kSIST FprEN 17501:2022

Non-destructive testing - Thermographic testing - Active thermography with laser excitation

This document determines the guidelines and the specifications for non-destructive testing using active thermography with laser excitation.
Active thermography with laser excitation is mainly applicable, but not limited to different materials (e.g. composites, metals, ceramics) and to:
-   the detection of surface-breaking discontinuities, particularly cracks;
-   the detection of discontinuities located just below the surface or below coatings with an efficiency that diminishes rapidly with a few mm depth;
-   the detection of disbonds and delamination parallel to the examined surface;
-   the measurement of thermal material properties, like thermal diffusivity;
-   the measurement of coating thickness.
The requirements for the equipment, for the verification of the system, for the surface condition of the part to be tested, for the scanning conditions, for the recording, the processing and the interpretation of the results are specified. Acceptance criteria are not defined.
Active thermography with laser excitation can be applied in industrial production as well as in maintenance and repair (vehicle parts, engine parts, power plant, aerospace, etc.).

Zerstörungsfreie Prüfung - Thermografische Prüfung - Aktive Thermografie mit Laser-Anregung

Dieses Dokument bestimmt die Leitlinien und Spezifikationen für zerstörungsfreie Prüfungen mittels aktiver Thermografie mit Laser Anregung.
Aktive Thermografie mit Laser Anregung ist hauptsächlich, aber nicht ausschließlich auf verschiedene Werkstoffe (z. B. Verbundstoffe, Metalle, Keramik) und bei Folgendem anwendbar:
   Erkennung von zur Oberfläche hin offenen Unregelmäßigkeiten, besonders von Rissen;
   Erkennung von Unregelmäßigkeiten unmittelbar unter der Oberfläche oder unter Beschichtungen mit einem Wirkungsgrad, der bereits in einer Tiefe von wenigen mm schnell abnimmt;
   Erkennung von Ablösungen und Schichtablösung parallel zur untersuchten Oberfläche;
   Messung von thermischen Werkstoffeigenschaften, wie z. B. der thermischen Diffusivität;
   Messung der Beschichtungsdicke.
Es werden die Anforderungen an die Geräte, die Verifizierung des Systems, die Oberflächenbeschaffenheit des zu prüfenden Teils, die Abtastbedingungen, die Aufzeichnung sowie an die Verarbeitung und Auswertung der Ergebnisse festgelegt. Annahmekriterien werden nicht festgelegt.
Aktive Thermografie mit Laser Anregung kann bei der industriellen Fertigung sowie bei der Wartung und Reparaturen (von Autoteilen, Motorteilen, Kraftwerken, in der Luft  und Raumfahrtindustrie usw.) angewendet werden.

Essais non destructifs - Analyse thermographique - Thermographie active avec excitation laser

Le présent document définit les lignes directrices et les spécifications applicables aux essais non destructifs par thermographie active avec excitation laser.
La thermographie active avec excitation laser est principalement utilisée pour différents matériaux (composites, métaux, céramiques par exemple) sans toutefois s’y limiter et pour :
   la détection des discontinuités débouchantes, notamment des fissures ;
   la détection des discontinuités situées juste en dessous de la surface ou sous des revêtements, avec une efficacité qui diminue rapidement sur une profondeur de quelques millimètres ;
   la détection des décollements et délaminations parallèles à la surface examinée ;
   le mesurage des propriétés thermiques des matériaux, telles que la diffusivité thermique ;
   le mesurage de l’épaisseur d’un revêtement.
Les exigences applicables à l’appareillage, à la vérification du système, à l’état de surface de la pièce à contrôler, aux conditions de balayage, à l’enregistrement, au traitement et à l’interprétation des résultats sont spécifiées. Les critères d’acceptation ne sont pas définis.
La thermographie active avec excitation laser peut être utilisée pour la production industrielle, ainsi que pour la maintenance et la réparation (pièces de véhicule, pièces de moteur, centrales électriques, aérospatiales, etc.).

