Parallel measurements with an SRM . 9
6.5 Procedure: calibration and validation of the AMS by means of parallel measurements .11
6.6 Report .18
7 Documentation .18
Annex A (normative) Functional test of AMS .19
Annex B (normative) Test of linearity .23
Annex C (normative) Documentation .25
Annex D (informative) Example of calculation of the calibration function .27
Annex E (informative) Procedure for the identification of outliers .30
Annex F (informative) Measurement uncertainty .34
Bibliography .35
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 146, Air quality, Subcommittee SC 1, Stationary
source emissions.
ISO 14385 consists of the following parts, under the general title Stationary source emissions —
Greenhouse gases:
— Part 1: Calibration of automated measuring systems
— Part 2: Ongoing quality control of automated measuring systems
iv © ISO 2014 – All rights reserved
Introduction
The measurement of greenhouse gas emissions (carbon dioxide, nitrous oxide, methane) in a framework
of emission trading requires an equal and known quality of data.
This part of ISO 14385 describes the quality assurance procedures for calibration and ongoing quality
control needed to ensure that automated measuring systems (AMS) installed to measure emissions
of greenhouse gases to air are capable of meeting the uncertainty requirements on measured values
specified, e.g. by legislation, competent authorities, or in an emission trade scheme.
INTERNATIONAL STANDARD ISO 14385-1:2014(E)
Stationary source emissions — Greenhouse gases —
Part 1:
Calibration of automated measuring systems
1 Scope
This part of ISO 14385 specifies the procedures for establishing quality assurance for automated
measuring systems (AMS) installed on industrial plants for the determination of the concentration of
greenhouse gases in flue and waste gas and other flue gas parameters.
This part of ISO 14385 specifies a procedure to calibrate the AMS and determine the variability of
the measured values obtained by an AMS, which is suitable for the validation of an AMS following its
installation.
This part of ISO 14385 is designed to be used after the AMS has been accepted according to the procedures
specified in ISO 14956.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 14385-2, Stationary source emissions — Greenhouse gases — Part 2: Ongoing quality control of
automated measuring systems
ISO 14956, Air quality — Evaluation of the suitability of a measurement procedure by comparison with a
required measurement uncertainty
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
automated measuring system
AMS
measuring system permanently installed on site for continuous monitoring of emissions
Note 1 to entry: An AMS is a method which is traceable to a reference method.
Note 2 to entry: Apart from the analyser, an AMS includes facilities for taking samples (e.g. sample probe, sample
gas lines, filters, flow meters, regulators, delivery pumps, blowers) and for sample conditioning (e.g. dust filter,
water vapour removal devices, converters, diluters). This definition also includes testing and adjusting devices
that are required for regular functional checks.
3.2
calibration function
linear relationship between the values of the SRM and the AMS with the assumption of a constant
residual standard deviation
3.3
calibration gas
gas of known composition that can be used to check the response of the AMS
3.4
competent authority
organization or organizations which implement the requirements of legislation and regulate installations
which must comply with the requirements of legislation
3.5
confidence interval
interval estimator (T , T ) for the parameter θ with the statistics T and T as interval limits and for
1 2 1 2
which it holds that P[T < θ < T ] ≥ 1 – α
1 2
Note 1 to entry: The two-sided 95 % confidence interval of a normal distribution is illustrated in Figure 1, where
T = Θ – 1,96σ is the lower 95 % confidence limit;
1 0
T = Θ + 1,96σ is the upper 95 % confidence limit;
2 0
I = T – T = 2 × 1,96 × σ is the length of the 95 % confidence interval;
2 1 0
σ = I / (2 × 1,96) is the standard deviation associated with a 95 % confidence interval;
n is the number of observed values;
f is the frequency;
m is the measured value.
Figure 1 — Illustration of the 95 % confidence interval of a normal distribution
Note 2 to entry: In this part of ISO 14385, the standard deviation, σ is estimated by parallel measurements
0,
with an SRM. It is assumed that the requirement for σ , presented in terms of an allowable uncertainty budget,
i.e. variability is provided by the regulators. In the procedures of this part of ISO 14385, the premise is that the
required variability is given as σ itself, or as a quarter of the length of the full 95 % confidence interval.
