The ACL-20 ‘fence’ system was developed and perfected by CSIR (www.csir.co.za and search) over a number of years. In line with CSIR policy, the sole right to market, sell, install and maintain the system was transferred to a private company called PIDS International during 1999.
After completing one major installation in the Middle East, PIDS International closed up shop and the same rights are now held by a new company, Girocon, where the managing director is Neels Englebrecht, who was the driving force behind all the ACL-20 developments at the CSIR. Neels has now resigned from CSIR.
The ACL-20 is a very sophisticated system, and unlike its erstwhile competition (who effectively copied the basic technology) it was never designed for use at a private home but for use on large perimeters around high-security military and industrial sites (eg, Koeberg, Waterkloof AFB).
The ACL-20 makes use of eye-safe (920 nm), active IR beams and detectors to create an invisible security fence, often located within normal exterior security fencing. The units in certain cases have been constructed to look like palm trees or normal outside lights. The major advantage of the ACL is that it incorporates what is now a highly sophisticated neural network. This uses algorithms developed by CSIR to distinguish between false, nuisance and true alarms. For example, the system can identify when a bird flies through the beam - this being a real, but nuisance alarm. Human intruders are easily detected whether walking, running, crawling or jumping, while other objects such as animals and paper bags are recognised with the alarm being suppressed.
The management software includes a colour graphic map of the site (usually based on an aerial photograph), displaying the location of the sensor units and the status of the individual zones and sensors. The alarm indicates in which zone the trigger event has occurred, allowing the reaction team to go there directly.
The operating principle is the use of a multi-active IR beam with zone lengths of 100 m nominal and 200 m maximum. Up to seven beams are used on a 3 m pole height. The operating temperature is -30 to +55°C and the system is protected against rain (up to 100 mm/h), hailstones and wind. An alarm can occur in the event of a lightning strike near a sensor. The ACL-20 offers up to 100 zones and the communications network forms a circle. This means that a single line cut in a zone will trigger an alarm, but communication with all the other zones and sensors remains intact. The standard ACL installation uses sensors mounted up to 2 or 3 m with the poles having an aluminium frame covered by black IR filters.
The system installed by PIDS in the Middle East covered a 15,5 km perimeter and 164 surveillance units (SUs) were required. The system was modified significantly under Neels Englebrecht before installation. For communication, optical fibre cable was used to eliminate the previous problems caused by lightning. The SUs were completely redesigned and each 3 m pole had two 1,5 m high, 180° access panels, for replacement of the lasers or sensors. (Previously the entire tube had to be lifted off vertically.)
Another change made to the SUs is that each one is now intelligent with on-board flash memory and four processors. This significantly expands the capability of the system as each SU can be programmed individually. This is important where, for example, the zone traverses a gate, where different access rules may apply (eg, personnel only or vehicles only). Another important example is where larger wild animals are crossing (eg, going to a water hole), and these alarms can be suppressed at the appropriate times.
The key to the success of the ACL remains its unique knowledge-based neural network operation. This has been honed to perfection over time so that it can even identify the type of vehicle crossing the zone, classifying these as cars, Land Rovers, armoured vehicles etc. In the Middle East case, the large number of zones means that it is possible to detect up to 10 000 events per hour. The neural network system with its object classification reduces this to virtually zero. Another innovation in the Middle East installation was that each PC in the control room was equipped with a strobe light and an audio alarm, eliminating the need for the operator to continually watch the screen. Each alarm identifies the zone where the event occurred and displays an icon of the identified object.
The new installation in the Middle East was programmed so that alphanumerical data could be displayed in either English or Arabic (any language is possible). Another major advantage of this upgraded system is that the software can be upgraded from South Africa using the Internet, and customer problems can be resolved in the same way as local experts can interrogate every SU and module. This significantly reduces maintenance costs as there is generally no need for an engineer to have to physically go to the site from South Africa.
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