IEC 61757-2-2:2016

IEC 61757-2-2 ®
Edition 1.0 2016-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic sensors –
Part 2-2: Temperature measurement – Distributed sensing

Capteurs à fibres optiques –
Partie 2-2: Mesure de température – Détection répartie

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IEC 61757-2-2 ®
Edition 1.0 2016-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic sensors –
Part 2-2: Temperature measurement – Distributed sensing

Capteurs à fibres optiques –
Partie 2-2: Mesure de température – Détection répartie

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.99 ISBN 978-2-8322-8787-3

– 2 – IEC 61757-2-2:2016 © IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 General test setups for measurement of performance parameters . 11
4.1 General and test setup requirements . 11
4.2 General required information to be documented . 13
5 Measurement procedures for performance parameters . 14
5.1 Temperature measurement error . 14
5.1.1 Test procedure and conditions . 14
5.1.2 Parameter calculation . 14
5.2 Spatial resolution . 16
5.2.1 Test procedure and conditions . 16
5.2.2 Parameter calculation . 16
5.3 Temperature repeatability . 17
5.3.1 Test procedure and conditions . 17
5.3.2 Parameter calculation . 17
5.3.3 Formulas . 18
5.4 Spatial temperature uncertainty . 19
5.4.1 Test procedure and conditions . 19
5.4.2 Parameter calculation . 19
5.5 Environmental temperature stability . 20
5.5.1 Test procedure and conditions . 20
5.5.2 Parameter calculation . 21
5.6 Warm-up time . 22
5.6.1 Test procedure and conditions . 22
5.6.2 Parameter calculation . 23
5.7 Attenuation range . 24
5.7.1 Test procedure and conditions . 24
5.7.2 Parameter calculation . 25
Annex A (informative) Measurement parameter performance table . 26
Annex B (informative)  Point defect effects . 28
B.1 General . 28
B.2 Point defect . 28
B.3 Test procedures and conditions . 28
Bibliography . 31

Figure 1 – Example of a temperature trace with temperature sample points . 10
Figure 2 – General test setup: single-ended . 12
Figure 3 – General test setup: loop configuration . 12
Figure 4 – Temperature measurement error calculation: step 1 . 15
Figure 5 – Temperature measurement error calculation: steps 2 through 3 . 15
Figure 6 – Temperature measurement error calculation: steps 4 through 5 . 16

Figure 7 – Spatial resolution illustration . 17
Figure 8 – Temperature repeatability calculated from Figure 4 . 18
Figure 9 – Spatial temperature uncertainty calculated from Figure 4 . 20
Figure 10 – Environmental temperature cycle (example for a DTS instrument with an
operating temperature range of 0 °C to 40 °C) . 21
Figure 11 – Environmental temperature stability parameter calculation method . 22
Figure 12 – Example illustrating calculation of warm-up time . 23
Figure B.1 – Point defect measurement (example) . 29

Table A.1 – Blank measurement parameter performance table . 26

– 4 – IEC 61757-2-2:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC SENSORS –
Part 2-2: Temperature measurement – Distributed sensing

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61757-2-2 has been prepared by subcommittee SC 86C: Fibre optic
systems and active devices of IEC technical committee 86: Fibre optics.
The text of this standard is based on the following documents:
CDV Report on voting
86C/1323/CDV 86C/1354/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 61757 series, published under the general title Fibre optic sensors,
can be found on the IEC website.
This International Standard is to be used in conjunction with IEC 61757-1:2012.

The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 6 – IEC 61757-2-2:2016 © IEC 2016
INTRODUCTION
It has been decided to restructure the IEC 61757 series with the following logic. From now on,
the sub-parts will be renumbered as IEC 61757-M-T where M denotes the measure and T the
technology.
The existing part IEC 61757-1:2012 will be renumbered as IEC 61757 when it will be revised
and will serve as an umbrella document over the entire series.

