MP500/4N-8-16 Installation
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2.3.2.6
Passive infra-red detector (IR)
This detector is equipped with one or more IR sensors that measure the rapid variations of infra-red traces of the environment being
controlled, indicating the presence of human beings, animals, or other "warm" objects that move. A variation of this type generates a
signalling by the detector. The effectiveness of the detector and the area covered are changed by adjusting its sensitivity, changing the
Fresnel lenses that focus on the sensor the controlled area or by suitably masking the sensor itself. Some detectors make it possible to
create a curtain covering, or to monitor a very long and narrow vertical area, typically positioned parallel and not far from a group or
windows or doors (hence its name). In the intrusion alarm system, these detectors are used to control extensive spaces and obligatory
passages, also being identified as volumetric sensors.
2.3.2.7
Active infra-red detectors
This IR detector consists of two elements that face each other and are aligned to create an infra-red ray barrier. When an object
passes through the passage controlled by the detector, the rays are interrupted and the IR sensor generates a signal. Technically, the
detector can be created in two different ways. In the first way, the two elements contain one sensor and the other light sources that
emit a ray of infra-red light. In the other, an element contains both the sensor and the infra-red light source and the other element
consists of a mirror that reflects the IR light towards the sensor.
2.3.2.8
Microwave detector (MW)
This detector acts like a radar: it emits a radio signal and then detects and analyses the return signal (reflected waves). When the
return signal varies, due to something that has moved in the area covered by the detector, a signal is generated by the detec tor. Unlike
the passive IR detector, the movement are detected even if the person moving emits or blocks heat. In the intrusion alarm system,
these detector are used to control extensive spaces and obligatory passages, also being identified as volumetric sensors.
2.3.2.9
Combined passive IR and microwave detector
This type of detector combines both technologies. The signals generated by the sensors can be compared to OR or AND logic. In the
first case it is sufficient for just one sensor to detect an anomaly for the detector to send a signal; in the second case, both sensors
must detect an anomaly for a signal to be sent. The two settings have a mirror effect. With OR, the possibility of identifying attempts to
intrude increase (what one sensor detects, the other sensor might not), together with and increase in the generation of false alarms.
With AND, the possibility of generating false alarms decreases (the sensors must essentially confirm each other), but the sensitivity in
detecting attempted intrusions also decreases.
2.3.2.10
External detectors
The external detectors are essentially a specialisation of some of the types of detectors already illustrated herein.
An external detector has a more resistant protective casing that enables it to resist the elements as well as attempted sabotage. Even
the sensors used can have higher performance scores, but the operational principles are the same.
2.3.3 The signalling devices
This category includes all the devices capable of notifying people and other systems or equipment of a dangerous situation for people
or property placed under the protection of the intrusion alarm system.
2.3.3.1
Siren
The siren is a device that emits a very powerful sound that can easily be heard at a distance to warn of an attempted intrusion. External
sirens must have a power of at least 100 dB, while internal sirens must have a power of at least 80 dB at 1 metre; if the s ound is less
powerful than these standards, the device is simply an acoustic signal. The siren is a mandatory element. The minimum and maximum
duration of the acoustic signal is established by law and by national and local regulations and provisions. In addition to the external
siren, the alarm systems must also have an internal acoustic warning device. This warning device need not necessarily be a se parate
component, but may be a function performed by some other device, like the control panel.
2.3.3.2
Flasher
The flasher is a visual warning usually combined with the external siren. The flasher signals a message through codified sequence s of
lights and is visible at a great distance. In addition to signalling an attempted intrusion, based on the capacity of the con trol panel the
flasher can provide further information, like the visual confirmation of the system arming and disarming from the external, the presence
of alarms saved, etc.
2.3.3.3
Communicator
The communicator is an interface, sometimes also called the auto-dialler, which enables the system to send alarm signals or other
signals at a distance and, if configured to do so, receive commands from remote. There are two types of devices: the one to connect to
the traditional telephone network (PSTN) and the one to connect to the mobile phone network (GSM and later). The two interfaces can
co-exist in the same system, where each one constitutes the back-up of the other. These interfaces are usually hosted inside the
control panel, but they can also be an independent device, physically separated from it.
The signals sent from a communicator can be either vocal or SMS (towards telephone numbers) or in numeric format (for an alarm
reception centre). The commands can be received from the control panel in the form of DTMF signals or SMS, or in numerical format.
What can be obtained by using a communicator depends on the network and on the channel of communication used, as well as the
functions the control panel can carry out.
The level of detail of the signals received may vary considerably and depend on the control panel, on the channel of communication
used, and on the auto-dialler. It may range from a simple vocal message like "Intrusion alarm in ....street" to a signal that includes the
indication of which detector signalled the alarm, the time it occurred, and so forth.
