Every infrared camera defines its Field of View (FOV) across a horizontal/vertical axis.
You have two ways to determine the Field of View (FOV) on your camera:
1. You can calculate the FOV
2. You can measure the FOV with a practical field test
This maintenance tip describes the Practical FOV Test.
The Practical FOV Test is a quick method to determine what can be seen at set distances with your camera, the lens, and IR Windows.
1. Find a long countertop or a 6 foot folding conference table. Lay a piece of plain butcher paper along the length of the table.
2. Set the camera on the table and mark a "zero" line across the table width. This zero line should be far enough on the table so that the camera cannot accidently fall off the table. The zero line is where the camera lens touches the line.
3. Draw a straight line the length of the paper along the center.
4. Intersect this line with lines at 6 inch increments from the zero line.
5. Label the lines from 0 to 36 inches. You can go further if you have a panel depth deeper than 36 inches, but usually 36 inches is sufficient.
6. Place the camera lens at the zero line with the straight line going down the center of the paper in the middle of the camera lens.
Now, it is time for a coffee break. Not really, you need two heat sources. Some people use coffee cups - good excuse for a break. You can use any known heat source. Some people use hot plates if they are in a lab, a griddle, or you can purchase inexpensive candle warmers.
7. Place the two heat sources at a distance from the camera that is typical of the targets you will monitor. For example, if your targets are 18 inches from the panel, then place the two heat sources at the 18 inch mark.
8. Move one heat source from the center until it appears just inside the edge of the image in the camera display.
9. Move the other heat source in the opposite direction until it appears just inside the camera display on the other side.
The distance between your two heat sources is the maximum FOV using your camera and lens. At the defined distance.
10. You can draw a line from each side of the camera lens at the zero line to the heat source on the same side. This gives you the FOV for any distance from the zero line to the heat sources.
11. If you are using an IR Window, subtract the camera lens diameter from the FOV. Next add the diameter of the IR window. This gives you the Maximum Horizontal Window FOV. For example, you have a FOV at 18 inches on the center line of 8 inches. The camera lens is 1.75 inches. The camera FOV is then 6.25 inches. If you are using a 4 inch IR Window, then add 4 inches for a total Maximum Horizontal Window FOV of 10.25 inches.
You can repeat the above process with the camera lying on its side to determine the Vertical FOV.
When finished, roll up the paper and save for future reference.
You can create a table for the distances along the center line and the Horizontal and Vertical FOV for different window sizes in your plant.
Also, while you are at it, use your heat sources to adjust the camera settings to compensate the IR Window transmission rate.