The heavy duty laser light
barrier systems HLS are in worldwide operation since 1987.
The HLS systems have a maximum range of approx. 800 m and
are suitable for long range perimeter protection and applications
in industrial environments, where adverse conditions like
dust, smoke, steam or heat prevail.
A laser light barrier system HLS comprises a transmitter
unit and a receiver unit. The transmitter unit contains
an eye-safe semiconductor laser device, which emits light
pulses at a fixed pulse repetition rate, as long as the
supply voltage is applied. The receiver unit contains a
highly sensitive photodetector and an integrated alarm relay.
When a system is aligned and switched on, the emitted light
pulses are picked up by the
photodetector in the receiver unit and the integrated alarm
relay is switched to the ‘Alarm Off’ state.
The use of a semiconductor laser transmitter and a highly
sensitive photodetector guarantees reliable operation, even
under extremely difficult conditions. Due to a high quality
optical filter in the receiver unit, even high background
illuminations, resulting from direct sunlight or white-hot
steel, does not effect functionality.
If the connection between the transmitter and receiver is
cut off by an object moving into the optical path, or if
there is a technical defect in the electronics or in the
power supply, the alarm relay is switched to the ‘Alarm
On’ state.
Receiver units are available in three different versions,
to cover diverse requirements.
The receiver HLS offers a variable alarm activation time,
which can be individually set from about 10 msec to 1 sec.
By setting an individual alarm reaction time, it is possible
to avoid false alarms and consequential costly interruptions
of production, due to the loss of a few light pulses, not
relevant to functionality.
Increased operational safety is offered by the receiver
HLS-K. During operation in adverse environments, the optics
of the transmitter and receiver units will in time inevitably
be covered by a layer of dust or a dirt/oil film reducing
the initially high power margin. When the received optical
power decreases to near the detection threshold of the photodetector,
even small changes in operating condititions might result
in pulse losses provoking false alarms and again costly
interruptions.
To avoid this, the HLS-K receiver features an independent
‘Pre-Alarm’ function. If the strength of the
continually received optical signals fall below an individually
adjustable threshold, an independent ‘early warning’
signal is activated, alerting the maintenance staff. By
setting the ‘Pre- Alarm’ threshold with a sufficient
margin to the fixed ‘Alarm’ threshold, false
alarms can be avoided and maintenance cycles kept to a necessary
minimum.
The receiver HLS-T is aimed at applications, depending on
very short reaction times, offering a fixed alarm activation
time of 2 msec.
The careful selection of materials and components and the
use of rugged stainless steel housings and armoured silicone
cables, ensures troublefree operation even under most severe
conditions. For operation in areas of high ambient temperatures,
all devices can be delivered in a special double-walled
housing with pipe-fittings for the connection to an air
or water cooling circuit.
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