What our experts say…
The Darwin 4 active infrared beam barrier only covers the perimeter – but surely that is the first line to defend! It is available in four different lengths from 0.5 to 2m, to provide adequate coverage of either door or window openings. With an internal range of 12m, it will cover complete walls which may include several openings, including patio doors. Outdoor operation is possible up to 6m range, but additional weatherproofing is necessary.
Active infrared detection systems are less prone to false alarms compared with their passive cousins, since they operate at levels of light energy which far exceed disturbance levels caused by draughts and radiator outputs. Premises protected by active IR perimeter systems will allow free movement and ventilation within the set area.
We looked at the Darwin 4 which comprises separate transmitting and receiving beam columns, each 1m high with four coded IR beams. The actual transmitting and receiving elements are spaced 250mm apart, but the number and positioning are completely hidden from external view, reducing the chances of reaching through between the beams.
The transmitting and receiving towers each employ microprocessors for controlling beam synchronisation and alarm management. An alignment evaluation test is included, to provide a confidence check for the installer.
Alarm output is given via a solid relay (rating not specified) and the response time depends on the manner in which the beams are obstructed. If a single beam only is obstructed, the output is delayed by two seconds; one second for two non-contiguous (non-adjacent) obstructed beams; 0.1 second for two contiguous or all beams obstructed. Bits of flying debris should not cause a false alarm, nor birds, providing they are not in hover mode.
Should an insect park directly over a trans-mitter or receiver element, blocking direct line IR energy, an anti-insect feature changes the beam configuration to avoid generating a false alarm.
Tamper protection is provided at one end of each tower only – the end at which the cable is connected.
Construction
Each column consists of a single extruded, hollow aluminium tube with internal guides throughout its length for supporting the PCBs and an external recess for the plastic IR transparent window strip. The columns are very rigid and not prone to twisting.
When installed, each column is located on top and bottom plastic bases and held firmly in place by two plastic end covers with single securing screws. The bases have a rear cable entry provided and a thin optional cut-out access for surface wiring.
The Darwin 4 transmitting/receiving columns each have two PCBs, 500 x 20mm. The main PCB carries the terminal connector block, microprocessor, tamper switch and two transmitting/receiving elements. The continuation PCB has a ten-pin connector to the main PCB and two transmitting/receiving elements. The high quality PCBs are very well supported over their entire length and each is held in place by a single screw.
Overall, the design and construction are neat and simple, and with each column having a cross-section of approximately 23mm square, the installed system is quite unobtrusive.
Installation
The most critical part of installing the Darwin 4 is accurate positioning of the upper and lower plastic bases. The method is set out in the Installation Manual, using the aluminium column as a marking template. The last screw can be inserted only with the column removed, since it is obscured by the column. It is a good idea to temporarily fit the column to re-check base positioning before inserting the last screw.
The PCBs are not removed during installation and care must be taken to avoid damage to the terminal end of the main PCB since 55mm of it protrudes beyond the column into the base and must be hooked under latches in the appropriate base. The method is shown pictorially in the manual. Other recommendations include: both transmitter and receiver terminal blocks mounted at the top or both at the bottom; and the receiver column mounted such that it is not exposed to direct sunlight.
Six-core normal alarm cable is needed for the receiver; four-core for the transmitter. The required power supply is 11.5 – 14.8v, 25mA for each unit so that cable length should not be a problem.
Before putting the receiver terminal end base cover in place, the alignment evaluation test can be carried out by momentarily shorting terminals at the receiver column PCB and waiting eight seconds to observe the number of LED flashes – according to the manual. The LED also serves as a walk test indicator.
If the Darwin 4 is mounted in an exposed position, then silicone mastic sealing compound will be required to waterproof the base covers.
Performance
We mounted the Darwin 4 on poles with stabilising bases so that the columns could be easily moved in order to assess the limits of misalignment before an alarm was generated.
The results were quite impressive. Carried out at a range of 5.5m between the transmitting and receiving columns, outdoors, either column could be rotated through ten degrees, tilted sideways through 40 degrees or raised through 0.6m before the receiver relay operated.
The alignment evaluation test was carried out after re-aligning the columns, resulting in a single flash – perfect alignment! Unfortunately, the same result was obtained throughout most of the above ranges of misalignment – the number of flashes (one good; four bad) should indicate the quality of alignment. Readings of two or three were obtained only when the misalignment was very close to the limit. So the test is not a critical indicator on the quality of installation. We tried a second sample with the same results which have been conveyed to the manufacturer.
We did try to create false alarms using the usual 55W tungsten halogen car headlamp at close range without response. Also the anti-insect feature worked even when the “insect” settled directly in line with a transmitting or receiving element.
As a result of our experience (limited) with the product, we consider that visual alignment alone, during installation, is quite adequate. The so-called alignment evaluation test is very quick and easy to carry out, as a confidence check. It may prove useful during maintenance visits as an indicator of the level of transmitter power output and receiver sensitivity.
Instructions
The manufacturer’s Installation Manual is written in Italian and translated into English with only a slight loss of idiom in the process.
Installation and fixing instructions are shown in universal picture form, along with adequate brief written explanations.
The manufacturer has promised to attend to the section on alignment which is totally misleading in its present form. Perhaps “signal strength evaluation” would give a more meaningful description of the test.
What the manufacturer says …
Darwin is a miniature infrared beam barrier that can be supplied in 0.5 metre increments, ranging from a 0.5m two-beam model, to a 2m long, eight-beam model. The attractive silver or black anodised aluminium housing comes with simple ‘fix and click’ mounting brackets, making installation quick and easy. It is equally suitable for domestic as well as commercial and industrial applications.
Darwin barriers can be installed indoors with up to 12m range, or outdoors with up to 6m range, typically protecting walls, entrances and window apertures. Each individual beam is optically synchronised with unique identification coding, negating the need for a hard-wired anti-intrusion line synchronisation.
Various software-driven signal processing functions are incorporated. For example, if a single beam is obstructed, an alarm output is generated after two seconds. If two beams are obstructed which are not next to each other (e.g. 1 & 3), the alarm output occurs after one second. Two beams next to each other (e.g. 1 & 2) will general an alarm within 0.1 seconds if simultaneously obstructed.
The unit incorporates a low power alignment option with automatic alignment check to ensure perfect alignment. The Darwin is also equipped with an anti-tamper/removal alarm output.
An anti-insect function is provided to minimise false activations by insects obstructing individual Tx or Rx light heads. When this occurs, the obstructed Tx or Rx unit will look for its diagonally opposite counterpart. If it can ‘see’ the relevant Tx or Rx unit, no alarm will be generated as the target is identified as insect size. (This function is operable only at ranges greater than 1m.) Each Darwin barrier is individually packaged and ready for simple installation and integration within any alarm system.
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