13
Functional principle of the joker² light barrier system
Copyright eltima electronic 2022
The light beam
As described, the light barrier emits fast successive invisible infrared light
pulses (one pulse of 10 µs each 200 µs), which are sent back by a reflector to
the receiver. The receiver needs to receive back a certain amount of the emit-
ted light of each pulse. This amount of light is determined during the training
process, see section
. If it changes by a measure that was
defined with the
sensitivity
parameter, the light barrier is considered to
be interrupted and a trigger is reported to the digital part.
Due to the characteristics of the optical components, combined with the re-
flective properties of the retro reflectors the beam path is fairly complex.
However, in a simplified way, it can be explained as follows:
The path between the light barrier and reflector, hereinafter called working
distance, can be roughly divided into three sections.
The middle section marked green is the "normal" working section of the light
barrier. Depending on the reflector and the selected working distance the
effective "beam diameter” is about 2 - 5 mm. An object must cross this beam
in order to trigger the light barrier. This small diameter leads to a very precise
and reproducible switching point of the light barrier.
In the orange section, close to the reflector, the sensitivity decreases and
small objects will no longer be reliably detected because light may be re-
flected around the object.
In the blue area near the light barrier, the outgoing beam from the transmit-
ter, and the reflected beam coming to the receiver are farther apart, result-
ing in a more complex pattern, and less predictability as to where an object
might trigger the light barrier.
In the green area, the two beams are so close together they can be con-
sidered as a single beam.
As a result, the system should optimally be set up so that the subjects will
cross the light beams in the green area, which is roughly the middle one third
to two thirds of the working area.
Figure 13: Sections of the light beam