[SOURCE: ISO 3534-1:2006, 1.28, modified: Figure 1 has been added. Notes 1 and 2 are different.]
3.6
drift
monotonic change of the calibration function over stated maintenance interval, which results in a change
of the measured value
3.7
extractive AMS
AMS having the detection unit physically separated from the gas stream by means of a sampling system
2 © ISO 2014 – All rights reserved
3.8
in-situ AMS
AMS having the detection unit in the gas stream, or in a part of it
3.9
instrument reading
indication of the measured value directly provided by the AMS without using the calibration function
3.10
legislation
directives, acts, ordinances, and regulations
3.11
low-level cluster
cluster of measurement values less than the maximum permissible uncertainty and between 0 % and
15 % of the lowest measuring range
3.12
measurand
[5]
particular quantity subject to measurement
3.13
measured component
constituent of the waste gas for which a defined measurand is to be determined by measurement
3.14
measured value
estimated value of the measurand derived from an output signal
Note 1 to entry: This usually involves calculations related to the calibration process and conversion to required
quantities
Note 2 to entry: A measured value is a short-term average. The averaging time can be, e.g. 10 min, 30 min, or 1 h.
3.15
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
Note 1 to entry: This is also known as the maintenance interval.
3.16
peripheral parameter
specified physical or chemical quantity which is needed for conversion of the AMS measured value to
standard conditions
3.17
peripheral AMS
AMS used to gather the data required to convert the AMS measured value to standard conditions
Note 1 to entry: A peripheral AMS is used to measure water vapour, temperature, pressure, and oxygen.
3.18
peripheral SRM
SRM used to gather the data required to convert the SRM measured values to AMS or standard conditions
Note 1 to entry: A peripheral SRM is used to measure water vapour, temperature, pressure, and oxygen.
3.19
precision
closeness of agreement of results obtained from the AMS for successive zero readings and successive
span readings at defined time intervals
3.20
reference material
substance or mixture of substances with a known concentration within specified limits, or a device of
known characteristics
Note 1 to entry: Normally used are calibration gases, gas cells, gratings, or filters.
3.21
response time
t90
time interval between the instance 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
Note 1 to entry: The response time is also referred to as the 90 % time.
3.22
span reading
instrument reading of the AMS for a simulation of the input parameter at a fixed elevated concentration.
This simulation should test as much as possible all the measuring elements of the system, which
contribute significantly to its performance.
Note 1 to entry: The span reading is approximately 80 % of the measured range.
3.23
standard conditions
conditions as given in legislation to which measured values have to be standardized
3.24
standard deviation
positive square root of the mean squared deviation from the arithmetic mean, divided by the degrees
of freedom
Note 1 to entry: The number of degrees of freedom is the number of measurements minus 1.
3.25
Standard Reference Method
SRM
method described and standardised to define a measurand, temporarily conducted on site for verification
purposes
Note 1 to entry: Also known as a reference method.
