Join the AIR force

As with many industries we have seen a change in the use of technology and Active Infrared Beams (AIR) is no exception. In recent years the use of AIR technology has in some instances been replaced by passive technology where savings on installation and equipment appear attractive and performance has been acceptable.

As these external detection markets grow several factors become evident. Performance becomes more critical, the attitude of the police, regulatory authorities and monitoring companies becomes more focused and the application becomes more widespread. As a result, the demands on product performance have been steadily increasing: 'catch' performance is critical, but false alarms are not acceptable.

A crucial influence in the reduction of false alarms is better control of the detection area. AIR technology provides a controlled detection pattern and can provide reliable detection with minimal false activity in a wide range of applications. Locations where passive technology requires a significant compromise on catch performance to provide acceptable false alarms are becoming more common as the application on external detection increases.

Point-to-point detection

Most installers have traditionally used Active Infrared Beams in simple 'point-to-point' applications, and they tend to work very well. Indeed in certain applications, in a limited field for example where they can be readily installed and configured, they have proved extremely reliable.

They have tended not to work so well, however, in more complicated installations when multiple zones are involved - the big issue being one of 'cross-talk' and the possible likelihood of false alarms and or missed alarms.

An active beam is, in effect, an invisible light source transmitted from one point and collected by a receiver at the next. Their detection range can be typically up to 200 meters, and the detection height dependent quite literally on how many units are installed. How they work is simple: dual beams are transmitted via the top and bottom heads to the dual head receiver, and it requires both beams to be 'broken' in order for an alarm to generate.

But there are problems: the sun, for example, generates large amounts of active infrared which means careful adjustments to the viewing angle of the receivers such that they only 'see' the light source from the intended transmitter.

Transmission frequency is also an issue: receivers need to have a tight viewing spectrum such that they only respond to IR they expect to see from the transmitter.

IR Power – or to be more specific the regulation of power – is another consideration. Too much power, for example in ideal conditions, affects beam performance due to reflections. Metal fencing seen at a particular angle can look like a solid metal wall and reflect accordingly, bouncing around an intruder. Too little power at the wrong time (ie, in poor weather conditions) and it won't see anything at all.

Conventional active beam detectors are often 'stacked' inside towers (for example a three metre tower would comprise 4 x beam 'sets' for optimum coverage) requiring separate coded channels for each beam. But that in itself causes another headache for the installer: each receiver needs to be synchronised, and know to which transmitter it is being 'paired'. If it doesn't, then cross talk, false alarms or missed alarms can occur with the resultant fall-down in the system's integrity.

Conventional beams also suffer from 'over-ranging', effectively passing their designated receiver and being picked up by other devices (a beam's arrival distance in good conditions can sometimes be ten times its stated range!). Two signals going in to the one receiver means that the genuine signal cannot be determined, and the effectiveness of the beam is negated; it won't see the 'real' signal and therefore won't see the real intruder!

Individual addresses

New photoelectric digital detectors are now available whereby individual addresses are assigned to each pair of beams. This allows all essential information (eg, power status levels) to be communicated digitally, but more importantly it enables the receiver to 'learn' the digital packet block of information it should expect, and to ignore all others. This therefore removes the possibility of subverting the system.

Manufacturers have also found ways of fitting their detectors with various power regulators that automatically controls, adjusts and optimises the amount of power to the beams such that performance can be maintained. The result is a reduction in the number of false or missed alarms caused by fluctuations in beam quantity influenced by outside elements. This includes excessive IR beam signal caused, for example, by reflection and poor beam quality as a result of dense fog.

Timing devices are also now being used to further ensure that beams do not overlap, and to reduce the likelihood of false alarms when multiple detectors are installed or set up at multiple stages. With new digital systems, transmitters can be synchronised in stacking installations such that the beams are transmitted sequentially, top to bottom, rather than all in one go. Again this prevents the beams from colliding, or inadvertently finding the wrong receiver; beams also now actively 'look' for their correct receiver - and if they cannot find it, then they go into alarm.

It is not just the products' technology that has improved. Manufacturers have also been listening to installers in terms of ease of installation. Dual alignment level indicators, for example, have now been incorporated to include a peak finder. A peak finder interface contains two tuning modes: a rough tuning mode, and fine tuning mode. After roughly adjusting the beams, the lowest and the peak of the received beam level is searched for repeatedly. This allows the accuracy of the beam to be at its optimum level.

Within our own range of detectors specifically, there are a few further improvements that we have made to improve an installer's lot. A beam-blocking tool is no longer required since adjustment to both upper and lower beams can now be made simultaneously. And there are physical improvements too: an integrated chassis and installation plate; anti-frost head cover; manufacturer to IP65 etc.

Installers have been understandably wary of Active Infrared Beams for some time, especially when it comes to using them in more complex installations with multiple zones. Issues with cross talk and other factors adversely affecting performance have meant that they had had little application beyond the most straightforward of installations, where their performance is at its best. The new generation of detectors, however, might mean that it is time to give active beams another go.

• Optex has over 25 years experience in the field of infrared detection devices and specialises in the production of both active and passive infrared sensors for intruder and event driven CCTV applications. Optex (Europe) Ltd was established in Berkshire in 1991 to develop markets in the UK and Eastern Europe.

www.optexeurope.com.

Tel 01628 631000