Non Uniformity Correction
Tip written by: Infraspection Institute
Focal plane array detectors are standard components for most commercial thermal imagers. One feature common to all FPA imagers is a function known as non-uniformity correction.
Using an FPA detector in the construction of an imager provides high resolution and other advantages. One disadvantage is that FPA detectors tend to “drift” during imager operation. When the pixels of an FPA detector drift, their response to the radiant energy emitted by an object changes.
As an FPA detector drifts, the displayed image will develop areas with inexplicably hot or cold pixels. Drifted pixels cause the appearance of hot/cold artifacts within the image and cannot be relied upon for accurate temperature measurements. Depending upon imager type and ambient conditions, significant drift can occur within a very short period of time.
To correct for drift, all FPA imagers have a function known as non-uniformity correction. Simply put, NUC is a feature that ‘resets’ the image by aligning all detector pixels to the same value. Depending upon imager model, the NUC process may be an automatic feature of the imager or a manual function performed by the thermographer. Performing a non-uniformity correction may require several seconds to complete; during this time imaging is not possible.
During the NUC process, a high emittance object of uniform temperature is temporarily placed within the optical path of the imager. When the NUC process is activated, the imager’s computer electronically adjusts the gain of all detector pixels to a uniform value thereby removing errors caused by detector drift. A NUC should be performed at regular intervals during imager operation or whenever hot/cold artifacts appear within the image.
Infrared imager operation is one of the many topics covered in the Level I Infraspection Institute Certified Infrared Thermographer® training course. For information on our open enrollment or Distance Learning courses, please visit us online at www.infraspection.com or call us at 609-239-4788.
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