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Perimeter beams explained

Ernest Mallett, product manager at ADI Global Distribution, answers common questions on perimeter beam issues.

Ernest Mallett

When installing beams should I use a ‘Twin’ or ‘Quad’?

The site and the application requirements will help you define which beam technology you should choose. Twin beams are generally smaller and rely on two beam paths to be broken to generate an alarm; quad beams form a lattice of 16 beams which need to be broken making them more reliable over long distances.

What distance can a beam cover?

When mounted externally standard twin beams can cover up to 100 metres and quad beams up to 200 metres. However, when standard beams are mounted internally manufacturers generally double the coverage distance, ie, an external 50 metre beam can cover up to 100 metres internally. Beam manufacturers tend to refer to the coverage distance as part of their model number.

Do you need power to both the transmitter and receiver of a beam set?

With active beams, power needs to be supplied to both ends. Generally beams require 12~30 V d.c. and the transmitter and receiver can be run from different power sources. For distances up to 11 metres in external applications a reflector beam can be used, which only requires power at one end.

Will birds or small animals set the beams off?

This is highly dependent on the installation site. Quad beams offer much greater protection against false alarms as most beams have adjustable break timing which allows differentiation between fast moving objects such as birds, litter and small animals and a genuine intrusion.

I have never fitted beams before; how easy are they to fit and set-up?

Most beams are equipped with devices to help easy setup such as optical viewfinders, LEDs, alignment tones and monitor points, allowing for fine-tune alignment using a voltmeter. Manufacturer instructions are generally very clear and easy to follow when installing beams. Manuals will include sections: how to mount beams, the beam setup, the Do’s and Don’ts, as well as a fault guide.

A useful tip: when you are working on the longer-range beams, hang a Hi-Vis jacket on the receiver when aligning the transmitter as the jacket will be much easier to spot through the viewfinder than the black beam unit.

How are beams mounted and are there advantages of putting beams in a tower?

Beams may be mounted on a pole, flat surfaces or within specially constructed towers. Some beams will come with a pole mounting kit included. The pole can be up to 43 mm in diameter – normal industry standard scaffolding poles will be sufficient to mount the beams.

Towers may be used where it is difficult to mount a beam, in open areas for instance. They are constructed in such a way as to give no external indication to the casual passerby about the number of beams housed within. Towers come in different heights to accommodate the required number of beams. In exposed or adverse and cold weather locations towers may be fitted with a thermostat and individual beam unit heaters to ensure constant operation.

I have a requirement for multiple beams mounted on top of each other to form a fence. Will they not interact with each other being so close?

The interaction of beams is called crosstalk. Selecting intelligent multichannel beams will reduce this and allow you to select the frequency for each pair of beams so as to not interfere with an adjacent set.

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