How to choose an infrared thermal imaging camera

In recent years, infrared thermal imaging cameras have increasingly occupied an important position in steel, petrochemical, electric power, fire protection, automobile and other industries. Thermal imaging camera technology is developing rapidly around the world. The United States leads the world in infrared thermal imaging camera technology. At present, the world's top three infrared thermal imaging camera brands RNO, FLIR and FLUKE are all American companies.

1. Thermal imaging principle

Light is familiar visible light, which is an electromagnetic wave that can be felt by the human eye. The wavelength of visible light is: 0.38-0.78 microns. Electromagnetic waves shorter than 0.38 microns and electromagnetic waves longer than 0.78 microns cannot be felt by the human eye. Electromagnetic waves shorter than 0.38 microns are located outside the purple part of the visible light spectrum and are called ultraviolet rays. Electromagnetic waves longer than 0.78 microns are located outside the red part of the visible light spectrum and are called infrared rays. Infrared rays, also known as infrared radiation, refer to electromagnetic waves with a wavelength of 0.78~1000 microns. The part with a wavelength of 0.78 to 2.0 microns is called near infrared, and the part with a wavelength of 2.0 to 1000 microns is called thermal infrared. A camera produces a photo through imaging, and a TV camera produces a television image through imaging, both of which are visible light imaging. In nature, all objects can radiate infrared rays, so a detector is used to measure the infrared ray difference between the target itself and the background and obtain different infrared images. The image formed by thermal infrared rays is called a heat map. The thermal image of the target is different from the visible light image of the target. It is not a visible light image of the target that can be seen by the human eye, but an image of the target surface temperature distribution. In other words, infrared thermal imaging prevents the human eye from directly seeing the surface temperature of the target. The distribution becomes a thermal image that can be seen by the human eye representing the temperature distribution of the target surface.

Infrared thermal imaging cameras have two different principles: photon detection and thermal detection. The former mainly uses the electrical effect generated by photons on semiconductor materials for imaging, and has high sensitivity. However, the temperature of the detector itself will affect it, so it needs to be cooled down. The latter converts heat caused by light into electrical signals, is less sensitive than the former and does not require cooling. In addition, the thermal imager is also classified according to its working band and the photosensitive material used. Common thermal imagers work at 3 to 5 microns or 8 to 12 microns. Commonly used photosensitive materials include lead sulfide, lead selenide, indium telluride, lead tin telluride, mercury cadmium telluride, doped germanium and doped silicon. Depending on the number of photosensitive elements and the mode of movement, there are mechanical scanning, gaze imaging types, etc.

2. Thermal imaging application

Advanced equipment detection methods such as infrared detectors play an important role. First, successful fault diagnosis, especially one that reports faults appropriately in advance, will yield significant benefits. This benefit is extremely considerable in special circumstances; secondly, fault diagnosis technology can play a huge auxiliary role in equipment maintenance. It can not only greatly save human resources, but also change the maintenance method - gradually replace the planned maintenance method with advanced state maintenance method, and even have a positive impact on the management method of inventory spare parts.

3. Thermal imaging camera parameters

How to choose an infrared thermal imaging camera

(1) Detector resolution of infrared thermal imaging camera

The current mainstream detector resolution of infrared thermal imaging cameras is 160x120 (192,000 pixels), and the mainstream models basically have this pixel. There are also lower resolutions such as 60x60 (36,000 pixels), 80x60 (48,000 pixels), and 100x100 (100,000 pixels). There are also 384X288 (1.1 million pixels) and 640x480 (3 million pixels).

For handheld infrared thermal imaging cameras, 160x120 is the most golden resolution and has a very good price/performance ratio. For example, the resolution of the latest global best-selling RNO IR-160P is 160x120. Infrared thermal imaging cameras with a resolution lower than this cannot be used in many situations because the resolution is too low. The price of infrared thermal imaging cameras with more than 1 million pixels has increased significantly, unless you have very high resolution requirements. Infrared thermal imaging cameras with over 1 million pixels are available.

(2) Lens focal length of infrared thermal imaging camera

The lenses of general infrared thermal imaging cameras can be replaced. However, the standard equipment provided by the manufacturer is generally one lens. Basically all manufacturers provide a lens of about 20MM as standard. A lens of this focal length basically takes into account two aspects: field of view size and magnification ratio. Generally, customers can use standard lenses.

Optional options include a 115MM telephoto lens or a 10-15MM wide-angle lens. A telephoto lens will improve long-distance recognition, but will greatly reduce the field of view. On the contrary, short-focus lenses greatly increase the field of view, but will reduce the recognition rate.

The image spacing, spatial resolution, field of view, and identification distance are determined by the detector resolution and lens focal length. Many brands are promoting these four indicators. In fact, if the detector resolution and lens focal length of the infrared thermal imaging camera are fixed, these four indicators are fixed, and these four indicators are calculated. So you don’t need to pay too much attention when purchasing.

(3) Frame rate of infrared thermal imaging camera

Frame rate is the second most important indicator when purchasing an infrared thermal imaging camera. The frame rate refers to the number of images that the thermal imaging camera can capture, process, and display within 1 second. The faster the sensor responds and the higher the internal circuit processing rate, the higher the achievable frame rate. Thermal imaging cameras with high frame rates are suitable for capturing the temperature movement of high-speed objects and objects with high-speed temperature changes.

(4)Temperature measurement range

This is the third most important indicator of an infrared thermal imaging camera. Each model of thermal imaging camera has its own specific temperature measurement range. Therefore, the user's measured temperature range must be considered accurately and comprehensively, neither too narrow nor too wide. According to the blackbody radiation law, the change in radiant energy caused by temperature in the short-wavelength band of the spectrum will exceed the change in radiated energy caused by the emissivity error. Therefore, users only need to purchase an infrared thermal imaging camera within the temperature range they measure.

(5)Temperature measurement accuracy

Generally, the temperature measurement accuracy of infrared thermal imaging cameras is: accuracy ±2°C and ±2% of possible readings. So basically there is nothing to choose from.

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