3.26
uncertainty
parameter associated with the result of a measurement that characterises the dispersion of the values
[5]
that could reasonably be attributed to the measurand
3.27
variability
standard deviation of the differences of parallel measurements between the SRM and AMS
3.28
zero reading
instrument reading of the AMS on simulation of the input parameter at zero concentration, which shall
test as much as possible all the measuring elements of the AMS, that contribute significantly to its
performance
4 © ISO 2014 – All rights reserved
4 Symbols and abbreviations
4.1 Symbols
a intercept of the calibration function
â best estimate of a
b slope of the calibration function
ˆ best estimate of b
b
D difference between SRM value y and calibrated AMS measured value ŷ
i i i
average of D
i
D
E maximum value of measuring range
k test value for variability (based on a χ -test, with a β-value of 50 %, for N numbers of paired measure-
v
ments)
N number of paired samples in parallel measurements
σ standard deviation of the differences D in parallel measurements
i
t value of the t distribution for a significance level of 95 % and a number of degrees of freedom of N – 1
0,95; N–1
u uncertainty due to instability (expressed as a standard deviation)
inst
u uncertainty due to influence of temperature (expressed as a standard deviation)
temp
u uncertainty due to influence of pressure (expressed as a standard deviation)
pres
u uncertainty due to influence of voltage (expressed as a standard deviation)
volt
u any other uncertainty that can influence the zero and span reading (expressed as a standard devia-
others
tion)
th
x i measured signal obtained with the AMS at AMS measuring conditions
i
x average of AMS measured signals x
i
th
y i measured value obtained with the SRM
i
y
average of the SRM measured values y
i
y SRM measured value y at standard conditions
i,s i
y lowest SRM measured value at standard conditions
s,min
y highest SRM measured value at standard conditions
s,max
ŷ best estimate for the “true value”, calculated from the AMS measured signal x by means of the cali-
i i
bration function
ŷ best estimate for the “true value”, calculated from the AMS measured signal x at standard conditions
i,s i
ŷ best estimate for the “true value”, calculated from the maximum value of the AMS measured signals x
s,max i
at standard conditions
Z offset (the difference between the AMS zero reading and the zero)
s standard deviation of the AMS used in ongoing quality control
AMS
α significance level
ԑ deviation between y and the expected value σ standard deviation associated with the uncertainty
i i 0
derived from requirements of legislation
4.2 Abbreviations
AMS automated measuring system
AST annual surveillance test
QA quality assurance
SRM Standard Reference Method
5 Principle
5.1 General
An AMS to be used shall be proven suitable for its measuring task (parameter and composition of the flue
gas) by use of the procedures specified in ISO 14956. Using this part of ISO 14385, it shall be proven that
the total uncertainty of the results obtained from the AMS meets the specification for uncertainty stated
in legislation or in requirements and specifications established in an international trading program. In
ISO 14956, the total uncertainty required by the relevant regulations is calculated by summing all the
relevant uncertainty components arising from the individual performance.
This part of ISO 14385 provides a procedure for the validation and calibration of an AMS. It consists
of the determination of the calibration function and its variability, and a test of the variability of the
measured values of the AMS compared with the uncertainty given by legislation or in requirements and
specifications established in international trading programs. The tests are based on a number of parallel
measurements performed with a Standard Reference Method (SRM). The variability of the measured
values obtained with the AMS can then be evaluated against the maximum permissible uncertainty.
The tests are performed on AMS that have been correctly installed and commissioned.
The tests can be used to
a) establish a calibration function over a range of plant operating conditions and
b) calibrate the AMS and demonstrate that an AMS meets the required accuracy at a constant operating
load.
The procedure is repeated periodically after a major change of plant operation, after a failure of the
AMS, or as required by legislation.
5.2 Limitations
Figure 2 illustrates the components of the AMS covered by this part of ISO 14385.
6 © ISO 2014 – All rights reserved
Figure 2 — Limits for the QA of the AMS excluding the data acquisition and handling system
NOTE 1 The influence of the uncertainty of the measurement results, which arise from the data acquisition
recording and handling system of the AMS or of the plant system and its determination, are excluded from this
part of ISO 14385.
NOTE 2 The performance of the data collection and recording system can be as influential as the AMS
performance in determining the quality of the results obtained from the whole measuring system/process. There
are different requirements for data collection recording and presentation in different countries.
When conducting parallel measurements, the measured signals from the AMS are taken directly from
the AMS (e.g. expressed as analogue or digital signal) during the calibration and annual surveillance test
(AST) procedures specified in this part of ISO 14385 by using an independent data collection system
provided by the organization(s) carrying out the calibration and AST tests, as specified in ISO 14385-2.
All data shall be recorded in their uncorrected form (without corrections for, e.g. temperature and
oxygen). A plant data collection system with quality control can additionally be used to collect the
measured signal from the AMS.
5.3 Measurement site and installation
The AMS shall be installed in accordance with the requirements of the relevant national or international
standards, as specified by legislation, competent authorities, or in emission trade scheme. Special
attention shall be given to ensure that the AMS is readily accessible for regular maintenance and other
necessary activities.
