eltima electronic Jokie 2, User Manual

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Functional concept
The light beam
As described above the light barrier emits quickly succes-
sive invisible infrared light impulses, which are reflected by
a reflector and get back to the receiver. The latter expects
a certain minimum amount of the emitted light back for
each impulse.
While using the light barrier with a reflector, the received
amount of light is above a fixed threshold and the LED is
off. If the amount of light is below the threshold because
an object weakens the light beam or one impulse is miss-
ing since a large object is in the way of the beam, the LED
lights up and the connected device is released.
Due to the sending- and receiving characteristics of the
optical components, combined with the reflection charac-
teristics of the reflectors, the working distance between
the light barrier and the reflector can be roughly divided in
three sections.
The green middle section is the “normal“ working area of
the light barrier. Depending on the reflector used and the
working distance, one can assume a diameter of the beam
of 3-5 mm. The objects to be detected be the light barrier
need to meet and interrupt this beam. The small diameter
brings a very precise and repeatable switching point of the
light barrier.
The sensitivity of the system is highest in the green area.
In the orange area, closer to the reflector, the sensitivity
decreases and it's not sure that smaller objects will be de-
tected.
In the blue area that is close to the light barrier objects
may work as reflectors themselves. Therefore its is possi-
ble that a bright, well reflecting object may reflect the light
better than a reflector that is far away. As a result of that
the threshold value mentioned above is not undershot and
thus the light barrier not released, although an object is
positioned in the light beam. For that reason the light bar-
rier should be set up so that the object do preferably not
move through the blue area.
Consequently the light barrier can be operated without a
reflector in the blue area, which may be a great advantage
in some cases. The reach of the light barrier then depends
basically on the size and the reflection characteristics of
the object, see section Taking pictures without reflectors .
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© eltima electronic 2013
Image 7: Sections of the light beam