Neporušitvene preiskave - Termografsko preskušanje - Aktivna termografija z laserskim vzbujanjem

General Information

• Status: Not Published
• Public Enquiry End Date: 23-Jul-2020
• ICS: 19.100 - Non-destructive testing
• Technical Committee: PKG - Testing of metallic materials
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 15-Jun-2022
• Due Date: 20-Aug-2022
• Ref Project: EN 17501:2022 - Non-destructive testing - Thermographic testing - Active thermography with laser excitation

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 17501:2020
01-julij-2020
Neporušitvene preiskave - Termografsko preskušanje - Aktivna termografija z
laserskim vzbujanjem
Non-destructive testing - Thermographic testing - Active thermography with laser
excitation

Zerstörungsfreie Prüfung - Thermografische Prüfung - Aktive Thermografie mit Laser-

Anregung
Essais non destructifs - Analyse thermographique - Thermographie active avec
excitation laser
Ta slovenski standard je istoveten z: prEN 17501
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
oSIST prEN 17501:2020 en,fr,de

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

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oSIST prEN 17501:2020
DRAFT
EUROPEAN STANDARD
prEN 17501
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2020
ICS 19.100
English Version
Non-destructive testing - Thermographic testing - Active
thermography with laser excitation

Essais non destructifs - Analyse thermographique - Zerstörungsfreie Prüfung - Thermografische Prüfung -

Thermographie active avec excitation laser Aktive Thermografie mit Laser-Anregung

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

CEN/TC 138.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations

which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC

Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.

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

aware and to provide supporting documentation.

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

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

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17501:2020 E

worldwide for CEN national Members.
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Contents Page

European foreword ....................................................................................................................................................... 3

1 Scope .................................................................................................................................................................... 4

2 Normative references .................................................................................................................................... 4

3 Terms and definitions ................................................................................................................................... 5

4 Qualification and certification of personnel ......................................................................................... 5

5 Principle of laser thermography and instrumental setup ............................................................... 6

5.1 General ................................................................................................................................................................ 6

5.2 Typical configurations of excitation ......................................................................................................... 7

5.3 Laser and laser optics requirements ....................................................................................................... 8

5.4 Scanning system requirement ................................................................................................................. 10

5.5 Specifications of the IR camera ............................................................................................................... 12

5.6 Data processing and analysis techniques ............................................................................................ 13

5.7 Data processing for crack characterization........................................................................................ 16

5.8 Data processing and analysis techniques for the determination of lateral thermal

diffusivity ........................................................................................................................................................ 19

5.9 Data processing and analysis techniques for emissivity correction ......................................... 19

5.10 Data processing and analysis techniques for coating thickness control ................................. 19

6 Reference test specimens .......................................................................................................................... 19

7 Calibration, validation and performance of testing ........................................................................ 19

8 Evaluation, classification and registration of thermographic indications .............................. 20

9 Reporting ........................................................................................................................................................ 20

Annex A (informative) List of influential parameters for the NDT qualification of laser

thermographic system ............................................................................................................................... 22

Annex B (informative) Reference blocks ............................................................................................................ 26

Bibliography ................................................................................................................................................................. 31

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European foreword

This document (prEN 17501:2020) has been prepared by Technical Committee CEN/TC 138 “Non-

destructive testing”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
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1 Scope

This document determines the guidelines and the specifications for non-destructive testing using active

thermography with laser excitation.

Active thermography with laser excitation is mainly applicable, but not limited to different materials

(e.g. composites, metals, ceramics) and to:
— the detection of surface-breaking discontinuities, particularly cracks;

— the detection of discontinuities located just below the surface or below coatings with an efficiency

that diminishes rapidly with a few mm depth;
— the detection of disbonds and delamination parallel to the examined surface;
— the measurement of thermal material properties, like thermal diffusivity;
— the measurement of coating thickness.

The requirements for the equipment, for the verification of the system, for the surface condition of the

part to be tested, for the scanning conditions, for the recording, the processing and the interpretation of

the results are specified. Acceptance criteria are not defined.

Active thermography with laser excitation can be applied in industrial production as well as in

maintenance and repair (vehicle parts, engine parts, power plant, aerospace, etc.).