NOTE The AMS is intended to be positioned as far as practical so that it measures a sample representative of
the stack gas composition.
All measurements shall be carried out on a suitable AMS and peripheral AMS installed within an
appropriate working environment.
The working platform used to access the AMS shall readily allow parallel measurements to be performed
using an SRM. The sampling ports for measurements with the SRM shall be placed as close as possible,
but not more than three times the equivalent diameter up- or down-stream of the location of the AMS,
in order to achieve comparable measurements between AMS and SRM.
It is necessary to have good access to the AMS to enable inspections to take place and also to minimize
time taken to implement the quality assurance procedures of this part of ISO 14385. A clean, well-
ventilated, and well-lit working space around the AMS is required to enable the staff to perform this
work effectively. Suitable protection is required for the personnel and the equipment, if the working
platform is exposed to the weather.
5.4 Testing laboratories performing SRM measurements
The testing laboratories, which perform the measurements with the SRM, shall be accredited for this
task according to ISO/IEC 17025 or shall be approved directly by the relevant competent authority.
6 Calibration and validation of the AMS
6.1 General
Testing shall cover the following items:
— installation of the AMS;
— functional test of the AMS;
— calibration of the AMS by means of parallel measurements with an SRM and, if necessary, in
combination with calibration gases;
— validation of the AMS (determination of the variability of the AMS and the check of compliance with
the maximum permissible uncertainty or determination of the relative uncertainty).
A calibration procedure shall be performed for all measurands at least every 5 years for every AMS
and more frequently if so required by legislation, requirements, and specifications established in an
international trading program or the competent authority.
Furthermore, a calibration procedure shall be performed for all the measurands influenced by
— any major change in plant operation (e.g. change in flue gas abatement system or change of fuel) or
— any major changes or repairs to the AMS, which will influence the results obtained significantly.
The results of the calibration procedure shall be reported within 6 months after the changes. During the
period before a new calibration function has been established, the previous calibration function (where
necessary with extrapolation) shall be used.
The measurement range shall be chosen to ensure the expected measurement values are between 25 %
and 75 % of the maximum of this range.
6.2 Functional test
The requirements for installation and the measurement site as specified in 5.3 shall be checked.
If peripheral AMS is used to convert the measured values to other conditions, these AMS shall be subject
of functional tests.
NOTE Since the AMS and SRM measured values are converted to other conditions by independently
determined data sets of the peripheral parameters, the uncertainties in the peripheral parameters are attributed
to the AMS of the air pollutant in the variability test.
The functional test before calibration shall be performed according to Annex A. The period between the
functional test and the calibration shall be limited to 1 month.
The specific precautions to be taken should depend on the individual location.
6.3 Calibration and validation of multiple/complex measurement systems
Although the procedures in this part of ISO 14385 are primarily describing the calibration and
validation of single instruments, the same procedures can be used for the calibration and validation
of multiple/complex measurement systems. For instance, in many countries, emission limit values are
expressed in concentrations at standard conditions (dry flue gas with temperature 273,15 K, pressure
8 © ISO 2014 – All rights reserved
1013 hPa, and a specified oxygen concentration). In such a case, the measurement system consists of
several analysers and measuring devices (peripheral AMS) (analyser for air-polluting compound, oxygen
analyser, measuring devices for temperature, pressure, and water vapour).
If legislation or requirements and specifications established in an international trading program are
requiring calibration and validation of concentrations of air-polluting compounds at standard conditions,
two options are possible.
First, this can be realized by calibration of the results of the individual analysers and measuring devices
using the measurement results of the appropriate reference methods for each of the components in the
calculation (air-polluting compound, oxygen, temperature, pressure, and water vapour). The calibrated
results are then used for conversion by calculation to concentrations at standard conditions.
Alternatively, the results of the individual analysers and measuring devices are converted to standard
conditions and then calibrated to the converted results of the reference methods.
The standard deviation used in the validation procedure has to be calculated by using Formula (11) and
on the basis of the normalized calibrated AMS values and the normalized SRM values.
