This Article is about:
- Temperature Range explained
- Sub-ranges of a thermal camera
- Automatic and manual range selection
Temperature Range explained
The Temperature Range indicates the range of temperatures a thermal imager can measure and show as different colors on its display.
If the camera is aimed at an object that has a temperature just higher, than the maximum of the thermal imager range, like hot red glowing metal for example, while the camera has the measurement range of up to 150 °C, the camera will in most of cases just show a saturated display and take no damage.
If the amount of radiation coming from the hot source within the camera field of view becomes dangerous to the IR detector, a shutter may automatically operate to close the detector to protect it against excessive radiation. In this case the camera may need to be restarted.
At the same time, if you point your thermal imager at a very hot object, like the sun, molten steel or electric welding arc, the amount of infrared radiation coming from such hot objects may actually damage the infrared sensor of the camera and therefore such situations should be avoided.
A good rule of thumb in this case may be not to use the thermal camera on the objects having the temperatures more than 100° C higher, than the maximum temperature measured by the thermal camera or the thermal camera subrange currently in use.
Sub-ranges of the thermal camera
Sensors used in thermal cameras have limited dynamic range, i.e. the difference between maximum and minimum signal it can provide, or the difference between maximum and minimum amount of radiation it can measure and convert into temperature readings. Consequently the simple cameras don't cover a very broad temperature range and use only one subrange, equal to the whole measurement range of the camera. This is usually either -20...+80 °C, -20...+100 °C or -20...+150 °C, depending on the camera model.
The cameras, which cover wider temperature range usually have the measurement range split in subranges, to cover the whole measurement range of the camera. For example, Ti300+, Ti401Pro and TiX501 cover their measurement range with subranges of -20...+100 °C and -20...+650 °C. Ti480Pro and TiX580 cover their measurement range with subranges of -20...+100 °C and -20...+1000 °C. TiS55+ and TiS75+ cover their measurement range with subranges of -20...+150°C and -20...+550 °C. RSE300 and RSE600 cover their measurement range with subranges of -20...+100° C and -20...+1200°C.
When the camera measurement range is extended, the measurement sensitivity decreases, or the value of the NETD, a parameter describing the minimum temperature difference, which the thermal camera can show against noise, becomes bigger. The maximum sensitivity of the camera is usually achieved when the lowest available measurement range is being used.
| An image from a thermal camera with the range -20...+80 °C selected | An image from a thermal camera with the range -20...+250 °C selected |
When the camera switches to higher temperature subranges, it delivers specified accuracy within the temperatures starting from the highest temperature of the previous, lower measurement subrange, and up to the maximum temperature of the subrange. In this way the thermal camera provides specified accuracy within the whole measurement range.
| An image from a thermal camera with the range -20...+80 °C selected and a hot object in the image |
An image from a thermal camera with the range -20...+1500 °C selected and a hot object in the image |
At the same time, due to the way, how the temperature measurement is organized and the difference in the results delivered by different subranges for different temperatures, it is always recommended to use the lowest possible range for the temperatures being measured. A good option may be relying on the automatic range selection provided by the camera, which selects the range providing the best accuracy and sensitivity for the temperatures in the scene.
Automatic and Manual range selection
The thermal cameras for basic applications usually have only one subrange covering the whole camera measurement range, or provide automatic range selection, so the user does not need to select measurement range manually to get the correct measurements. The camera will automatically detect the temperatures within the scene the camera sees and if necessary will automatically switch to the range which will provide the best sensitivity and measured temperature coverage.
For professional and expert use there is sometimes a need to use specific measurement range and ignore the temperatures, which are outside of this range. For those, who need to be able to select the range manually, the cameras like Ti300+, Ti401Pro, Ti480Pro, TiX501 and TiX580 provide both possibilities, to use automatic range selection, the default settings of the camera, or to select the measurement range manually via the camera menu.