MP500/4N-8-16 Installation
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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 rec eiver.
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 signal s 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: elec tric 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.
3.3.8 Tips about the mobile phone network (GSM)
The information found in paragraph
3.3.7 Tips about installing the radio devices
is also valid for the mobile phone network signal.
The main difference consists in the fact that, in place of the internal antenna of the GSM interface, an external antenna pos itioned in
the best signal reception point can be used.
During the site survey, in order to identify the best place to install the control panel or the antenna, the quality of the mobile phone
network may be empirically verified by observing the level of the signal as indicated on a cell phone. In order to carry out the test, it is
important to use a SIM Card of the telephone service provider to be used, in order to prevent false indications.
