PIRs on FSL wiring

[Guest anpick]

Dear colleagues

I have just completed a domestic installation of a Scantronic 9751 alarm system using Fully Supervised Loop (FSL) wiring. I have 8 zones and had to connect some sensors in series (max 2). I know that this may make identification of trigger sensors difficult but the layout is logical and where a pair exists they are physically close.

Configuration causing the problem: 2 PIRS wired in series with 4.7K across each contact, 2.2k EOL and return to the control panel via each tamper contact wired in series in the same loop.

Problem is (for 2 PIRs connected in series), using the recommended 2.2k EOL resistor with 4.7k resistors across each of the 2 alarm contact the 9751 will trigger a tamper alarm if both alarm contacts are open (even when the system is not set since tamper detection is always 24hrs). When both PIRs are triggered the series resistance is 2.2k + 4.7k + 4.7k which the 9751 believes to be near enough an open circuit (hence regarded as a tamper).

I find it hard to believe that FSL cannot support series detectors!

The only logical solution would be to wire [a single 4.7k resistor] in parallel with [all alarm contacts connected in series]. Thus, when any of the alarm contacts open the single 4.7k resistor is switched in.

None of the documentation that I have for either the control panel or the array of sensors/detectors provides any useful guidance. The assumption seems to be one detector = one zone.

Help would be appreciated.

Andrew

[Guest anpick]

Pete,

Thanks for your prompt response.

I have additional cables already installed in this case (i.e. radial from control panel). I have slightly more detectors than zones but in this case I have two PIRs that I wish to allocate to the same zone and each has a dedicated 6 core cable from the control panel.

So, physically I have dedicated wiring for each of the two PIRs. Electrically, though I wish to connect to one zone using FSL. So, at the control panel I have full flexibility to connect the PIRs in any way I choose.

So, should I connect a single 2.2k resistor across [the two alarm contacts connected in series]...? Is this how FSL was intended to work?

The more expensive solution would be to use an expander if the 'industry rule' is one detector per zone.

Andrew

[Guest Adrian]

B) Unless you are using latching sensors, no forget it get an exspander they are not that exspensive.and the job will be done right the 1st time. Just think you will have the extra zones available for when they build the extention.

You know the story you filled the panel (zones) been paid walked away, then they say "I,ve been thinking can I have a panic button in the bedroom, and that sensor in the garage we talked about"(12 months ago)

Adrian B)

[Guest jem]

you can wire more than one sensor in series to a fsl, but not PIR'S. You can have upto 10 reed switches on a circuit by BS4737. On most fsl systems you would need to run a third wire or core between sensor. If you want a pic I will send you one.