How to Find and Repair Tamper faults in a Hard-wired Slarm system
This article describes the procedures for identifying and rectifying tamper faults in Intruder Alarm Systems. The procedures apply to hard wired systems and in the main to close loop type installations as opposed to EOL wired systems.
Properly installed alarm systems should have all the parts of the system protected by one or more tamper circuits. Each tamper circuit is a single closed loop such that a break in the loop at any point will cause a tamper alarm. The tamper alarm usually signals the internal sounder only when the alarm is unset (Day mode) and a full alarm when the alarm is set.
Typically there are at least four different tamper circuits - a global tamper circuit, control panel tamper, sounder tamper and a Remote Keypad (RKP) tamper.
- Global Tamper - On modern Control Panels there are a pair of terminals on the PCB usually marked TAMP or similar, into which the tamper circuit covering the wiring, detectors, junction boxes and any other devices on the system, are wired. There should be only one wire to each of the two terminals. Note; occasionally there may be single wires going to one of the terminals - these are not part of the tamper loop, they are part of the alarm system for Normally Open detectors (e.g. pressure Mats) where one wire goes to the zone terminals and the other to the tamper circuit.
- Control Panel Tamper - The control panel has a tamper switch which is usually soldered into the PCB, but may occasionally comprise a microswitch wired into the global tamper circuit. Where an RKP (Remote Keypad) is fitted this will also have a tamper circuit which may be wired into the Glbal Tamper circuit or into a dedicated RKP tamper circuit.
- Sounder Tamper - All modern Control Panels have an SAB (Self Actuating Bell) module built into the main control panel PCB. A tamper circuit is part of the SAB. The tamper loop is from the -ve Hold Off through the bell box tamper switch(es) and back to the tamper return. See How to Replace an external sounder for the terminal connections of commonly used control panels.
- RKP Tamper - This tamper circuit can differ between different control panels - some RKPs carry the tamper circuit on the databus from the RKP and others have a separate tamper circuit. For RKPs with a separate tamper circuit this can be linked ourt at the control panel for diagnostic purposes. Where the tamper is carried on the databus this is usually flagged at the control panel as something like 'Rem Tanper' - in this case you will need to ensure that the tamper switch in the RKP is operating correctly.
Finding The Tamper Fault
The first step in finding a tamper fault is to identify which part of the tamper system is at fault. This is done by a process of elimination and because the control panel lid will have to be removed anyway the lid tamper can be quickly eliminated by holding the tamper switch closed and resetting the system. If the system resets, then the lid tamper is at fault. The tamper operating lever/spring can usually be adjusted so that it closes when the lid is fitted. If the tamper fault does not clear, then eliminating the other tamper circuits is made easier if the control panel lid tamper is taped in its closed position.
The other tamper circuits can then be eliminated in turn by fitting a link across the individual tamper terminals and attempting to reset the system. When fitting the links, the existing wiring can be either left in place or removed. With the sounder tamper, the wiring should be left in situ. Note; it is unlikely that there is a fault on more than one tamper circuit, but just in case there is, the links can be left in place until the system can be reset and the circuit at fault noted. The previously fitted links can then be removed one by one checking each time that the panel will reset.
Sounder Tamper Fault
WARNING:The strobe circuit in the sounder unit produces high voltages! Take care not to touch the strobe and its associated circuitry when working on the sounder.. The external sounder (or an internal sounder with an SAB) has one or more microswitches in the bell box which are wired into the tamper loop.
- Remove the bell box cover and Manually close the microswitch(es) and reset the control panel. If the panel resets, then check that the switches are closing correctly when the bell box cover is replaced. The operating arms of the switches can be bent to ensure that they close properly.
- If the panel does not reset with the microswitch(es) closed then the microswitch(es) should be linked out with a short piece of wire.
- If the panel still doesn't reset then the fault is in the cabling. There are two ways to approach this problem - choose the more convenient method. Either;
- Disconnect all the wiring from the sounder, remove the sounder, and rewire it locally at the panel with a short piece of new cable. Or;
- Temporarily rewire the sounder in-situ using new cable.
Global Tamper Fault
Finding the fault again uses the elimination method, however, before opening the panel and disturbing the wiring, make a visual inspection of the system - look for loose wiring, loose covers on junction boxes and detectors etc. If there are no obvious causes of the fault, proceed as follows.
- Disconnect the mains power from the control panel.
- Open the control panel.
- Identify the global tamper terminal on the PCB and the two tamper wires connected to the terminals.
- Trace the wires back from the terminals - they should be connected into a connector strip or other type of connector where all the individual tampers are daisy-chained (serial) to form one continuous loop.
- Dissassemble the wires at the connector strip and identify the tamper pairs from each circuit.
- Test each pair of tamper wires using a continuity tester until the pair at fault is found.
- Once the faulty circuit is found, the cable can be traced back to the detectors/devices along the cable. The tamper circuit can be linked out at various points along its route and tested in order to determine the location of the fault.
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