At the selection of a thermal imaging camera there are several technical factors that affect your choice. For example, resolution. But why is resolution so important in thermography?
Thermal resolution consists of the number of pixels on the sensor. At a higher resolution, each image contains more information. This makes it more likely to obtain accurate measurements.
During these measurements, the camera averages multiple pixels to determine the temperature. For older systems this was 3×3 pixels, in modern devices we calculate better with 5×5 pixels.
The spatial resolution of a thermal imaging camera is based on the number of pixels and the image that reaches the sensor. Together, they determine how accurate the temperature measurements are.
There are three components that affect spatial resolution:
- Field of View (FOV).: the maximum area the sensor can "see. The FOV is determined by the distance and the lens.
- Instantaneous Field of View (IFOV).: the smallest detail detectable within the FOV. The IFOV determines how much a single detector pixel sees.
- Measurement Field of View (MFOV).: the smallest detail that can be accurately measured. As the distance to the object increases, it will measure accuracy.
Let's clarify the difference between these components using an example.
Suppose you are driving on the highway. What you see through the windshield is your Field of View (FOV). After a while, a billboard appears in the distance. You see the sign but cannot read the text because the distance is too great. That's the Instantaneous Field of View (IFOV). As you get closer, the text does become readable. This is called the Measurement Field of View (MFOV) - the maximum distance to measure something.
Ultramax, also known as super resolution, is a way to increase resolution using software. The camera takes multiple images and overlays them. For example, the device turns a 640×480 image into one of 1280×960. This is an image enhancement, but does not have the same quality as an image from a camera with a sensor whose resolution is 4x higher.
The difference between low and high resolution thermal imaging cameras is immediately apparent with the examples below.
This thermal image was taken with a 640×480 detector:
The photo below is from a 320×240 detector:
What is immediately noticeable is that much more detail is visible in the hi-res photo. It is easier to identify problems. There is also a serious difference in the measured temperatures (78 °C vs. 68 °C).
The difference between different resolutions is even greater in the below measurement of a transformer:
(source images from FLIR ITC)
The resolution of the lower thermal camera is not really suitable for this measurement. The average temperature measured there is drastically lower than the actual temperature due to the cold background radiation from the sky. This would underestimate the severity of the situation.
We can help you determine, what resolution and lenses are needed to make reliable measurements in your application.
The choice is usually determined by a combination of lens and detector, as well as the versatility in which the camera is to be used. A camera may have good accuracy. But if too few pixels cover the zone of interest, an incorrect measurement will still result.
