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Intruder Alarm Basics

The Major Components

Every Burglar Alarm System comprises at least 3 main components:

Control Panel
Detectors
Signalling devices (usually an external sounder)

Connecting The Components

There are two ways of connecting the components together.

Hard-wired
Wireless (radio)

Hard-wired

The control panel will require a connection to the mains supply and a rechargeable battery for standby.

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)

The basic requirements for connecting contacts to the Control Panel are as follows;

2 Cores for the alarm loop
2 Cores for the tamper loop
2 Cores spare

The basic requirements for connecting remote keypads to the Control Panel are as follows;

2 Cores for data
2 Cores for 12V power
2 Cores spare

The basic requirements for connecting external sounders to the Control Panel are as follows;

1 Core for tamper (usually -ve return)
2 Cores for 12V power
1 Core for sounder activation
1 Core for strobe activation

Wiring is "star" formation - every device requires one 6 core cable between it and the control panel end station

Wireless

Wireless equipment uses radio communications to replace most of the cables of a wired system.

The control panel will require a connection to the mains supply and a rechargeable battery for standby.

External Sounders are usually hard-wired to the Control Panel.

Some wireless systems remote keypads require hard wiring to connect to the control panel end station

The Control Panel

The Control Panel can be considered as the heart of the system. Its main function is to act as an uninterruptible power supply and to control the various functions required. In a nutshell this unit is the brains behind the system allowing you to control the functions such as full set, part (night time) set, unset, reset etc. In addition the unit controls all signalling devices i.e. sounders during setting/unsetting, internal sounders, external sounder/strobes and external communicators signalling via radio or telephone links.

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

Zones 8 fully programmable (CC, 2 wire with global tamper)

Zone Attributes Each zone can be programmed as one of the following types – personal attack, fire,
normal alarm, final exit, 24 hour, entry route, not used, shock analyser (zones 1-4 only),
technical alarm, key-switch (fixed & momentary options) attributes of chime, soak test,
double knock, omit allowed

Panel blank metal end station and LCD keypad packaged as a kit

Keypads Accepts a maximum of four LCD keypads

Proximity Reader An optional plug-on module that turns a Scantronic keypad into a combined keypad and
proximity reader - compatible with a 9930EUR-50 keypad

Display Full feature LCD display with plain text up to 16 characters

Level Setting A = Full Set, B, C & D = Part Set (three part set options)

Event Log 250 event log with date and time stamped

Compliance Currently BS4737

Key switch Key-switch zone, full = A, part = B setting/unsetting, disarm and reset

Codes 16 x 4 digit user access codes, 1 duress code, 1 engineer code

Outputs 3 fully programmable outputs, 13.8v dc +/– 1%dc 1A total current output supply

Battery Stand by battery 7Ah lead acid

System Power Supply Regulated at 1 Amp

Aux DC Power for Detectors 500mA @ 13.7v dc

Programmable zones

Each Zone is a separate 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 it is always best to plan on one zone per device as any false alarms or other problems can be traced without requirement for specialist knowlege. 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 (WT) - also referred to as walk-through. Detectors on a zone programmed as Intermediate will not trigger an alarm within the E/E timed period to allow authorised entry/exit of the property, however with the system set the zone acts as an Immediate zone unless entry to the property is made through the E/E route.
Instant (NA) - detectors on a zone programmed as Immediate will alarm immediately the alarm is set.
Fire (FR) - 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 (TA) - 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.
Keyswitch (KS) - allows a simple key switch to be programmed to operate either part or full set functions.

Codes

Modern alarm systems are unset, set, and programmed via a numeric keypad, either built into the control panel (onboard) or remote (RKP). The alarm is set/unset/part set 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 include a non volatile memory chip (NVM). This is a small memory chip which retains the programmed settings when all power is removed from the Panel, this removes the requirement to reprogram the panel after a power failure.

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). The most commonly used detectors are:

Magnetic Contacts- Fitted to doors and windows)
Passive Infra-red (PIR) devices- (space protection, usually one per vulnerable room/area)
Combined PIR and Microwave devices - usually called Dual Technology device or Dual Tech - (space protection for harsh environments i.e. garages, sheds, conservatories)
Inertia Detectors - also referred to as Shock or Vibration sensors or detectors - perimeter protection, can detect an intruder prior to entry by the vibration caused during a forced entry attempt)
Break glass Detectors - perimeter protection, detects breaking glass, mostly used in shops
Personal Attack devices - manually operated detectors - used to activate an alarm under duress
Smoke/Heat Detectors - designed to activate the system if a fire occurs

Less commonly used detectors include:

Pressure Mats - not now recommended due to high instance of false alarms and maintainance costs
Aluminium foil on glass - only used in high value retail premises
Active Infra-red - only used for warehouses or outdoor space detection systems

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 used to protect large areas of space (typically 10-15m 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 detector generates an alarm output. 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 frequency radio signal is emitted from the detector which is reflected back to the detector at a constant frequency. If this constant alters (e.g. by a door opening or something in the seen area moving) then the detector generates an alarm condition. However for an alarm condition to be generated both the PIR and the Microwave detectors must go open circuit.

Inertia Detectors

These are 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 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 devices in the form of a button with a latch requiring a key to reset. They are basically a switch which is used to generate an alarm when the button or 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, they require to be replaced at 2 - 4 year intervals depending upon traffic.

Aluminium Foil

Comprises a thin strip of aluminium or lead 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 comprise an Infra-red transmitter and a receiver in two separate enclosures, the transmitter sends a beam of focussed infra red light to the receiver which collects the transmission through a lens array, if blocked an alarm condition is generated, often used as dual or quad beam devices requiring both or all four beams to be interrupted simultaneously. They are used in situations requiring a long curtain of protection e.g. inside a factory fence or factory corridor.

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 PCB (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 if either the sounder unit or control panel is removed from the wall during a break in. 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, under extreme conditions the internal battery powers the sounder - self actuating.

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, used by professional installers to report the need for police or other emergency services.