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2.
If faults are still present then split the IDIS loop into three or four smaller
sections. Try each section in turn, reinitialising each time. (Allow for
missing zones). See if you can isolate the faults to one section of the
loop. If a section cannot be driven alone from the panel because of its
physical location then use the Handheld Programmer with a local power
supply to test that section.
3.
Once you have found a faulty section of the loop then check the current
readings of each module (see Table 4). Try isolating n-wire modules
from their contacts and sensors (link the tamper and alarm loops as
though the contacts are closed). If this fixes the problem then look for
ground faults in the contact wiring.
4.
If you still cannot find a specific fault then break the loop into smaller
sections and repeat the checking.
5.
Once you have all sections of the loop working correctly as individual
sections then reconnect all of them to the panel and reinitialise. If the
complete loop still does not work properly then the fault is most likely
due to capacitance loading or ground fault.
6.
Isolate the whole loop from the panel and check for connection between
the loop 0V wire and ground. There should be no connection.
7.
Split the loop into two approximately equal sections, with at least some
sensors in each section. Connect one section at a time and reinitialise.
If the system works with either section but not both it has a capacitance
loading problem.
Improving the Voltage Drop
You can improve the voltage drop by: thickening the 0V wire, reducing the
current drawn by different sensors, or adding remote power supplies.
Use thicker cable for the 0V wire.
Standard alarm cable has a resistance of
the order of 10 Ohms per 100 metres per core. For example: five typical relay
PIRs, each drawing 25mA, connected to the end of a 100 metre length of
cable produce a voltage drop along the 0V wire of approximately 1.2V.
Doubling up the 0V wire reduces the drop to 0.6V - a more acceptable level.
You can thicken the cable selectively. Six PIRs at the end of 50 metres of
cable causes more voltage drop than one PIR at the end of 100 metres.
Taking care during system layout can prevent such problems arising.
Reducing current consumption.
At all costs avoid intermittent heavy loads
such as sounders taking their supply via the IDIS 0V wires.
Fitting a PSU
Local PSU(s) can be added at intermediate points of an IDIS loop. The +ve
feed from the panel can be totally disconnected from the IDIS bus or used to
power a few more local sensors with the remote PSU powering the rest. See
Figure 14.
8136
Fitting a PSU
Summary of Contents for 8136UK-50
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