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

EN 16714-1, Non-destructive testing — Thermographic testing — Part 1: General principles

EN 16714-2, Non-destructive testing — Thermographic testing — Part 2: Equipment

EN 16714-3, Non-destructive testing — Thermographic testing — Part 3: Terms and definitions

EN 17119, Non-destructive testing — Thermographic testing — Active thermography

EN ISO 9934-2, Non-destructive testing — Magnetic particle testing — Part 2: Detection media

(ISO 9934-2)

EN 12464-1, Light and lighting — Lighting of work places — Part 1: Indoor work places

CEN/TR 14748, Non-destructive testing — Methodology for qualification of non-destructive tests

DIN 54184, Non-destructive testing — Pulse thermography using optical excitation
VDI/VDE 5585-1, Technical temperature measurement — Temperature measurement with
thermographic cameras — Metrological characterization
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3 Terms and definitions

For the purposes of this document, the terms and definitions given in EN 16714-3 and EN 17119 and

the following apply.

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

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
laser

light amplification by stimulated emission of radiation used as light source for thermal excitation in

laser thermography
3.2
scanning system

system which provides relative movement of the shaped laser beam, the surface of the test object

and/or the IR camera
3.3
flying spot technique
scanning of the shaped laser beam on the surface of the test object
3.4
spot diameter

full width at half maximum of the irradiation profile of the laser beam at the target plane

3.5
scanning speed
relative velocity of the laser spot at the target plane
3.6
illumination pattern
spatial distribution of the laser irradiation at the target plane
4 Qualification and certification of personnel

The competence of the test personnel using this document shall be demonstrated according to

EN ISO 9712 or an equivalent formalized system and the following:

— the relevant standards, rules, specifications, test instructions and description of the methods;

— the type of equipment and its operation;
— the mounting, design, structure and operation of the objects under test;

The test personnel shall have sufficient knowledge about the test object and about the possible

diagnostic findings.
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5 Principle of laser thermography and instrumental setup
5.1 General

Laser thermography is a technique of active thermography. A very basic experimental setup is given in

Figure 1. The absorption of laser radiation at the surface generates the heat flux into the test object

(also called photothermal effect). The illumination pattern of the laser can be designed to deliver a

focused spot, a line, or an area (e.g. square or circle). The presence of a discontinuity inside or on the

surface of the test object alters the heat flux in a specific way. As a result, the shape and symmetry of the

induced heat flux pattern allows the testing to be optimized to different classes of discontinuities, like,

e.g. planar and volume defects or linear cracks or measurement of material properties that influence the

diffusion of heat. The resulting temporal evolution of the thermal radiation distribution on the surface

during or after laser illumination is acquired by an infrared (IR) camera, and converted to a signal that

can be analysed by different signal processing algorithms. One advantage of applying a laser as thermal

energy source is that a large spatial distance between source and test object surface can be achieved (of

typically some centimetres up to several metres). A further advantage when utilizing a laser is given by

its narrow emission spectrum, which can be clearly separated from the IR camera detection range. This

characteristic facilitates the reflection configuration without using additional filters.

Typically, high-power lasers with an output power of several watts to kilowatts are used. Due to

focusing to, e.g. a spot or a line, a high irradiance (MW to GW per m ) can be achieved. In order to test

the entire test object surface, the illumination needs to be scanned over the test object surface by a

relative movement between test object, laser, and/or IR camera.
NOTE As laser sources, continuous as well as pulsed laser systems can be used.

Since lasers typically allow very high modulation rates (kHz-range is easily achievable), different

temporal excitation and testing modes can be implemented.

The quality of the thermographic signal depends on a number of experimental setup and test object

parameters. In the following a list of preferable prerequisites to improve signal quality (i.e. signal to

noise ratio and contrast to noise ratio of detected discontinuity) is given:
— high laser power and/or irradiance;

— high and spatially homogenous spectral absorptance of the test object at the laser wavelength;

— high and spatially homogenous spectral emissivity of the test object at the IR camera wavelength;

— high temporal and mechanical stability between the devices moving relatively, i.e. the laser, the

scanning system and the IR camera;
— high responsivity and low NETD of the IR camera.