6.4 Parallel measurements with an SRM
Parallel measurements shall be performed with the AMS and SRM in order to calibrate and/or validate
the AMS by use of an independent method.
It is not sufficient to use reference materials alone to obtain the calibration functions and this is therefore
not permitted. This is because these reference materials do not replicate sufficiently the matrix stack
gas, they cannot be used to establish that the sampling point(s) of the AMS are representative, and
they are not used with the sampling system in all cases. However, if there are limited variations in the
results obtained in the AMS/SRM tests, and the measured concentrations are more than 20 % below
the maximum value of the normal measuring range, an extrapolation of the calibration function to the
highest annual value can be verified by the use of appropriate reference materials, taking into account
the effects of interfering substances on the AMS, where appropriate.
If clear and distinct operating modes of the plant process are part of its normal operation (for example,
changes of fuel), additional calibrations shall be performed and a calibration function established for
each operational mode if the operation affects the calibration curve.
NOTE 1 It is recommended that a preliminary test be carried out in order to evaluate if a full calibration over
the whole concentration range can be performed. Otherwise, a competent authority is intended to judge if, based
on its experience, it is reasonable to establish one calibration function that covers all normal changes in the
process.
In order to ensure that the calibration function is valid for the range of conditions within which the plant
will operate, the concentrations during the calibration shall be varied as much as possible within the
normal operations of the plant. This shall ensure that the calibration of the AMS is valid over as large a
range as possible, and also that it covers most operational situations.
The test for variability shall be performed (see 6.5.6) for each calibration function, i.e. for each operating
mode of the plant.
An SRM shall be used to measure the emissions through representative sampling in the duct, which is
as close as possible to the AMS. The sampling of the AMS and SRM shall not influence the results of both
measurement systems.
The presence of the equipment specified in the SRM shall not influence or disturb the AMS measurements.
For each calibration, a minimum of 15 valid parallel measurements shall be made with the plant
operating normally. These measurements shall be uniformly spread both over at least 3 d and over each
of the measuring days of normally 8 h to 10 h (e.g. not five measurements in the morning and none in the
afternoon) and be performed within a period of 4 weeks.
NOTE 2 The required spread of a minimum of 15 valid measurements over 3 d is essential in minimising the
effect of influences of the subsequent measurement results (i.e. to avoid auto-correlation between the calculated
differences in the results of the AMS and SRM). The alternative of performing more measurements within a
shorter time interval can lead to the establishment of an invalid calibration function.
NOTE 3 A minimum of 15 valid measurements can, in practice, require that more than 15 samples be taken,
since some samples can be deemed to be invalid during subsequent analysis because of inadequate quality.
NOTE 4 The requirement that the measurements need to be uniformly spread over at least 3 d does not imply
that the measurements need to be performed within three consecutive days.
If the calibration is not the first calibration being carried out on the AMS and the operator can prove
that at least 95 % of the AMS measured values obtained since the last calibration or annual surveillance
test (see ISO 14385-2) are less than the maximum permissible expanded uncertainty, the number of
measurements can be reduced to five parallel measurements performed on 1 d. The results of these five
measurements shall be used to check the validity of the existing calibration function. If the calibration
function appears not to be valid, the number of parallel measurements shall be increased to 15 parallel
measurements to calculate a new calibration function.
Examples of expanded uncertainty are given in Annex F.
A set of measurements is valid when all of the requirements below are fulfilled:
— the SRM measurements are performed according to the accepted standard;
— the time period of each AMS measured signal shall cover at least 90 % of the averaging time
[excluding all of the measured signals which are above 100 % or below 0 % of the measuring range
of the AMS, signals obtained during internal checks (auto calibration), and signals obtained during
any other malfunctioning of the AMS].
During the parallel measurements with the AMS and SRM, each result is considered as a measurement
pair (one AMS measured signal and one SRM measured value) and these shall cover the same time period.
The sampling time for each of the parallel measurements shall be at least 30 min, or at least four times
the response time of the AMS, including the sampling system (as determined during the response time
measurements carried out during the procedures according to ISO 14956), whichever is the greater. In
general, the sampling time should equal the shortest averaging time, which is required by the legislation
or as defined in an international trading program. The recording system shall have an averaging time
significantly shorter than the response time of the AMS.
