Understanding Electronic Perimeter Protection

By John Bigelow.

Perimeter security can be tricky at the best of times. Unlike indoor intrusion detection, where one can control the environment with a reasonable degree of certainty, perimeter detection requires one to account for a great many variables such as ambient light, wind, rain, wildlife and other naturally occurring factors such as falling branches or wind swept rubbish interfering with sensors.

In addition to environmental considerations, one must also consider the aesthetics of any solution. A 10-foot high electric fence spaning hundreds of metres and topped with coils of razor wire, while undoubtedly creating an effective barrier to entry, may not fit the design scheme for the surrounding area. Such a solution might be appropriate for protecting a detention centre or power substation for example, but may not provide the type of look one might seek to achieve for a high-end marina or estate.

In these types of applications, one might instead search for a less visually intrusive method of perimeter protection such as photo-electric beams. However, in recent years, there has been a degree of scepticism from some areas of the security market around the use photo-electric beams. These concerns arise from such claims as the belief that photo-electric beams can be easily defeated or circumvented, or false alarm too often, and so on. To get to the bottom of these claims, we spoke with Tom Kinkade of Takex, one of the world’s foremost suppliers of photo-electric security solutions.

Tom began his career in the security industry back in 2000 a technician with Cage Security before moving into the wholesale side of the industry in 2003 with Video Security Products (Formerly Kobi Security), where he worked as technical support and sales from 2003-2007. Tom joined Takex in 2008 as a sales rep where he quickly rose to his current position of national sales manager.

With regard to the misconceptions around photo-electric beams, Tom explains that beams are not different to any other security product such as a CCTV camera or a PIR detector, in so far as many end users fail to understand that there are significant differences between high-end and low-end products in the market, focussing on price rather than performance. One of the great things about our company is that Takenaka are very conservative about performance claims versus the real capability of the product. This modest approach gives our long-term customers huge confidence in our brand”, explains Tom.

“It is easy to make something look good on paper. How it performs in the real world, however, is an entirely different matter.

“Some people have been lead to believe, for one reason or another, that a photo-electric beam is a less secure form of perimeter protection because it can allegedly be defeated by using a simple substitute light source such as a torch or television remote. The reality is that while this might be the case with some photo-electric detection solutions, this type of tampering will not work on properly designed and engineered higher-end products. Takex have been leading the industry in this area for over 20 years.”

Another common concern regarding the use of photo-electric beams is the alleged frequency with which they false alarm. According to Tom, in 99 out of 100 cases, such issues arise as the result of either a poor installation or inferior product.

“What many people, including some installers, fail to realise is that it is possible to completely botch the installation of a photo-electric beam and yet still have the beam appear to be functional.

“A photo-electric beam works by transmitting light from one tower and is received on another tower. Despite what we see in movies, the light is not a laser beam that maintains a consistent pin-like narrow focus across the entire distance between the two towers. Instead, the light tends to fan out as it travels between the transmitter and the tower. If you could see the detection area, it would look more like a type of banner.

“The receiver only needs to see one per cent of that light beam in order to work. If an installer incorrectly aligns the beam, it is easy to create a situation where a disturbance such as rain or fog will cause issues. A photo electric beam is no different to any other security product in that correct installation makes the difference between a product working the way it is intended to work or not.”

Tom goes on to explains that “the environment in which the installation is taking place will also impact on the effectiveness of the beams, as will the distance between towers and the number of beams being installed. Where the transmitter and receiver are between 100 and 200 metres apart, (100 metres is the optimal distance for high security installations) and if the installer is using a quad beam (meaning four beams in the one sensor), the likelihood of a false alarm is virtually non-existent. Of course, this is also dependent on the client using a quality product which has been properly and professionally installed by a qualified installer.”

Another common misconception seems to centre on the idea that if a person moved fast enough through the beam (running and diving as fast as possible), the sensor may not recognise the interruption as a person and therefore not trigger an alarm. According to Tom, this is not the case.

“A photo electric beam is literally a beam of light. Once the beam is broken, it is broken. As I explained earlier, the beam tends to fan out and become wider as it projects from the transmitter to the receiver. Beams are also supposed to be set up so that you have a combination of transmitters and receivers on each tower so that the beams crossover. Whether or not an alarm is triggered will depend on a number of factors including the amount of time the beam is interrupted for and the percentage of the beam that is broken.

“If you were to take your hands and hold them up in front of you with the fingers spread and palms facing towards you, and then place the little finger of the top hand in between the index and middle finger of the bottom hand, you get a rough idea of coverage of the beams if you imagine each hand represents a beam projecting in opposite directions. With your hands in this position, if you imagine something were to pass through one of your fingers, such as a bird, leaf or small animal, then the system should not alarm.

“If a person tried to move through the beam, even very quickly, you would find that even through the beam only registers a brief interruption, because it occurs across, in our example, three of four fingers, a large enough percentage of the beams have been broken to trigger an alarm event. Conversely, if someone tried to crawl through the beam to minimise his/her profile, their slower speed as they transition through the beam will result in an alarm being triggered.

“Photo electric beams do not rely on just one set of input data, they use multiple inputs – size, transit time and so on.”

Another way to imagine it might be a series of banners, in the case of a quad beam, four banners, each around 500mm tall, running between the towers. A leaf or bird flying through a banner is not enough to cause an alarm. It requires a significantly larger mass to trigger an alarm condition.

Like so many things in life, many of the concerns around photo-electric beams stem from ignorance and a misunderstanding with regard to the best and most effective way to install the beams and the differences between lower-end products versus high-end products.

When used correctly, photo-electric beams can create a very effective, and unobtrusive, security perimeter capable of spanning significant distances.

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