GB/T 38238-2019 English PDF (GBT38238-2019)

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GB/T 38238-2019: Non-destructive testing instruments -- Infrared thermography -- System and equipment -- Description of characteristics
GB/T 38238-2019
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 19.100
J 04
Non-destructive testing instruments - Infrared
thermography - System and equipment - Description
of characteristics
ISSUED ON: OCTOBER 18, 2019
IMPLEMENTED ON: MAY 01, 2020
Issued by: State Administration of Market Regulation;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 System overview ... 4
5 Objective lens ... 5
6 Detector ... 6
7 Image processor ... 8
8 Excitation source ... 10
9 Integrated performance parameters and functions of infrared systems and
equipment ... 12
10 Auxiliary equipment ... 14
Non-destructive testing instruments - Infrared
thermography - System and equipment - Description
of characteristics
1 Scope
This Standard specifies the functions and performance parameters of infrared
thermal imaging systems, equipment and accessories for non-destructive
testing.
This Standard applies to focal plane infrared thermal imagers. Optical scanning
infrared thermal imagers may refer to this Standard.
2 Normative references
The following referenced documents are indispensable for the application 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.
GB/T 12604.9 Non-destructive testing - Terminology - Terms used in infrared
testing
GB/T 19870 Industrial inspecting thermal imagers
3 Terms and definitions
For the purpose of this document, the terms and definitions defined in GB/T
12604.9 and GB/T 19870 apply.
4 System overview
Figure 1 is the block diagram of an infrared thermal imaging system, including
an objective lens, a detector, an image processor, a display, an excitation
source, auxiliary equipment, etc. The objective lens images the infrared
radiation of the object to be tested on the detector array, and the detector
converts it into an electrical signal, and then the image processor further
processes it to obtain information about the object to be tested.
affects the temperature measurement sensitivity of the testing system. The
larger the aperture (the smaller the f number), the more the amount of light
entering, the higher the system’s temperature measurement sensitivity, the
smaller the temperature measurement range; the smaller the aperture (the
larger the f number), the less the amount of light entering, the lower the
system’s temperature measurement sensitivity, the larger he temperature
measurement range.
The aperture of the lens needs to be larger than the size of the detector to
ensure that each element of the detector receives infrared radiation.
6 Detector
6.1 General
Infrared thermal imaging systems use detectors to convert radiant energy into
measurable electrical signals. Commonly used infrared radiation sensors
include: microbolometers, optoelectronics, pyroelectric or quantum sensors,
etc. The detector performance directly affects the spatial, temporal, and
temperature resolution of the testing system.
6.2 Detector type
Infrared thermal imaging detectors mainly have two types, i.e. thermal sensors
and quantum sensors. Thermal sensors operate at room temperature, such as
microbolometers and photoelectric sensors. Quantum sensors need to be
cooled to a lower operating temperature. Compared to thermal sensors,
quantum sensors have higher sensitivity and sampling frequency.
6.3 Detector array
Infrared detectors can be single point, line array or two-dimensional array. A
single point detector requires a scanning system to measure the object to be
tested point by point and form a thermal image. A line array detector can be
used to image moving objects such as production lines. A two-dimensional
array detector uses a sensor unit to perform point-by-point scanning to obtain
information to form a thermal image.
6.4 Scanning system
Mechanical scanning can be achieved by moving mirrors, prisms, etc. However,
since mechanical scanning limits the frame rate, thermal imagers with
mechanical scanning system are not suitable for capturing high speed images
compared to infrared thermal imagers with two-dimensional array detector.
6.5 Working band
range.
6.12 Start-up time
For uncooled detectors, a certain amount of preheating is required at startup to
ensure that the temperature of the equipment itself is stable, reducing the effect
of temperature drift on the measurement. For refrigerating detectors, it takes a
certain amount of time to start up to ensure that the detector reaches the
required operating temperature. The starting time is mainly determined by the
type of chiller and the mode of cooling.
7 Image processor
7.1 General
The image processor is used for the acquisition, analysis, processing, display
and storage of infrared thermography. The analysis and processing of infrared
thermography usually includes spatial distribution and changes with time of
temperature fields, image enhancement, noise reduction, etc. The performance
of the image processor mainly affects the speed, dynamic range, and imaging
effects of the testing system.
7.2 Image acquisition
7.2.1 Timed acquisition
Timing acquisition refers to image acquisition based on the internal clock of the
system. Timing acquisition includes: single frame acquisition, equal time
interval acquisition, and arbitrary set time interval acquisition.
7.2.2 Trigger acquisition
Trigger acquisition is image acquisition based on the trigger source signal. The
trigger source can be a trigger signal set internally by the system and a trigger
signal input externally. This function is commonly used in active infrared thermal
imaging testing methods, including pulsed thermal imaging, step thermal
imaging, phase-locked thermal imaging, and vibrational thermal imaging.
7.2.3 Last image hold
Last image hold is the function of holding the current view during the operation
of the infrared thermal imager.
7.3 Image display
Use the display to display the thermal image visible to human eyes, usually
7.5.6 Fusion of visible light and infrared images
The infrared thermal image and the visible light image collected at the same
viewing angle are subjected to adjustments of different weight ratios according
to different background settings, to achieve simultaneous display of the infrared
image and the visible light image on the same screen.
7.6 Image recording
Image recording shall have at least continuous recording and single frame
recording functions, and record instrument parameter settings and testing
conditions related to temperature calculation. Image recording should have full
dynamic range thermal image raw data recording function.
7.7 Image reading
Image reading is to comprehensively retrieve the stored image information, and
at the same time, it shall be able to display the instrument parameter settings
and testing conditions during the acquisition, so as to facilitate the analysis of
the testing results.
8 Excitation source
8.1 General
Active infrared thermal imaging methods require an external excitation source
to heat the material. The appropriate excitation source and modulation method
shall be selected according to the object to be tested and the purpose of testing.