If the sampling time is shorter than 1 h, then the time interval between the start of each sample shall be
longer than 1 h.
The results obtained from the SRM shall be expressed under the same conditions as measured by the
AMS (e.g. conditions of pressure, temperature, etc.). In order to establish the calibration function and
perform the variability test, all additional parameters and values included in the corrections to AMS
conditions and standard conditions shall be obtained for each measurement pair.
EXAMPLE If the AMS measures N O in units of mg/m in stack gas containing water vapour, then the SRM
results are expressed in the same units (e.g. mg/m in the stack gas with the same water vapour concentration).
The 15 parallel measurements can be performed in less than 3 d if
— at least 97 % of the validated half-hourly values obtained in the period since the last calibration
were smaller than 30 % of the measurement range value specified for half-hourly values or
— at least 99 % of the validated half-hourly values obtained in the period since the last calibration do
not deviate from the average of all validated half-hourly values by more than 5 %.
In these cases, the interval between the start of each sampling can be less than 1 h.
10 © ISO 2014 – All rights reserved
In order to fulfil the requirement that the calibration of the AMS is valid over as large a range as possible,
and that it covers most operational situations, parallel measurements over 3 d are generally required.
However, this can require several manual SRM measurements of the water vapour concentration. If
calibrated AMS measured values for water vapour are available, these can be used to convert the SRM
data to dry or wet basis. When wet abatement techniques are used, the water vapour concentration is
often nearly constant and extended measurement of the water vapour concentration is of little purpose.
In those situations, conversion of SRM data to dry or wet basis as required can be carried out using
calculated AMS water vapour measurements.
6.5 Procedure: calibration and validation of the AMS by means of parallel measure-
ments
6.5.1 General
In this procedure, the calibration function of the AMS and its variability are determined by means of
parallel measurements with an SRM. The variability of the measured values obtained with the AMS is
then evaluated against the maximum permissible uncertainty.
The sequence of the tests to be carried out is shown in Figure 3.
See 6.4
See 6.5.2
See 6.5.3
See 6.5.5
See 6.5.6
See 6.6
Figure 3 — Flow diagram for the calibration and variability tests
Examples of calculation of the calibration function and of the variability test are given in Annex D.
NOTE If change in fuel mixture is a part of the normal operation mode of the plant, it is recommended that
the fuel mixture is varied during the parallel measurements.
6.5.2 Data evaluation
6.5.2.1 Preparation of data
The steps for providing data required for establishing the calibration function and performing the test
of variability are illustrated in Figure 4.
6.5.2.2
NOTE The figure in the circles indicates the sequence of the steps.
Figure 4 — Flow chart describing the steps in calibration procedure and test for variability
The AMS shall be calibrated at the condition of the exhaust gas as measured by the AMS. Therefore, the
SRM values shall be converted to AMS measuring conditions, if necessary, giving SRM measured values,
y , to be expressed in concentration units (e.g. mg/m ).
m
The measured signals from the AMS, x can be either a signal in an electrical unit (e.g. mA or Volt) or in a
i
concentration unit (e.g. mg/m ).
NOTE For a non-extractive AMS that measures the gas directly, the calibration function reported shall be
at the operating conditions. For an extractive AMS measuring at specified conditions, the calibration function is
reported at these specified conditions.
The data sets obtained in the parallel measurements shall be checked for possible outliers (see Annex E).
The method used to assess outliers and reasons for excluding outliers shall be given in the calibration
report. Outliers shall be reported and identified in the calibration diagrams. This part of ISO 14385
requires at least 15 valid data points for a calibration function. If points are excluded, e.g. through the
use of outlier tests, this requirement can be failed. It is therefore recommended that additional data
points be taken, to allow for the exclusion of outliers. If this is not done, the calibration can be invalid.
