The Control Box
THE BASIC ALARM CONTROL UNIT - The Technical Side
The Control Box (also known as a CU) Is the heart of an Intruder Alarm) It either has an integral KEYPAD, or is fitted with a REMOTE KEPAD to allow the main box to be fitted in a better position for a mains power supply and to run cables out to the detection and signalling devices, but still leaving the KEY PAD, or in this case the Remote Key pad RKP in a convenient place for alarm setting and unsetting.
Each detection device needing a source of power to run it, typically a PIR, should be on a separate zone or circuit. The zone is usually labelled c/c loop, zone 1,2,3 etc.or similar. There may also be a TAMPER zone for each zone
The + and - are the 12 volt supply to the detector(usually a PIR). The c/c (closed circuit) loop is the part that creates an alarm condition. When the alarm is set this loop is closed circuit, hence c/c loop. And when the PIR. door contact etc. is opened or goes into an alarm condition, the loop is broken(goes open circuit) thus setting off the alarm. Apart from making a lot of noise, the control unit will indicate what zone or circuit has operated via an LCD (liquid crystal) or LED (light emitting diode) display, or in some cases, in older systems, a panel light marked with the appropriate zone.
CLOSED CIRCUIT LOOP
A CC (closed circuit) loop operates totally opposite to a torch switch or bell push. A bell push or torch switch is an OC (open circuit) device. That means that in normal (off) circumstances no connections made between the two ends. When the bell switch is pushed, or the torch is turned on, the connection is completed, thus sounding the bell or lighting the torch.
This principal is simple but has a major flaw. If the connections between the switch and the bell or bulb is cut or broken, the unit will appear OK, but will not work when the switch is operated, as a circuit will not be completed-you will not know the torch is faulty until you need it!
This would be a minor inconvenience for a front door bell or torch, but could have serious consequences for a security alarm.
The closed circuit system used in almost every alarm installation means that if the connection on the detector circuit is damaged or faulty, the alarm will trigger, or if not set, the zone will not be clear when an attempt is made to set the alarm system.The CC (closed circuit loop)will not operate the alarm until the system is SET (ARMED) This is another good reason for having each detector on an individual zone or circuit. Fault finding is much simpler!
TAMPER ZONE
As an added safeguard, most control units have an additional closed circuit zone known as a TAMPER. This is similar to the C/C loop. Tamper loops except that the TAMPER loop must be closed (connected) whether the alarm is set or unset. If the loop is broken at any point the alarm will sound, usually internally only, if the system is not set, when they are broken. On most control boxes, the tamper circuit may give separate indications of its positione.e.g tamper zone 3 is the tamper zone on the cabling and detector unit fixed to zone 3.
The tamper loop is to indicate a cut cable or tampering with detection devices 24 hours per day. PIR’S have 6 connections. + for 12volt positive connection, - for 12 volt negative connection, C/C loop {closed circuit} (PAIR), for the alarm operating connection and S/P (single pole) loop (PAIR) or tamper, for tamper protection. These are connected back in the main alarm control unit in the appropriate positions. If the lid or cover is removed from the PIR, even when the alarm is not set, a tamper alarm is sounded, and an appropriate indicator is operated on the main control unit. The same alarm condition will be triggered if the connecting cable to the PIR is cut.
To silence the tamper alarm, the user set/ unset code has to be entered on the alarm control unit. On older key operated control boxes the key switch usually has a tamper silence position.
CONTACTS or SWITCHES are fed by a 4 core cable. One pair of cables forms the C/C (closed circuit) loop connected across the contact. When the switch is operated by the door etc. being opened, the zone or circuit goes into an alarm condition. The second pair of cables are connected in the contact in the form of a loop and is connected back to the circuit tamper. When a problem is found on a zone the fault can be isolated by connecting the two loop connections with a loop of wire in the alarm control unit (if end of circuit resistors are used, one should be used to loop out the connection)within the control unit. If the zone is then clear, on the control panel, the fault is on the external zone or circuit, and the control unit is OK. Make sure that only like poles are linked together, as a connection between a + and- could damage the control unit. Use a long piece of wire as a temporary loop, and let it trail out of the control box. This should make it difficult to accidentally leave a circuit or zone disconnected.
