Thermal camera sensors require precise readings to ensure accurate temperature measurements. Because of this, non-uniformity correction (NUC) is a crucial process to get accurate scans. NUC addresses minor heat fluctuations in the internal components, lens temperature, and lens characteristics, any of which can affect calibration.
NUC plays a vital role in compensating for minor detector drift that often results from changes in the scene and environment you’re working in. The camera's own heat can even interfere with temperature readings.
The Non-Uniformity Correction process
The NUC process counteracts these drifts. A NUC enhances thermal image accuracy by measuring the internal infrared radiation from the camera's own optics and adjusting the image accordingly. To perform a NUC, most IR cameras temporarily block the IR optical path inside the camera by swinging a shutter component with a flat, high emissivity surface in place. At this moment only the shutter is visible by the detector. By capturing temperature data of this shutter, the camera can adjust gain and offset for each pixel resulting in both a higher quality image and a more accurate image.
With some cameras you may hear a clicking sound for a moment as the shutter swings into place. This is normal and during a NUC the image on screen will freeze momentarily.
When you turn your thermal camera on, it will probably start up with a NUC immediately. The camera will then keep performing a NUC periodically, as the camera senses changes to the environment in an effort to account for minor drift. As the camera hits a stable operating temperature, the NUC process will happen less and less often. While it is possible to start taking thermal images almost immediately after powering on the camera, it's best to allow your camera some warm-up time. If you can, let the camera sit for around 20 minutes in a stable environment to achieve optimal temperature measurement accuracy and image quality.
Non-Uniformity Correction and Fluke TI cameras
Fluke TI Cameras automatically perform a NUC about every 60 seconds once turned on and stable. It’s possible to manually initiate a NUC even when the camera doesn’t sense that it is necessary. Although this is usually not necessary, it does allow you to force a NUC to occur without waiting for it to happen automatically. One instance that might warrant this is when moving to a temperature environment which is much colder or hotter than the one the camera stabilized in and wanting to immediately capture IR images. In that instance the NUC provides the best image and accuracy.
In most Fluke cameras, simply press the power button once briefly during operation to initiate a NUC.