If, for instance, the absorptance or emissivity of the test object surface is not spatially homogenous, this

leads to in homogeneously distributed thermal radiation which can be misinterpreted as a defect

indication. In this case an additional coating of the surface might be applied.
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Key
1 Scanning system 5 Laser beam
2 Test object 6 IR camera
3 Discontinuity 7 Thermal radiation
4 Laser
Figure 1 — Schematic of laser thermography with movement of the test object
5.2 Typical configurations of excitation
5.2.1 General

According to EN 17119, laser thermography can be performed in static as well as in dynamic

configuration and with different types of temporal and spatial excitation.
5.2.2 Laser thermography in static configuration (without relative movement)

Laser thermography can be realized without any relative movement between illumination, test object

and IR camera. In this case, one or many thermogram(s) of the whole scene are acquired at the time(s)

of interest. The thermogram or thermogram sequence acquired can then be processed to indicate if any

discontinuity is present in the test object. In particular, pulse and lock-in thermographic testing

techniques that do not rely on a relative movement and that apply either a very short optical impulse or

a periodic optical excitation can be implemented using a laser as optical energy source.

5.2.3 Laser thermography in dynamic configuration (with relative movement)

Laser thermography can be realized with relative movement between illumination, test object and IR

camera. In this case, the IR camera is set to view either the area where the illumination is present, or an

area where the illumination is no longer present but where its thermal impact is still visible (time-lag).

The thermogram or thermogram sequence acquired can then be processed to indicate if any

discontinuity is present in the test object.
5.2.4 Laser thermography with different temporal excitations

Depending on the specific laser used, different temporal excitation modes can be implemented. In

particular, if a very short laser impulse is used, this resembles the pulse thermographic testing

technique using optical sources. Another known temporal technique is lock-in thermographic testing

using an optical source whose irradiance is periodically modulated, e.g. by a sine, a triangle or a

rectangular function. Laser sources allow for continuous wave (cw) operation and can be modulated up

to very high modulation rates (>10 kHz-range). Hence lasers can be applied for all known temporal

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excitation techniques and can, in addition to that, be used up to very high modulation frequencies as

well as for arbitrary temporal excitation functions.
5.2.5 Laser thermography with different spatial excitations

Depending on the specific laser used, different spatial excitation modes can be implemented. A focused

laser spot can be used e.g. for the flying spot technique, where the test object is continuously or

randomly scanned with a laser spot. In this case 3D heat transfer shall be considered. A focused laser

line can be used for techniques where the test object is continuously or randomly scanned with a laser

line. In this case only 2D heat transfer shall be taken into account. A widened laser beam can be used to

illuminate a larger area homogeneously. Depending on the size of this area, only 1D heat transfer in

depth direction shall be considered.

Illumination patterns like spots or lines cannot only be used to locate and quantify discontinuities, but

can also be exploited to determine the directional dependence on thermal material properties, e.g. the

thermal diffusivity.
5.3 Laser and laser optics requirements
5.3.1 Laser irradiance and wavelength

The laser system used for inspection shall meet the specific requirements of the thermographic testing

task. For a specified IR camera the main parameters determining the minimum detectable temperature

increase on the test object surface by the IR camera are the irradiance of the laser radiation and the

optical and thermal material properties of the test object. Concerning the irradiance of the laser

radiation, the relationship with the temperature increase is linear. This means that the choices of laser

output power and focusing optics directly influence the achievable temperature increase. In addition,

the spectral absorptance of the test object at the laser wavelength determines how much of the incident

radiant energy is converted into heat. Therefore, if the absorptance is small, as it is for instance for

polished metals or partially transparent polymers, the laser irradiance shall be accordingly high. In the

best case, the laser wavelength is chosen to be at maximum of the spectral absorptance of the test

object. Additionally, the laser wavelength should be outside the spectral sensitivity range of the IR

camera to avoid damaging the detector and to avoid that the partially reflected laser radiation from the

test object can be confused with the thermal radiation from the test object. Besides the irradiance and

test object absorptance, the thermal material properties of the test object (i.e. thermal conductivity k,

specific heat c , and density ρ) determine the gained temperature increase due to laser heating. For the

two limiting cases of pulse and lock-in thermography, the temperature rise ΔT is proportional to

-1/2

(k*c *ρ) . This means that for highly thermally conducting materials only a small temperature rise is

generated. Accordingly, the laser irradiance shall be chosen high enough in order to compensate for a

sufficient temperature rise during testing.

