Daktronics C44 - Manual (Page 54)

A-2 Infrared Photocells
At ranges within a few feet, the power of opposed scanner blocks makes alignment simple.
However, even at short range, it may be important to optimize alignment, especially if high
excess gain is needed to burn through dirt, dust, steam, etc.
The best way to align a receiver to its emitter at short range is to drastically reduce the
strength of the light signal. This is easily accomplished by placing a diffuser, such as a sheet
of paper or light colored masking tape, in front of the emitter and/or receiver lens.
The following sections have been divided into the two types of photocells used.
A.2 Installation and Alignment; Opposed Beam
Infrared Photocells
Opposed (beam break) sensing which is used at the start line results in the most reliable
sensing system. Opposed sensing is the most efficient sensing mode, and offers the highest
level of optical energy to overcome lens contamination and sensor misalignment. The
effective range for opposed beam photocells is approximately 75 feet.
For alignment:
1. Begin with the emitter mounted securely in place. At ranges up to a few feet, the
receiver may simply be mounted using line-of-sight alignment. At distances beyond
a few feet, loosely mount the receiver opposite the emitter, leaving a means for
movement.
2. If sensing is to be at an exact location, tie a string around the emitter at the center of
its lens and extend it to the center of the receiver lens to make certain that the center
of the beam will intersect the sensing point.
3. Apply power to the emitter and receiver power blocks. The alignment indicating
device LED on the receiver should now be on (steadily or pulsing).
4. If the indicator LED is on steadily, place a diffusing material (paper, tape, etc) in
front of the lens of the emitter and/or receiver. Use enough thickness to cause the
receiver LED to pulse at an easily countable rate (one to five beats per second). Now
move the receiver up/down/left/right (include rotation) to try to increase the pulse
rate. Secure the receiver in the position where the pulse rate is fastest, or in the
center of the area where the alignment LED is on steadily.
5. Increase the receiver sensitivity to maximum. The sensitivity control, located under
the white nylon access screw next to the indicator LED, is a 15-turn potentiometer
clutched at both ends of rotation. To increase receiver sensitivity, turn the control
clockwise with a small flat-blade screwdriver.
6. Place the object to be detected at the sensing position. If the receiver alignment LED
goes off, alignment is complete.
Note: If the receiver alignment LED does not go off when the object is in place at the
sensing position, the reason may be one or both of the following.
A. Flooding: A portion of the effective beam may be passing around one or both
sides of the object. Move the object back and forth to locate the center of the
beam.
B. Burn-through: If the object is non-metallic or has thin walls, there may be too
much light energy for the object to completely block. With the object in place in