FIBRE OPTIC SENSORS –
Part 2-2: Temperature measurement – Distributed sensing

1 Scope
This part of IEC 61757 defines detail specifications for distributed temperature measurement
by a fibre optic sensor, also known as fibre optic distributed temperature sensing (DTS). DTS
includes the use of Raman scattering, Brillouin scattering and Rayleigh scattering effects. In
addition, Raman scattering and Rayleigh scattering based measurements are performed with a
single-ended fibre configuration only. Brillouin scattering based measurements are performed
with a single-ended fibre or fibre loop configuration. The technique accessible from both sides
at same time (e. g. Brillouin optical time domain analysis, BOTDA) is referred to here as a loop
configuration. Generic specifications for fibre optic sensors are defined in IEC 61757-1:2012.
This part of IEC 61757 specifies the most important DTS performance parameters and defines
the procedures for their determination. In addition to the group of performance parameters, a
list of additional parameters has been defined to support the definition of the measurement
specifications and their associated test procedures. The definitions of these additional
parameters are provided for informational purposes and should be included with the sets of
performance parameters.
A general test setup is defined in which all parameters can be gathered through a set of tests.
The specific tests are described within the clause for each measurement parameter. This
general test setup is depicted and described in Clause 4 along with a list of general information
that should be documented based upon the specific DTS instrument and test setup used to
measure these parameters as per IEC 61757-2-2.
Annex A provides a blank performance parameter table which should be used to record the
performance parameter values for a given DTS instrument and chosen optical test setup
configuration.
Annex B provides guidelines for optional determination of point defect effects.
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.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
http://www.electropedia.org)
IEC 61757-1:2012, Fibre optic sensors – Part 1: Generic specification
IEC TR 61931, Fibre optic – Terminology
ISO/IEC Guide 99, International vocabulary of metrology – Basic and general concepts and
associated terms (VIM)
– 8 – IEC 61757-2-2:2016 © IEC 2016
3 Terms and definitions
For the purposes of this document, the definitions given in IEC 61757-1:2012, IEC 60050,
IEC TR 61931, ISO/IEC Guide 99 (VIM), as well as the following apply.
3.1
attenuation range
total cumulated optical loss (one way loss) tolerated by the DTS system without affecting the
specified measurement performance more than a given factor at a given location, spatial
resolution, and measurement time
Note 1 to entry: Part of the total cumulative loss can be the fibre attenuation, point defect losses introduced by
components such as connectors, splices, kink in the fibre, attenuators.
Note 2 to entry: The attenuation range is expressed in decibels (dB).
3.2
distance measurement range
maximum distance from the DTS instrument output connector along the fibre optic sensor within
which the instrument measures a temperature with specified measurement performance under
defined conditions
Note 1 to entry: This supporting parameter is closely related to the attenuation range of the instrument. In test
cases used to prove or verify the reported specifications, the total fibre length shall be equal to or greater than the
specified distance measurement range.
Note 2 to entry: The distance measurement range is expressed in length units (m or km).
3.3
environmental temperature repeatability
difference of the measured constant fibre optic sensor temperature at a specified instrument
temperature (e. g. nominal operating temperature) before and after temperature cycling of the
instrument across the entire instrument operating temperature range
Note 1 to entry: This parameter is derived from environmental temperature stability.
3.4
environmental temperature stability
difference of the measured constant fibre optic sensor temperature before, during and after
temperature cycling of the DTS instrument across the entire instrument operating temperature
range
Note 1 to entry: Worst case environmental temperature effect, high/low environmental temperature effect, and
environmental temperature repeatability are derived from this definition.
3.5
high/low environmental temperature effect
difference of the measured constant fibre optic sensor temperature at the high and low
temperature limit of the instrument temperature operating range
Note 1 to entry: This parameter is derived from environmental temperature stability.
3.6
hot spot
length of fibre optic sensor (∆L) which is exposed by a measurable temperature change (∆T)
which is significantly bigger than the instrument temperature repeatability and which is
confirmed by reference temperature devices in the two thermal chambers.
Note 1 to entry: See Clause 4 and Figure 7.

