by raceamerica » Tue May 12, 2020 12:34 pm
There are a few facts to know on the operation of the start beams.
First, the detection beam between the emitter and sensor is always a straight line. This is true even if the enclosure is 10 degrees off angle to the track. As long as the sensor can see the emitter, the beam is a straight line in the center of the holes of the enclosures. When aligned, the start beam enclosures may not necessarily be parallel with the track edge to be properly aligned, especially with multi-beam units like start beams.
Second, once the beam is locked in, the detection width is very small, under a 1/4 of an inch wide which means a pencil could almost be used to block the beam between the emitter and sensor after they are aligned.
Third, aligning the enclosure is not aligning the beams. Too many times track managers use laser beams mounted on the enclosure to align the start beams. They are assuming the laser beam is exactly parallel with the actual infrared beams. This is usually not the case, especially in multi-beam units like start beams. The alignment process is aligning two beams designed to be slightly off angle to each other.
Also, when building a housing to hold the start beams, there must be provisions to adjust the orientation of the start beam enclosure inside that housing. Once the alignment of the beams is complete, the start beam enclosure can be secured inside the housing.
The sensor has a viewing range of 8 degrees and the emitter sends the beam out as wide as 30 degrees. This is why the enclosure can be rotated to the left and right and the beam stays aligned. It is still a point to point beam from emitter to sensor or in a dual beam start beam, two point to point beams in parallel.
To properly align the beams, place the stage beam on the starting line. Go into align mode on the timer.
Aligning the beams involves rotating the enclosures (as viewed from overhead) around an axis located at the center of the enclosure always maintaining the stage beam on the start line. Do not slide the enclosure up and down the track edge, this will move it off the start line and alignment will be more difficult.
Since the sensor (cabled unit) has a smaller angle of viewing (thus smaller adjustment angle), rotate the sensor first to find the alignment limits. Rotate left to find the angle where the alignment falls off, then rotate right to find the angle where alignment falls off. Center the enclosure between these two extremes. If you cannot find a point where both stage and prestage are alignment at the same time, position the sensor enclosure to the optimum angle. Next adjust the emitter enclosure (battery powered unit) in the same manner, rotate left, then rotate right and center in these angle extremes. To fine tune, go back to the sensor and repeat the same alignment process and rotate very slowly in both directions. You will find the angle of alignment is now much greater.
You will find the emitter side will bring in the alignment once the sensor side has been positioned in its best rotated position. Generally, the enclosure will be anything from parallel to the track edge, to rotated a few degrees. This is due to the tolerances of the circuitry mounted in a formed internal enclosure times two beams. If you find the final 'best' position of the enclosures is 15-20 degrees off, there might be a problem with the emitting or sensing component inside and the start benas should be sent in for inspection (ship both emitter and sensor pair).
You can now understand why a rigid mounted start beam inside a protective housing will make alignment more difficult unless the housing can be rotated for adjustment. The up and down angle of the front of the enclosure (side where the holes are) is not a critical adjustment. If you find this needs adjusting, either the enclosures are not level or the beam need to be send in for inspection.