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Q. What is the difference between high definition thermography and
other types ?
A. Just about all modern cameras
provide high-definition images. The ‘definition’ of a thermogram re-lates to how many individual temperature measurements are taken to build the image. The actual defini-tion is not as important as how accurate and sensitive those temperature measurements are. The higher the definition, the better the picture will look but this does not mean that the accuracy is any better. Describing a thermogram as ‘high definition’ maybe
confusing and misleading as most so-called high-definition images are produced
by software manipulation of the data.
Low definition would be considered below 160 x 120 pixels. Industry standard is between 160 x 120 up to 320 x 240 pixels. High-definition would be considered above this and can be as high as 640 x 512 pixels.
Q. What is resolution? Is resolution important?
A. First, there are a couple of resolutions that apply to IR cameras. There's spatial resolution and there's thermal resolution. Spatial resolution is related to the number of pixels in an image. This is analogous to today's digital cameras and their number of pixels/picture, e.g. 2 megapixel vs. 3 megapixel vs. 4 megapixel, etc. For many or most applications 2 megapixels will provide excellent pictures for most set-tings in fact unless you try to zoom in you would be hard pressed to tell the difference between 2, 3 or 4 megapixels. However, you will find a significant difference in image file sizes and camera costs. The point here is that the 2 megapixel camera will work perfectly well for routine picture taking. Using IR cameras for scanning humans works much the same. (you cant tell the visible difference)
Q. What Field of View (FOV) is best?
A. The focal length of industrial cameras is generally short and using optical lens (25 degrees is com-mon) to zoom in for distance reduces the accuracy by simply making the pixels bigger and reducing the field of view.
For fever screening we recommend the med520 using an 11 degree field of
view which make the tem-perature measurements more accurate at distance. We
do not use an optical or digital zoom lens. We can supply the med520 with
optional field of view, 11 degree, 17 degree, 25 degree, 32, degree. 50 degree
and are happy to advise on the best options for specific requirements.
The
focal ability of the Meditherm 520 with an 11 degree FOV is 1 meter (39
inches) to infinity. The opti-mum focal length for fever screening is 7.3
meters (24
foot). The focal length to stay within specification for fever screening
is 6 foot to 35 foot. (accurate measurements can still be made up to 70
feet
but the area of the face will be so small that sensitivity will be low
due to the number of pixels, ‘individual tem-perature measurements’ on the
face.
Q. Do people have to stand still in front of the camera?
A. Not with the Meditherm 520. People should walk at normal speed and the camera should be facing the people or at most be at 20 degrees angle to the people being scanned.
The frame rate will detect anyone within 1/7th of a second who is moving in the field of view. The alarm will continue the whole time that a person with fever is in the view of the camera, (average time it takes for people to pass by the camera is 15 to 30 seconds).
*If someone runs quickly across the camera it is very possible that the threshold alarm will not go off ......
Q. How do we identify which person is causing the alarm
so he or she can be stopped?
A. The time a person is being imaged as they walk towards the camera depends on how far away they are when we start imaging.... the optimum distance of 7.3 meters (24 feet) can be used as the target area and imaging can begin at 21 meters (70 feet), the time it takes a person to walk from 21 Meters to 2 meters from the camera is the time we have to detect fever.
There is plenty of time to identify a target person, the image on the screen will set off an alarm and circle the person as he or she walks towards the camera. They can be identified and stopped by the time they reach the fever screening station. This works well in practice and has been found to be affective. The software also has a 'freeze frame' mode which saves the image for replay if there is any question about who set off the alarm.
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