3.7
L
location
optical distance (specified in length units) from the DTS instrument output connector to a
desired temperature sample point along the fibre optic sensor
Note 1 to entry: The furthest location from DTS instrument output connector for the particular test is quantified as
Z m and is often chosen to be the same as the distance measurement range for purposes of comparing the
measurement results with quoted specifications.
3.8
measurement time
time between independent temperature measurements when making successive measurements
on a single fibre optic sensor
Note 1 to entry: This parameter includes acquisition time and processing time for measured data. This parameter
is selectable by the user typically in some limited fashion. Multiple independent temperature measurements may be
averaged together to provide an overall measurement time.
Note 2 to entry: Equivalently, it is the time interval between successive temperature trace timestamps under these
conditions.
3.9
point defect
local deviation of a fibre optic sensor from its nominal optical and mechanical properties
occurring at a single location, or over a length substantially less than the DTS spatial resolution
Note 1 to entry: The definition of a point defect encompasses a wide range of situations, which may produce similar
effects on the temperature trace. Examples include
– a point loss, such as a bad fibre splice;
– a back reflection, such as may arise from a fibre connector;
– a localized region of high loss, such as a bend or kink in the fibre;
– a physical discontinuity in the fibre, such as a splice between two fibres of different core diameters.
3.10
point defect temperature offset
difference between the average values of the temperature sample points in two zones on the
temperature trace, one each side of a point defect, where the actual fibre optic sensor
temperatures are the same
Note 1 to entry: The point defect temperature offset may be positive, negative or zero.
3.11
sample spacing
distance between two consecutive temperature sample points in a single temperature trace
Note 1 to entry: See Figure 1.

– 10 – IEC 61757-2-2:2016 © IEC 2016
Red dots represent Black line represents
temperature sample points the actual temperature (unknown)
Sample
spacing
Location (m)
IEC
Figure 1 – Example of a temperature trace with temperature sample points
Note 2 to entry: Sample spacing may be a user-selectable instrument parameter.
Note 3 to entry: The distance measurement range is expressed in length units (in m).
Note 4 to entry: In case of very high spacing resolution, the distance measurement range can be expressed in cm
or mm.
3.12
spatial resolution
smallest length of a temperature-affected fibre optic sensor for which a DTS system can
measure the reference temperature of the hot spot fibre condition within the specified
temperature measurement error of the DTS system
3.13
spatial temperature uncertainty
uncertainty of location of temperature data in a single temperature trace expressed by twice the
standard deviation of a specified number of adjacent temperature sample points, with the fibre
optic sensor held at constant temperature
3.14
temperature dead zone
limited zone of a temperature trace, where the temperature sample points deviate from the
undisturbed parts of the trace by a specified limit due to a point defect
3.15
temperature measurement error
maximum difference between a centred and uniformly weighted moving average of the
measured temperature and a reference temperature for all data points of the fibre optic sensor
over the full operating temperature range and all acquisition times
Note 1 to entry: Single value (worst case) is specified in temperature units (e.g. ± 0,8 °C).
Note 2 to entry: The number of elements used for the moving average is defined in Clause 5. In practical
applications, other methods of smoothing might be applicable.
3.16
temperature repeatability
precision of temperature data based on repeated temperature traces at a given location
expressed by twice the standard deviation of corresponding temperature sample points in each
temperature trace, with the fibre optic sensor held at constant temperature
Temperature (°C)
3.17
temperature sample point
measured temperature value associated with a single point at a known location along a fibre
optic sensor
Note 1 to entry: Due to thermodynamic effects, the measured value represents the temperature along a very small
section of the fibre optic sensor that includes the point.
3.18
temperature trace
set of temperature sample points distributed along a fibre optic sensor and spaced by the
sample spacing
Note 1 to entry: All the sample points are associated with a common time of measurement, often called the trace
timestamp. The measured values represent the temperature during a period that includes the timestamp.
Note 2 to entry: All the sample points in a temperature trace are measured values produced by the DTS instrument,
and not interpolated or smoothed values produced by subsequent processing outside the instrument.
3.19
Z
total fibre length
distance from the DTS output connector to the final end of the fibre optic sensor
Note 1 to entry: Final end of the fibre optic sensor can either be a purposefully cut or terminated end of the fibre
physically far from the instrument (in a single-ended configuration), or the end of a loop consisting of a connector
that is connected to the same instrument (in a loop configuration).
Note 2 to entry: This parameter is either equal to or greater than the distance measurement.
Note 3 to entry: The distance measurement range is expressed in length units (m or km).
3.20
warm-up time
duration of time starting from the initiation of the first temperature measurement until the DTS
instrument complies with specified measurement specifications
3.21
worst case environmental temperature effect
maximum difference of the measured constant fibre optic sensor temperature at different
locations along the sensor during a complete temperature cycling of the DTS instrument across
the entire instrument operating temperature range
Note 1 to entry: This parameter is derived from environmental temperature stability.
4 General test setups for measurement of performance parameters
4.1 General and test setup requirements
General test setups for single and loop configurations are schematically shown in Figure 2 and
Figure 3 respectively. Their aim is to provide a common base for determining the measurement
specifications while at the same time minimizing complexity, cost, reconfiguration requirements,
and test execution time.
– 12 – IEC 61757-2-2:2016 © IEC 2016
Chamber @
Chamber @
(T , T , T ) °C
operat op-min op-max
(T , T , T ) °C
1 2 3
X
C A
X X
DTS
instrument C
B
D D
X X
C
C
Chamber @ Chamber @
W
Y °C
≤ (Y – 20) °C
VOA (variable optical attenuator
Connector
(only present for attenuation range)

