Shutter

In the field of optical devices, a “shutter” is a mechanism that interrupts the optical path of those instruments for various reasons. There are shutter mechanisms used in different positions between the optical components and the radiation-sensitive detectors. At the entrance of an optical device like a pyrometer or imager, a shutter can be used to protect the expensive optical components against dirt or mechanical damage when the device is not in use. During the brief time interval when a periodically present object occurs, the shutter opens the optical path to allow the measurement. After that measurement, the shutter can close again until the next object is present. A good example of using a protection shutter is in float glass hardening facilities, where hot glass sheets move over rollers for less than one minute after being in the oven for 15-20 minutes. During these intervals, the shutter remains closed to keep the optics clean.

Mechanical shutters are widely used inside temperature measuring imagers to normalize the output of each pixel to the others and to compensate for the ambient temperature drift of all pixels in the installed detectors. These integrated shutters in Optris imagers are usually called “flags” because of their special design. When the flag is closed, all pixels receive the same amount of radiated energy from the flag surface, which has a very high emissivity and a known temperature. This reading from all pixels of the focal plane array is stored as a “dark image” and is subsequently subtracted from each image taken from the outside scene.