When cooled infrared thermal detector is working, its cryocooler works first to reduce the temperature itself, so that the sensor has higher sensitivity, higher precision, smaller error and wider detection temperature range when detecting a target. Due to its high precision, small error and high sensitivity, the cooled thermal imaging camera makes more reliable detection results. While from this point of view, uncooled infrared thermal sensors cannot reach such standard, especially the non-uniformity of uncooled infrared focal plane array has a great influence on the measurement error. Besides, there are some other technical differences as follows:
1) Relative aperture (F number)
Uncooled infrared focal plane detectors lower the barrier to entry for thermal imagers. When comparing cooled and uncooled thermal imagers, attention needs to be paid to relative aperture (F-number) and conditions of use.
The relative aperture of a thermal imager is determined by the F-number of the infrared focal plane detector. Typical relative aperture numbers for cooled focal plane detectors are 1 to 4, while uncooled focal plane detectors have a typical F-number of 1. In other words, an infrared telescope with a large aperture is required to concentrate more infrared radiation energy to the detector.
2) Response speed
Cooled focal plane detectors are photon detectors with fast response speed (on the order of 10-6 s), and general uncooled infrared focal plane detectors are thermal detectors with slow response speed (on the order of 10-3 s). The performance of the cooled focal plane detector decreases rapidly with the increase of the frame frequency. For example, when the frame frequency reaches 200 Hz, the performance decrease is not obvious. At 100 Hz the thermal sensitivity of the detector drops considerably.
3) Conditions of use
The detection rate of the general cooled infrared focal plane detector is 2 orders of magnitude higher than that of the uncooled infrared focal plane detector. When the performance of detector elements reaches a certain value, the number of detector elements plays a major role in the detection of extended source targets, and the difference in detection rate is not obvious. But when detecting a point source target, the target converges on the focal plane detector to be only one image point, and the detection rate plays a decisive role at this time.
4) Volume, weight and cost issues
In order to detect long-distance targets, an infrared telescope with a long focal length, such as 150 mm, is required. Since the typical value of the relative aperture of the uncooled infrared focal plane is 1, it is made of expensive germanium single crystal material, and the aperture of the infrared telescope objective lens will also be 150 mm, so the reduced volume, weight, and cost of using an uncooled infrared focal plane detector may be offset by the increased volume, mass, and cost of an infrared telescope.
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