Daktronics C44 - Manual (Page 53)

Infrared Photocells A-1
Appendix A: Infrared Photocells
A-1 Introduction to Infrared Photocells
Reference Drawings:
Infrared; Emitter/Receiver w/Stand 10 O ...................................... Drawing A-47264
Infrared Cell; Emitter/Rec. w/Stand 6 O ........................................ Drawing A-47265
Drag Strip-Infrared Cabling Diagram........................................... Drawing A-56251
Dual Lane Drag Strip w/C44 ....................................................... Drawing B-91012
Field Cabling; Per Dwg. B-91012 .............................................. Drawing B-114631
Drawing B-91012 shows a cabling diagram of a typical drag strip using infrared photocells.
It is intended to be a guide in locating and running cables to the photocells.
Drawing B-114631 shows the cabling connections.
The terminology “Emitter” and “Receiver” are used with the opposed beam photocells. (Light
is emitted from one and received into another unit.) The term Emitter/Receiver is used with
the retro-reflective type photocell. (A photocell which lights from the Emitter is reflected
back to the Receiver. Both Emitter and Receiver are inside the same unit.)
Details of the different infrared photocells and their mountings are given for reference,
Drawings A-47264, and A-47265.
Notes About the "Effective Beam"
The size of the lens of the emitter and receiver of an opposed sensor pair determines the size
of the pair's effective beam. The effective beam may be pictured as a rod that connects the
profile of the emitter lens to the profile of the receiver lens. The effective beam is the
"working" part of the photoelectric beam; it is the portion of the beam which must be
completely interrupted in order for an object to be reliably sensed. It should not be confused
with the actual radiation pattern of the emitter, or with the field of view of the receiver. The
effective beam size of a photocell pair is one inch in diameter.
Notes About the LED Indicator
An exclusive built-in feature that permits optimum alignment and continuous monitoring of
the photoelectric system. The red receiver LED indicator is on when the receiver sees the
modulated light from the emitter LED and off when the beam is broken. In addition, a low
frequency pulse rate is superimposed on the LED indicator. When alignment is marginal, the
pulse rate will be about once per second (indicating an excess gain of 1). As alignment is
improved, the pulse rate increases, indicating increased excess gain. Optimum sensor
alignment is indicated by the fastest pulse rate.
This feature also signals when maintenance is needed. Any pulse rate less than two or three
beats per second indicates marginal performance, even though the units are still functioning
properly. Whenever the pulse rate is slow, the lenses should be cleaned and/or the alignment
checked.
If the alignment indicator on the receiver appears to be on steadily with no pulsing evident, it
is actually pulsing at a rate that is too fast to be seen. A steadily on LED indicates an excess
gain of at least 20x.