What is the "click" sound?
The clicking sound is normal in microbolometer-based cameras. It is the result of the camera's non-uniformity correction, or NUC. What you actually hear is the camera's internal shutter moving in front of the detector for a brief instant.
This occurs regularly in uncooled infrared chambers, but also occurs occasionally in cooled infrared models.
It is also known as FFC, which stands for flat field correction. The shutter is a flat source for the detector to calibrate itself to give a uniform response.
What does a NUC do?
Non-uniformity correction (NUC) adjusts for the small detector drift that occurs as the scene and environment change. Basically, the camera's own heat can interfere with temperature readings. To improve accuracy, the camera measures the IR radiation from its own optics and then adjusts the image based on those readings.
The camera usually freezes the image stream when this occurs. Otherwise, you would see a completely flat image.
What happens without the NUC?
As mentioned above, the NUC is useful for improving temperature readings. Without the NUC, there is a risk of unstable temperature readings. The NUC cannot be disabled on most portable cameras.
However, in most automation and science units, the NUC can be set from automatic to manual mode. This will allow you to control exactly when the camera performs a NUC, either through software or hardware signals.
After initial start-up, the camera will perform NUC frequently. The image may freeze momentarily and a "click" may be heard. As the camera warms up and reaches a stable operating temperature, NUCs will become less frequent.
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