X fibre fusion splice
Y hot spot temperature (°C)
D fibre length (m); loose wound
A fibre length (m) < spatial resolution
B fibre length (m) = claimed spatial resolution
W fibre length (m); normal spool
C fibre length (m) > 4 × spatial resolution
Short coil of fibre; loose wound
IEC
Figure 2 – General test setup: single-ended
Chamber @
Chamber @
(T , T , T ) °C
1 2 3
(T , T , T ) °C
operat op-min op-max
X
C A
X
DTS X
D
D
instrument C
B
X
X
W or (W/2)
C
C
X
Chamber @ Chamber @
≤ (Y – 20) °C Y °C
W or (W/2)
VOA (variable optical attenuator
Connector
(only present for attenuation range)

X fibre fusion splice
Y hot spot temperature (°C)
D fibre length (m); loose wound
A fibre length (m) < spatial resolution
B fibre length (m) = claimed spatial resolution
W fibre length (m); normal spool
C fibre length (m) > 4 × spatial resolution
Short coil of fibre; loose wound
IEC
Figure 3 – General test setup: loop configuration
Individual evaluation procedures may be performed with a modified type of setup providing the
required measurement conditions. In this case, a detailed setup description and documentation
is required.
The fibre lengths A, B, C of the fibre coils in the thermal chambers at the end of the setup shall
be selected based upon the expected spatial resolution of the DTS system. The fibre lengths D
and W within and outside the centre chamber shall be chosen to make the total fibre length Z
match the distance measurement range of the particular DTS model being tested. The use of
fibre length D, located before and after a long length W of fibre (which makes up the total fibre
length Z), provides a test setup capable of accommodating various instruments with different
distance measurement ranges. Fibre length D shall be equal to 10 % of the total fibre length Z.

However, the use of a length of fibre outside the central chamber is optional – all fibre may be
contained within the chamber, if desired, as single or multiple coils. The total fibre length Z is
equal to the total length of fibre from the instrument connector up to the end of the spatial
resolution fibre section represented by fibre lengths A, B, C.
A symmetric test setup represents the normal field operation setup. This is reflected by the test
setup described in Figure 3. Fibre length W makes up the total fibre length Z. In case of a system
comparison with a single-ended test setup, the length of the normal spools shall be (2 × W/2).
This guarantees the same overall attenuation. In all other cases the length of the normal spools
shall be (2 × W).
Fusion splices should be used for fibre connection to minimize additional optical losses and
unwanted back-reflections. Low insertion loss and back-reflections shall be accomplished when
connecting the fibres by connectors.
The fibres in the chambers shall be coiled in such a way (loose wound) that the fibre is
completely exposed by the surrounding temperature, and that there is no fibre strain. Normal
spool in this case means a fibre spool as delivered from the fibre supplier.
It shall be noted that the general test setup provides a schematic diagram only. The real
implementation may differ in certain respects, such as replacing any of the fibre containing
chambers with liquid filled calibration baths or replacing the double chamber with an alternative
implementation that provides a large and sharp enough temperature difference between the
coils (at least 20 °C occurring over no longer than 50 % of the rated spatial resolution).
It is required that the uncertainty of the reference temperature measurement is at least a factor
of 5 smaller than the temperature measurement error that is being assessed. Such reference
temperature sensors are not shown in the setup diagrams but are required to be present and
properly calibrated within each temperature chamber and/or bath.
Setting requirements on the homogeneity or stability of the chambers or the sharpness of the
realized temperature step is not necessary. Failure to realize these test setup qualities at a
sufficient level will only produce measurement data that is more conservative (worse
performance).
The DTS instrument-under-test shall be calibrated according to manufacturer’s
recommendations before performing any measurements.
4.2 General required information to be documented
The general required information to be documented is as follows:
• completion date of all testing;
• name of the organization executing the testing;
• test setup configuration;
• operating mode of the DTS instrument (single-ended or loop configuration as shown in
Figures 2 and 3, or channel(s) tested in case of a multi-channel system using the same
hardware);
• wavelength(s) of the launched signals (operating wavelength(s));
• manufacturer, model, and serial number of the DTS instrument;
• manufacturer, model, and length of the fibre optic sensor in the test setup (inside the
temperature chamber(s));
• optical loss (one-way in dB) of the optical setup to the end of the sensor (Z m);
• wavelength used to measure the loss to end of the sensor (Z m);
• distance measurement range of the DTS instrument;

