The Major Components

Every Burglar Alarm System comprises at least 3 main components:

• A Control Panel (CP).
• One or more Detectors.
• One or more methods of signalling that an alarm has occurred.

Connecting The Components

There are two ways of connecting the components together.

• Hard-wired
• Wireless (radio)

Hard-wired

Hard wired systems use multi-core cable to connect the various components. The basic requirements for connecting detectors to the Control Panel are as follows;

• 2 Cores for the alarm loop
• 2 Cores for the tamper loop
• 2 cores for 12v power (for powered detectors such as PIRs and Inertia Detectors)

More than one detector can be connected to an alarm loop as long as the loop is kept as a single closed loop.

The tamper loop is also a single closed loop and is daisy chained through all the cabling, and devices on it.

Power to powered detectors must be connected in parallel, i.e. each detector must receive its power directly from the source and not run through other powered detectors.

The external sounder usually requires 5 cores.

Wireless

Wireless equipment operates on specific radio frequencies and each connection comprises a transmitter and reciever. The transmitters are in the detectors and the receiver in (or attached to) the Control Panel. External Sounders are usually hard-wired to the Control Panel.

The Control Panel

The Control Panel can be considered as the heart of the system. Its main function is to act as a simple relay switch (in fact early Control Panels were built using one or more relays) to switch the signalling on when a signal from a detector changed state i.e changed from closed circuit (NC) to open circuit (OC) or vice versa.. Modern Control Panels use integrated circuits to do the switching. Modern Control Panels now have a multitude of programmable features, the most common are eplained below.

If you look at a typical feature list of a professional quality Control Panel, you may see something like the following:

• 8 Fully Programmable zones plus Tamper
• 4 Codes
• Accepts up to 6 remote keypads
• Chime facility
• Part set facility
• Non-volatile Memory (NVM)

Programmable zones

Each Zone is a seperate detection circuit. A Zone (if enabled) can have one or more detectors connected to it. Most types of detector connected to Control Panels are Normally Closed (NC) devices and as such are connected to each other in series such that if any of the detectors on the circuit goes Open Circuit (NO) the zone that the circuit is connected to signals the Control Panel. How the Control Panel reacts to that signal depends on how that Zone is programmed.

Zones can usually be programmed to one of the following types.

• Entry/exit (E/E) - detectors connected to a zone programmed as E/E will not cause an alarm if they are triggered within a user-defined time, thus allowing entry to and exit from the property within the pre-set time. If the entry time expires before the alarm is unset or the exit time expires before all the detectors on the E/E circuit are cleared, the alarm will be triggered.

• Intermediate - also referred to as inhibited. Detectors on a zone programmed as Internediate will not trigger an alarm within the E/E timed period on exiting the property, however the zone then acts as an Immediate zone unless entry to the property is made through the E/E route.

• Immediate - detectors on a zone programmed as Immediate will alarm immediately the alarm is set.

• Fire - detectors (smoke or heat detectors or a manual fire point) on a zone set to Fire will trigger a full alarm whether the actual burglar alarm is set or not. On some control panels the Sounder pulses differently to indicate that it is a detector on the Fire zone that has caused the alarm. Some control Panels have a zone which is pre-set as a Fire zone.

• Personal Attack (PA) - detectors (usually personal attack buttons or pushes) will cause a full alarm whether the alarm is set or not. Some control Panels have a zone which is pre-set as a PA zone.

• Tamper - this zone does not have any detectors connected to it. It is simply a closed loop which runs through all the detectors, sounders, and the cabling such that if the alarm is tampered with (e.g. the cover of a PIR removed or a wire cut) it will cause an alarm. If the alarm is unset, only the internal sounders will sound. If the alarm is set then a full alarm is sounded.

Codes

Most modern alarm systems are unset, set, and programmed via a keyboard (either on-board or remote (RKP)). The alarm is set/unset by entering a user-defined code (usually 4 digits). Some control panels can be programmed to accept more than one code with the different codes having different access areas or the ability to only programme certain functions.

Remote Keypads (RKPs)

Most Control Panels have the facility to connect extra RKPs. These exactly mirror the functions of the on-board keypad (if fitted).

Chime

The Chime facility allows one or more zones to be set to Chime, which then causes detectors on that zone to sound the low volume internal sounder whenever the detector(s) are triggered.

