DS1067-063D
40
LBT20064
3.3.6.6
Positioning the supplementary power supplies
Any supplementary power supplies must be positioned:
As near as possible to the devices to be powered to minimise a loss of voltage caused by the length of the wires.
Inside the distribution cabinet or a similar container, adequately protected by anti-tamper devices. The use of an
unsuitable container may invalidate the certification of the grade of security of the system.
3.3.7
Tips about installing the radio devices
The maximum connection distance between two radio apparatus is determined by the intensity of the signal that reaches
the receiver. This intensity, or strength, is determined by the power of the transmitter, by the effectiveness of the
antenna, and by the losses due to resistance, one of which is linked to the distance between the apparatus. In fact, it
must be remember that in a free field with no obstacles, the power of the radio signal decreases any way with the
squaring of the distance. In other words, by doubling the distance, the power is reduced by one quarter and so on.
Besides power, the antenna, and the distance, the two factors that influence the strength of the signal are absorption
phenomena and reflection of the radio waves. Absorption can be considered a loss of signal power when it must travel
through some materials. In this case, the higher the refractive index, the greater the absorption. In the table below are
the groups of some of the most common materials divided by their refractive index.
Low refractive index
Middle refractive index
High refractive index
Wood (ex. armoires, furniture), plastic,
synthetic materials (ex. Plexiglas),
glass, hollow bricks (ex. interior walls).
Water (ex. aquariums), solid brick,
marble.
Concrete, bullet-proof glass, metallic
structures
(desks,
concrete
reinforcement
structures,
electrical
appliances, pipes, gates)
Reflection phenomena influence the signal in two ways. The first is the directivity granted to the signal from the
"reflecting" surfaces, like sheet metal or mirrors, located near the radio device and that reflect many of the radio waves
that strike it. The second is the phase shift of the radio signals that reach the receiver after having travelled paths that are
not "optical". The sum of the signals with phase shifts may be subject to a loss of power of the radio signal received.
In some cases, the signal may even be practically cancelled. For example, a cupboard made completely in metal shields
all the radio signals, which can neither enter or exit it.
Another phenomenon can obstruct radio communications: electromagnetic disturbances. In this case the signal from the
radio devices, even if sufficiently powerful, may be covered and made incomprehensible, thereby obstructing
communications. The phenomenon is similar to that of trying to talk normally in a very noisy room: once in a while, one
word might get through, but the sense of the conversation is lost.
Different electrical and electronic devices may create electromagnetic disturbances if they are not adequately shielded:
electric motors, electric control panels, computers, fluorescent light bulbs, etc.
Given that even the intensity of the disturbance lessens with the square of the distance, many times it is sufficient to
move away from the source of the disturbance to solve the problem.
For a correct installation of the radio devices, take the following precautions:
Install the control panel in the best possible barycentric position in relation to other radio devices.
Position the devices far from electromagnetic disturbances.
Do not install devices on metal surfaces or near large metal objects, or inside metallic structures.
Summary of Contents for 1067/024
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