What are the benefits of using infrared line scanners for high resolution thermal imaging applications?

Both infrared line scanners and thermal imagers are increasingly used in industrial thermal imaging applications, however for certain applications the infrared line scanners are preferable.

Firstly, we will consider more about infrared linescanners and thermal imagers.

Infrared Linescanners

The standard operating mode of an infrared linescanner uses the periodic deflection of the optical beam path of just one very fast and highly accurate point detector in the form of a scan line. Within the scan angle of 80° (+/- 40°), a closed line is created to record the temperature profile of a measuring object.
For moving targets, such as when rolling steel, this results in a high-resolution thermogram (surface temperature measurement).

The models of the AMETEK Land LSP-HD linescanner series capture the temperatures of 1,000 overlapping measuring points per scan with a fully digital scan at a frequency of up to 150 Hz. The scan line can be subdivided into individual zones and these zone values can be used to control and document thermal processes.
The main advantage of the LSP-HD linescanner is that every single point of the measuring line is recorded by the same cooled infrared detector to provide the highest possible homogeneity measurement. The homogeneity within the scans then depends mainly on the reproducibility (typ. <0.5 K).

Especially in applications in which the relative temperature distribution of the measurement object has only very small tolerances, e. g. to reduce internal stress or thickness variations, it is of fundamental importance to ensure a highly homogeneous temperature profile detection in these processes. 

Thermal Imagers 
Industrial thermal imagers and systems cover various temperature ranges and optimised spectral ranges to suit specific applications.

The functional principle of these thermographic cameras is similar to visual cameras (e.g. CCD/CMOS cameras) based on the respective integrated detector which is designed as a so-called FPA detector (Focal Plane Array). Although current smartphone models have cameras with 12 million or even more pixels, the number of pixels of the infrared detectors - depending on the type of detector - is limited.

To provide a radiometric (traceable to National Standards such as UKAS) thermography camera, a suitable signal strength is required for every single pixel. Due to this, current infrared detectors have relatively low pixel resolutions of 384x288 or 640x480 pixels with 1,024x768 used in some extreme cases.

The individual pixels in such FPA detectors are not 100% equal, this means that the generated electrical signal, which is translated to measured temperature, can also vary when measuring an absolutely temperature-homogenic surface. For example, with a 640x480 pixel detector, there are more than different 300.000 pixels.

For AMETEK Land thermal imagers, we carry out an advanced full-radiometric calibration of the entire detector, calibrating every single pixel to provide accurate and traceable results. During this calibration images are recorded and displayed in an extended calibration protocol in order to document the homogeneity of the thermographic image.

It should be noted that the signal of individual camera pixels of a thermographic camera relative to each other - within the camera calibration - may differ within the camera specifications.

Since virtually every pixel represents a "separate detector", a measurement accuracy of the thermographic camera can in in rare worst-cases lead to a deviation in the amount of twice the measurement accuracy. For example, with +/- 2% measurement inaccuracy, pixel would have 1 -2% and pixel 2 +% inaccuracy.

So why use AMETEK Land infrared linescanners for high resolution thermal imaging applications?
For processes requiring non-contact temperature measurement in which a very high homogeneity of the measurement over the measuring line / area is required, an AMETEK Land LSP-HD linescanner is preferable in performance to even a radiometrically verified thermographic camera.

For example, in float glass applications in the Lehr zone, it is critical to get an extremely high homogeneity across the flat glass running through the Lehr zone in order to prevent any mechanical stress, which will lead to cracks and possibly a complete break of the flat glass.

Cracks in float glass applications due to slight temperature differences and mechanical stress
Cracks in float glass applications due to slight temperature differences and mechanical stress

When used in conjunction with suitable encoders LSP-HD linescanners can generate thermograms for dynamic processes, such as coiling and rolling, to give input into automated control systems and help optimise industrial thermal processes.

High resolution thermal images, created with 1.000 points per line infrared line scanner in moving steel strip
High resolution thermal images, created with 1.000 points per line infrared line scanner in moving steel strip

What are the benefits of Infrared Linescanners?

For high speed and high homogeneous thermal imaging applications the LSP-HD linescanners are recommended to measure and analyse “real temperature differences” of the moving object in float glass, metal strip applications and many more.

Benefits include:

  • High pixel resolution of 1.000 per line.
  • Complete coverage of the measure surface with overlapping pixels.
  • Up to 150 Hz (lines per second) – creates a high homogeneous thermal image.
  • With the one detector scanner technology, the repeatability of temperature reading of each pixel is <0,5K – the differences measured are real temperature differences.

Infrared line scanners should be used in fast thermal imaging applications where a most accurate and homogeneous temperature reading is required.

 

 

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