12 © ISO 2014 – All rights reserved
6.5.2.2 Establishing the calibration function
It is presupposed in this part of ISO 14385 that the calibration function is linear and has a constant
residual standard deviation. The calibration function shall be described by Formula (1) [ISO 11095]:
ya=+bx +ε (1)
ii i
where
th
x is the i result of the AMS; i = 1 to N; N ≥ 15;
i
th
y is the i result of the SRM; i = 1 to N; N ≥ 15;
i
ε is the deviation between y and the expected value;
i i
a is the intercept of the calibration function;
b is the slope of the calibration function.
The general procedure [Formula (4) and (5)] requires a sufficient range of the measured concentrations
to give a valid calibration of the AMS for the complete range of concentrations encountered during normal
operation. As stated in 6.5, it is essential that the concentration range is as large as possible within the
normal operation of the plant for a valid calibration function. However, at a large number of plants, it
can be difficult under normal operating conditions to achieve a sufficiently large concentration range.
In such cases, in which the concentration range (measured with the SRM) is less than the maximum
permissible uncertainty, another (similar) procedure is given below (procedure b).
NOTE 1 If the concentration range is slightly bigger than maximum permissible uncertainty, and if Formulae (4)
and (5) result in an inadequate calibration function (e.g. a function with negative slope), Formulae (6) and (7) can
be used instead.
Formulae (2) and (3) shall be calculated:
N
x= x (2)
∑ i
N
i=1
N
y= y (3)
∑ i
N
i=1
The difference ( y – y ) between the highest and lowest measured SRM concentration at standard
s,max s,min
conditions shall be calculated.
a) If (y – y ) is greater than or equal to the maximum permissible uncertainty, calculate:
s,max s,min
N
()xx−−yy
()
∑
ii
i=1
ˆ
b = (4)
N
()xx−
∑
i
i=1
ˆ
ây= - bx (5)
b) If (y – y ) is smaller than the maximum permissible uncertainty, calculate:
s,max s,min
y
ˆ
b = (6)
xZ−
ˆ
âb=− ×Z (7)
where the offset (Z) is the difference between the AMS zero reading and the zero.
NOTE 2 For several AMS, the offset is 4 mA.
For calculation b), it is essential that, prior to the parallel measurements, it is proven that the AMS gives
a reading at, or below, detection limit (as demonstrated in the procedures according to ISO 14956) at
a zero concentration. Before calibration is performed, it shall be proven that the AMS is commissioned
satisfactorily, e.g. as specified by the AMS supplier and/or manufacturer. It shall also be shown and
documented that the AMS gives a zero reading on a zero concentration (as stated in 6.2).
If the spread of the data is less than the maximum permissible uncertainty, a calibration function
calculated as a linear regression function forced through the lower reference point (which is the zero
point if the AMS reads zero) can be used, provided the functional test has proven that it is linear down
to the lower reference point or zero.
The results shall be plotted on an x-y graph in order to show explicitly the calibration function and the
valid calibration range.
6.5.2.3 Low-level clusters
There are typically three types of patterns of emissions from industrial plants; in addition to the patterns
of data described in 6.5.2.2 and assessed using procedure a or procedure b, the emissions can be very
low, clustered at, or near to zero. Low-level clusters are often the result of highly controlled processes,
and are common for N O and CH emissions from most combustion plants.
2 4
If y – y is smaller than the maximum permissible uncertainty and y is smaller than the
s,max s,min s,min
maximum permissible uncertainty (low-level clusters), then the uncertainties of both the SRM and AMS
can undermine the accuracy of the calibration function. Therefore, if the low-level condition is met, then
it is advisable to contact the competent authority for guidance on an alternative procedure.
Alternative procedures include the following three options:
— Option 1: Performing a calibration as specified in Clause 6, applying procedure b, and accepting that
the uncertainty of the measurements can introduce a significant calibration error.
— Option 2: Performing a limited number of measurements using the SRM, perhaps over 1 d instead
of at least 3 d. The purpose of the SRM measurements is to ensure that the emissions are as low as
the AMS shows. The AMS is then calibrated using surrogates, such as reference materials with a low
uncertainty. This approach can have a high uncertainty, but again, this error will not be significant
if the emissions remain well below the maximum value of the lowest measuring range.
— Option 3: As with opt
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