NOTE For maximum laser power it should be considered that the test object is not destructed by e.g. melting,

oxidation, illumination induced colour changes or ageing of polymers. These effects are influenced not only by the

laser irradiance, but also by pulse length, thermal and optical material properties, chemical composition etc.

5.3.2 Spatial illumination shapes
5.3.2.1 General

The illumination pattern shall be chosen accordingly to the specific spatial and temporal excitation

mode used for testing. This can be performed by optical beam shaping devices.

Generally, fibre, solid state and gas lasers have a higher beam quality than diode lasers and can be

focused to a smaller width. For focused laser spots, the spot size is only given within the depth of field of

the laser optics.
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If the laser radiation is brought to the system by an optical fibre, this fibre and any additional optics

should be set so that the laser beam has a shape compatible with the inspection.
5.3.2.2 Spot

A round-shaped focused or collimated laser spot can be generated by an optical lens or mirror system.

In dependence on the type of laser and the optics used, different spot sizes can be obtained.

5.3.2.3 Straight line

A straight line-shaped focused laser can be generated by a cylinder lens or lens system. In dependence

on the type of laser and optics used, different line lengths, widths and shapes can be obtained. In this

case, the sensitivity of the detection is better for discontinuities whose orientation is parallel to the

laser line.
5.3.2.4 Area

A homogeneous illumination of a larger area is obtained by lens systems. If the laser source has to be

used for pulse or lock-in thermography, the dimension of the illuminated area shall be considerably

larger than the thermal diffusion length. Otherwise this configuration refers to the photothermal or

flying spot technique. A top-hat beam profile shall be chosen in favour of a Gaussian beam profile to

avoid lateral heat flows.
5.3.2.5 Pattern

Specific illumination patterns, deviating from the above mentioned shapes, can be generated by, e.g.

laser arrays, lens arrays or diffractive optical elements. The shape of the patterns can be optimized to

certain types of discontinuities.
5.3.3 Switchable laser for lock-in thermography and other temporal techniques

In all temporal excitation techniques, and especially in those which correlate the temporal excitation

function with the temporal temperature response of the test object, the irradiance of the laser shall be

controlled as exactly as possible. A common approach is to control the output power of the laser system

by an external function generator via an analogue voltage input, which can be triggered by the IR

camera. For best performance, the output power should have a linear relationship with the controlling

voltage such that the signal processing algorithm can be applied directly. If there is no linear

relationship, the characteristic curve of the laser (i.e. output power vs. controlling voltage) shall be

taken into account properly by the user. Concerning the temporal behaviour, the laser switch on and

switch off times shall be taken into account for the maximum possible modulation frequency.

5.3.4 Safety

The most important European standards on laser safety, safety of optical radiation and protection

measures are listed in the following:
— EN 60825 Safety of laser products contains several relevant parts, e.g.:

— EN 60825-1 Safety of laser products — Part 1: Equipment classification and requirements

— EN 60825-4 Safety of laser products — Part 4: Laser guards

— EN ISO 11553 Safety of machinery — Laser processing machines contains several relevant parts,

e.g.:

— EN ISO 11553-1 Safety of machinery — Laser processing machines — Part 1: General safety

requirements
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— EN ISO 11553-2 Safety of machinery — Laser processing machines — Part 2: Safety

requirements for hand-held laser processing devices
Eye protection:

— EN 207 Personal eye-protection equipment — Filters and eye-protectors against laser radiation

(laser eye-protectors)

— EN 208 Personal eye-protection — Eye-protectors for adjustment work on lasers and laser systems

(laser adjustment eye-protectors)
— EN 12254 Screens for laser working places — Safety requirements and testing
— EN 62471 Photobiological safety of lamps and lamp systems

During testing, the workplace shall be illuminated adequately and appropriately according to

EN 12464-1. If necessary, protective measures related to the working safety regulations and regulations

for artificial optical radiation are expected to be considered.