– 14 – IEC 61757-2-2:2016 © IEC 2016
• sample spacing used for all measurements;
• spatial resolution setting used for all measurements;
• measurement time used during DTS instrument calibration;
• lengths of fibre coils A, B,C and D and spool(s) W;
• nominal temperatures of both parts of the double-chambers in °C;
• maximum (hot) and minimum (cold) operating temperature limits (°C) of the DTS instrument.
The general required information for the tested DTS instrument and the associated test setup
shall be recorded along with the calculated measurement specifications.
5 Measurement procedures for performance parameters
5.1 Temperature measurement error
5.1.1 Test procedure and conditions
The following steps shall be performed:
1) Use a general test setup as shown in Clause 4.
2) Make the total fibre length Z equal to or greater than the distance measurement range
quoted for the specific DTS instrument to be tested.
3) Place the DTS instrument in a thermal chamber and stabilize it at operating temperature (e.
g. 20 °C ± 0,5 °C). Give the instrument sufficient time before performing the following steps
to reach thermal equilibrium with the environment in accordance with the manufacturer's
recommendations (start-up time). The operating temperature shall be defined by the
manufacturer of the DTS instrument.
4) Calibrate the DTS instrument according to manufacturer's recommendations over a defined
fibre temperature range that corresponds to the application. The fibre temperature range
shall be agreed by the manufacturer and the customer.
5) Stabilize the temperature within ± 0,5 °C of controlled fibre length(s) D at three
representative temperatures T , T , T within the specified temperature range. The three
1 2 3
representative temperatures shall be agreed by the manufacturer and the customer.
6) Collect 20 temperature traces at each of the three required measurement times (shortest
time provided by the DTS instrument, recommended time, and longest possible provided by
the DTS instrument) for each fibre temperature.
NOTE The same data sets can be used for the performance evaluation of spatial resolution, spatial
temperature uncertainty, and temperature repeatability.
5.1.2 Parameter calculation
For calculation of the temperature measurement error, the following steps shall be performed
(see Figures 4 through 5):
1) Compute the average of all 20 temperature traces for each temperature sample point over
the entire location.
2) Calculate the smoothed average by computing a centred and uniformly weighted moving
average over 51 of the averaged temperature data (DTS readings).
3) Compute the average error for each sample point by subtracting the smoothed average from
the actual fibre temperature (as measured by an independent calibrated reference sensor)
over the entire location. See Figure 5.
4) Calculate the absolute average error by taking the absolute value of each average error for
each temperature sample point.
5) The temperature measurement error for that set of test conditions is the maximum value of
all absolute average error values that correspond to measurements collected from the fibre

length that was clearly inside the stabilized thermal chamber. Temperature data of fibre
lengths outside the stabilized thermal chamber (e. g. end or lead in fibre lengths, W length
of fibre) shall not be used for computation of the temperature measurement error. See
Figure 6.
6) Repeat calculation steps 1 through 5 for all other sets of test conditions (a total of 3
conditions exist for each measurement time).
7) Record the test parameters and all 9 measured values for the temperature measurement
error.
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Figure 4 – Temperature measurement error calculation: step 1
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Figure 5 – Temperature measurement error calculation: steps 2 through 3