Part Set

Most Control Panels have a Part Set facility (some have multiple Part Sets). This allows a pre-programmed number of zones to be set.

Non-volatile Memory (NVM)

All professional quality Control Panels have an NVM. This is a small memory chip which retains the programmed settings when all power is removed from the Panel.

Detectors

There are several types of detector currently available. They can be physically connected (hard-wired) to the Control Panel or, for some types of detector, via a radio link (wireless or wirefree). The most commonly used detectors are:

• Magnetic Contacts
• Passive Infra-red (PIR) devices
• Combined PIR and Microwave devices - usually called Dual Technology device or Dual Techs.
• Inertia Detectors - also referred to as Shock or Vibration sensors or detectors.
• Breakglass Detectors.
• Peronal Attack devices - manually operated detectors.

Other less commonly used detectors include:

• Pressure Mats.
• Aluminium foil on glass
• Active Infra-red

Magnetic Contacts

Magnetic contacts are used on doors and windows. They are a Normally Closed (NC) detector and comprise two parts - a reed switch and a magnet. The reed switch is closed when in close proximity to the magnet. The magnet is fitted to the door or window and the switch to the door or window frame such that when the door or window is closed the two parts are adjacent and the switch is closed.

Passive Infra-red (PIR) Detectors

Also referred to as space or motion detectors. They are NC devices used to protect large areas of space (typically 15m range x 90°). They work by detecting heat (infra-red) emitted by objects within their range. The detector is covered by a lens which partitions the seen area into several zones. Their internal processor monitors the temperature of the zones and if any of the zones sees a temperature rise or fall the circuit goes Open Circuit. The rate of temperature rise or fall is pre-set to certain limits such that, for example,a central heating radiator will not create an alarm condition.

Pet Immune versions of PIR are available. These are generally simply less sensitive although some are only less sensitive below a certain height.

Combined PIR and Microwave Detectors (Dual Tech)

These are similar to PIRs but have a Microwave Detector fitted in the same enclosure. The microwave detector sees space (volume). A microwave beam is emitted from the detector which is reflected back to the detector at a constant value. If this constant alters (e.g. by a door opening or something in the seen area moving) then the detector goes Open Circuit. However for an alarm condition to be generated both the PIR and the Microwave detectors must go open circuit.

Inertia Detectors

These are NC detectors usually fitted to door and window frames. They contain an internal processor which is tuned to detect the frequencies generated by someone attempting to break in through the door or window. They can also be used on walls.

Breakglass Detectors

These are NC devices used to protect large areas of glass (typical detection range is ~ 7 metres radius). They work by detecting the sound of breaking glass through one or more microphones. They contain an internal processor which is tuned to detect the frequencies generated by the sound of breaking glass.

Personal Attack Devices

These are NC devices in the form of a button or push. They are basically a magnetic contact in which the magnet is moved away from the switch when the button or push is operated.

Pressure Mats

These are Normally Open Devices and are usually fitted under carpets such that an intruder walking on them causes them to go closed circuit.

Aluminium Foil

This comprises a thin strip of aluminium foil stuck to a surface (usually glass) in the form of a closed loop such that if the glass is broken or removed the circuit is broken.

Active Infra-red Detectors

These are NC devices and comprise an Infra-red transmitter and a receiver. They are used in situations requiring a long curtain of protection e.g. inside a factory fence.

Signalling Devices

The most commonly used Signalling Device is the External and/or Internal Sounder, usually combined with a flashing Strobe light. Other Signalling Devices include:

• Speech Diallers
• Digital Communicators

Sounders

Sounders are the most common method of signalling an alarm. Modern day external sounders are self-contained units and incorporate a Self Actuating Bell (SAB) module. The SAB module contains a small battery and associated charging and control circuitry. The SAB causes the sounder to operate if the cable to it is cut or it is removed from the wall. In non-alarm state the sounder draws a little power from the Control Panel for the battery recharge and the status LED(s). Under alarm conditions the sounder is powered from the Control Panel.

Speech Diallers

Speech Diallers are add-on units that when triggered by an alarm will dial 3 or 4 telephone numbers and deliver a pre-recorded message.

Digital Communicators

These add-on units allow the alarm to send digitised information to a Central Station monitoring facility.