A mechanical zero adjustment can be made within the limits given in Sensor rangeability. It is possible to make a zero adjustment with the sensor in-line. For mechanical zero adjustment, remove the image detector module according to the instructions in section sensor disassembly.
Near the tip of the Image detector module (Figure 1) there is a fiber optics holder (C) and 2 adjustment screws. The 2 screws work against each other in a push and pull configuration. The locking screw (A) pushes the holder inwards and the adjusting screw (B) pulls the holder outwards. A combined push-and-pull force locks the holder.
To adjust, first loosen the locking screw (A) carefully. Then adjust the position of the fiber optics holder. To decrease CCD value and measure higher concentrations, turn the adjusting screw clockwise. To increase CCD value and measure lower concentrations, turn the adjusting screw counterclockwise. When the position of the fiber optics holder (C) is correct, lock it into place by tightening the locking screw (A) gently. Be careful not to bend the T-shaped holder (C) by forcing the locking screw too far in. The visible part of the holder should always be in horizontal position.
After the mechanical zero adjustment, check the optical image.
If the sensor cover is removed, ambient light disturbs the CCD signal.