– 16 – IEC 61757-2-2:2016 © IEC 2016
IEC
Figure 6 – Temperature measurement error calculation: steps 4 through 5
5.2 Spatial resolution
5.2.1 Test procedure and conditions
The following steps shall be performed:
1) Give equipment sufficient time before the test to reach thermal equilibrium with the
environment in accordance with the manufacturer's recommendations.
2) Use a general test setup as shown in Clause 4.
3) The hot spot fibre segment lengths shall be equal to the following:
a) The A length shall be less than the claimed DTS instrument spatial resolution, such
that no single temperature point will show the hot spot reference temperature.
b) The B length shall be equal to the claimed spatial resolution for the DTS instrument
being tested, such that one data point shows a temperature value increase > 90 % of
the segment reference temperature.
c) The C length shall be greater than 4 times the claimed spatial resolution for the DTS
instrument being tested.
4) The sample spacing shall be less than or equal to one-half the claimed spatial resolution.
5) Hot spots shall be generated according to 3.6.
6) Collect performance data set as specified in 5.1 using a measuring time which corresponds
to the needs of the application (e. g. 10 min).
5.2.2 Parameter calculation
For calculation of the spatial resolution (Figure 7) the following steps shall be performed:
1) Spatial resolution is equal to the B fibre segment length, and is validated with this test by at
least one data point in the B segment fibre calculating a temperature > 90 % of the hot spot
reference temperature increase above the surrounding fibre temperature.

2) The A fibre segment shall validate that no data points show the hot spot reference
temperature.
3) Afterwards, the spatial resolution length, the C fibre hot spot segment, shall show all data
points equal to the hot spot reference temperature within the expected spatial temperature
uncertainty.
4) Record the B fibre segment length as spatial resolution.
Fiber coil Fiber coil Fiber coil
Length=A Length=B Length=C
100 %
Length B
90 %
DTS indication
Reference
temperature
1 m 1,5 m 6 m
2 000 2 005 2 010 2 015 2 020 2 025 2 030
Location (m)
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Figure 7 – Spatial resolution illustration
5.3 Temperature repeatability
5.3.1 Test procedure and conditions
The following steps shall be performed:
1) Give equipment sufficient time before the test to reach thermal equilibrium with the
environment in accordance with the manufacturer's recommendations.
2) Use a general test setup as shown in Clause 4.
3) Collect performance data set as specified in 5.1.
4) Collect 20 consecutive traces with a quoted spatial resolution over the total fibre length Z
after the fibre temperature is stabilized:
a) for each measurement time (shortest time provided by the DTS instrument,
recommended time, and longest possible provided by the DTS instrument); and
b) for three representative fibre temperatures (T , T , T ) according to the desired
1 2 3
application.
5) The performance data set comprises 9 data subsets for above specified pairs of
measurement time and fibre temperature.
6) Each subset is used to evaluate the values of temperature repeatability over length.
5.3.2 Parameter calculation
For calculation of the temperature repeatability (Figure 8) the following steps shall be
performed:
1) Collect 20 consecutive traces for each data subset (e. g. traces for 10 min measurement
time at one representative fibre temperature (T , T , T ) as shown in Figure 4).
1 2 3
2) Calculate twice the standard deviation of temperature for each sample point over time
(20 consecutive traces). Plot above calculated values versus distance.
Temperature (°C)
∆ 20 °C
– 18 – IEC 61757-2-2:2016 © IEC 2016
3) Create a 51-point centred and uniformly weighted moving average curve S to use to select
i
the reported distance based temperature repeatability values for each measurement time
at each fibre temperature.
4) Report the maximum temperature repeatability value of the data set created in step 3.
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Figure 8 – Temperature repeatability calculated from Figure 4
5) Repeat this procedure at each measurement time for the remaining two representative fibre
temperatures (T , T , T ).
1 2 3
5.3.3 Formulas
Standard deviation in 5.3.2, step 2 is calculated by:
N N
 
1 1
 
S (i)= T (i)− T (i) (1)
x j j
∑ ∑
 
N−1 N
 
j=1 j=1
 
where
th th
T (i) is the collected temperature data at i location of j trace;
j
th
S (i) is the standard deviation for each data point (i location within a trace) over time (N
x
consecutive traces);
N is the number of traces (N = 20).
The temperature repeatability S using the moving average applied on twice the standard
...