During testing, it shall be ensured that there are no flammable materials in the vicinity of the equipment

and the investigated object.

Further on, there is a risk of burning on heated parts of the radiation sources, of the test object and of

further objects within the beam path.
5.4 Scanning system requirement
5.4.1 General

The scanning system should allow the laser to reach the whole area to be inspected from one or

multiple positions of the laser, the IR camera and/or the test object while keeping the laser beam and

the inspection IR camera in focus. The maximum scanning speed is linked to the laser power density

and IR camera frame rate.

According to the application, the movement of any part of the scanning system will be step-by-step or

continuous.
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5.4.2 Test object position and orientation
Key

1 Scanning system r Radial distance of the IR camera and the surface of the test object

2 Test object φ Azimuthal angle between the IR camera and the surface of the test object

3 Discontinuity θT Polar angle between the IR camera and the
surface of the test object

4 Laser φ Azimuthal angle between the laser beam and the surface of the test object

5 IR camera θ Polar angle between the laser beam and the surface of the test object

rL Radial distance of the laser beam output and the surface of the test object
Figure 2 — Example of a scanning configuration for laser thermography

The depth of field of the IR camera and, in case of a focused laser, of the laser restrict the test object

orientation relative to the IR camera and the laser. Furthermore, both the absorptance and the

emissivity of the test object in the spectral range of the laser and the IR camera, respectively, depend on

the incidence angle. If those quantities are changed between or during measurements, the heating of the

test object and the thermal radiation detected by the IR camera will change as well. Therefore, the

relative position and orientation of test object, laser, and IR camera need to be defined and documented

well. One possible configuration given in spherical coordinates is illustrated in Figure 2.

5.4.3 Movement of the test object

In this case, the measurement system comprising the laser and IR camera is fixed and the test object is

moved in front of it during the acquisition (see Figure 2).
5.4.4 Movement of the whole measurement system

In this case, the test object is fixed. The measurement system comprising the laser and IR cameras

moved in front of the test object during the acquisition.
5.4.5 Movement of the laser beam through optics

In this case, the test object and the IR camera are both fixed during the acquisition, and an optical setup,

such as mirrors, goniometers or laser scanning heads, is used to deflect the laser beam.

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5.4.6 Movement of the laser beam and IR camera through optics

In this case, the test object and the IR camera are both fixed during the acquisition, and an optical setup,

such as mirrors or goniometers, is used to deflect both the thermal radiation and the laser beam.

5.4.7 Setup stability

When an acquisition requires the analysis of a thermogram sequence, it is primordial that the pixel

correspondence between the different images in the sequence is realized properly. Hence, the setup

should have a stability against vibrations and thermal drift such that the uncertainty of the movement

of any part of the setup is smaller than the spatial resolution of the IR camera.

5.5 Specifications of the IR camera
Table 1 provides the minimum requirements of the features of the IR camera.
Table 1 — Minimum requirements of the features of the IR camera
Feature Minimum requirement

1 Spectral range (µm) According to EN 16714-2. In addition, the spectral range of the IR

camera shall not overlap with the wavelength of the laser.

2 Temperature range The IR camera should be able to detect all temperature variations of

(K, digital unit) the test object. A corresponding temperature range shall be set for

this purpose. For IR cameras without temperature calibration, a
corresponding display range is set, e.g. by selecting a suitable
integration time.

3 Thermal resolution The thermal resolution can be described by the noise equivalent

(K, digital unit) temperature difference NETD (according to EN 16714-2) or an
equivalent parameter. This parameter shall be sufficiently smaller
than the apparent temperature difference induced by the heat
source. Typically it should be at least 2 to 3 times less and in some
specific cases it could be even lower (e.g. lock-in thermography).

4 Thermal short-term The temperature drift during the acquisition shall be smaller than the

stability (K/s) NETD so that it does not impact the thermal resolution. A mea
...