Do not run alarm cables parallel to mains cables as mains spikes may be induced into the alarm cable and cause a false alarm.This is most important when the mains supply cables are powering fluorescent lights,fridges, freezers and electric motors.
24 HOUR ZONE OR CIRCUIT
A 24-hour zone is a facility that may be programmed into some alarm control units. If they are used for foil, CC WIRING etc., they will sound the alarm as soon as they are broken, to allow repairs to be made before the system needs to be set. When the system is set, they operate exactly the same way as other night zones or circuits.
A 24-hour zone may also be used on stockroomsetc. needing a level of protection during alarm unset periods. The advantage of using a 24 hour zone instead of using a tamper zone, is that a 24 hour zone may be ISOLATEd (turned off) from the alarm control panel to allow access.
EXIT ROUTE (ACCESS)
The exit route circuit is usually the final door that is shut when leaving your premises and any detection devices that are triggered between the final exit door and the KEYPAD
In most modern control units the exit route can be any circuit or zone, and is programmed in at the time of installation.
The exit route circuit is operated by at timer device, set to around 20 to 60 seconds, to allow the operator to pass through the exit zone protection and leave the premises before the alarm sets fully.
Once the exit setting sounder has stopped, when the last door is shut, the alarm is fully set. The exit zone will not cause an alarm condition as soon as it is triggered, but it will start the entry exit timer, sounding the exit sounder. If the correct code is not entered into the alarm control box within the pre set entry exit time, the full alarm will sound
Because of this, it is good practice to keep the amount of detection on the exit circuit to a minimum. On police calling systems DD243 specifies special conditions for exit rout circuits.
More than one EXIT ROUTE may be programmed on a modern control unit.
EXTERNAL SOUNDERS (CLOSED CIRCUIT)
Also known as OBA, SAB (outside bell apparatus-self actuating bell) A dummy external sounder box is also often fitted on the rear of the premises.
A basic alarm system just operates a loud warning inside, the premises, to frighten off intruders, and an external sounder to alert neighbours and passers by. The external alarm box is sometimes fitted with a light. This shows that it is not a dummy box, and is often fitted with a flashing strobe light which can be programmed to flash after the sounder has stopped, or to stop when the sounder is stopped by the timer, if fitted.
The duration of the sounder should be limited to 20 minutes, to ensure good relations with neighbours and to prevent falling foul of noise legislation. Most internal sounders continue sounding until the system is turned off.
External sounders vary from a simple bell-operating on the same principle as a door bell OC BELL (open circuit), to an electronic, closed circuit or self actuating sounder, fitted with its own float-charged battery supply. Most modern sounders are of a self-contained type, with a built-in cut-off timer. Older sounders rely on a supply from the main control unit to stop them operating from their own integral float charged battery supply, and are not fitted with their own cut out timer. If the supply is removed, they may sound for many hours!
The best advice is, if you cannot stop your alarm sounding DO NOT TURN OFF THE MAINS SUPPLY, OR PULL OUT THE EXTERNAL SOUNDER WIRES. Either action will ensure that the sounder does not stop!
Although it is a worry to many people, it is very rare for an outside sounder to be attacked on a normal house, not containing antiques or high value items.
With a suitable relay a mains operated siren can be used on a standard control unit sounder output, using the O/C (open circuit) bell output to operate a mains operated relay. Do not attempt this unless you are confident that all electrical safety precautions have been taken. If in doubt or if it is a legal requirement - USE A QUALIFIED ELECTRICIAN.
The siren is still an O/C device, and is therefore vulnerable to attack. This means that a voltage has to be applied to the siren to make it sound. Therefore if the cable from the control unit to siren is cut or damaged the siren will not sound.
With thanks to Tony Render, Managing Director and Dave Almond, Service Director of RENDER ALARMS Middlesbrough 01642 230696, For the equipment illustrations and support.