Random PA alarm

[ComfortGeek]

Hopefully someone can help!

I have 3 PA buttons wired with end of line resistors on one circuit.  All works fine.  You press the PA\'s, they go off as expected.  You try take the cover off, the tamper alarm goes off as expected.

But then at random, the PA alarm just goes off on it\'s own!

I don\'t think it\'s the wiring as they normally work ok, I don\'t think it\'s a problem with the resistors for the same reason, the EOL setting for the zone is correct - so what could it be?

Coudl it simply by the reed switch in one of the PAs is dodgy and is opening the circuit perhaps as temperature changes?  Could the 60 metres of wire be reducing the resistance?

Or am I being dumb and have missed something more fundametal?

[slychiu]

There should be 1 set of EOL resistors in the circuit and not for each contact

There may be resistance issues. Measure the voltage when the switches are open and Closed. The voltage will show how close to the threshold the open and close states are

It could also be a fault or intermittent switch

[ComfortGeek]

Thanks

I can confirm that only one set of EOL resistors (two resistors, 1 x 4.7k, 1 x 2.7k) is being used across the 3 PA contacts, as per the installation manual and as supplied with the comfort PCB.

I have changed the PA button I thought might be faulty, but the random alarm occured again at 3am! So this did not sort it.

Next I\'ll try measuring the voltage to see if resistance is an issue- can you let me know what I should be looking for?  i.e. what is right and what is wrong?  Do I measure at the comfort zone terminals or remotely at each PA?

Only other thing I can think of is 20cm of the alarm cable to one of the PAs runs along side a 240v lighting cable - I have no choice.  I have used screened 8 core wire, so didn\'t think this would be a problem for a PA circuit?  Could this be it?

Finally, just for info, all three PA\'s are wired back to the CPU where I have used a terminal block to connect the wires - so it is wired correctly, the wires simply all come back to the CPU rather than being a daisy chain.  This makes the wires longer but cannot see how this could effect anything other than circuit resistance?

So, in summary, the issue could be due to either:

- a Fault on comfort PCB for that zonet - if so, how resolve?

- Wire being along side 240v cable - if so, how resolve?

- faulty resistors - I\'ll change them to rule this out

- circuit cable length too long - if so, not sure what to do as I don\'t want to use 3 zones for the PA circuits....

If I\'ve missed any, would be good to get your view.

[Vangelis]

A couple of thoughts...

Could try wiring the PA buttons into the Comfort \'case tamper\' cct (not very eloquent I know) but will rule out a faulty onboard issue (guess you will need to remove the EOLs)

If you have spare Zones then wire the PA\'s into their individual zone - this will rule out the shielded cable running via the lighting cct and faulty unit and identify a failing units.

You could sacrifice another Zone temporarily to do this - especially if its going off at 3am!!!

[ident]

closed 1.12V
open 1.87V

measured at terminal block

[ComfortGeek]

Thanks - All good ideas, will give it all a go!

Would still be good to know what I should be looking for in terms of measuring the voltage / resistence in the circuit...

Thanks again - it\'s driving me (and the household) bonkers!

[cleaner]

Set longer sensitivity of the zone type eg to 1 second so that short pulse do not trigger the alarm

[ComfortGeek]

Ok - I have measured the circuit at the terminal block

When closed, it is 1.17v
When open, it is 1.9v

So, what does that mean? Comparing it to the numbers you said, sounds like it\'s right?

So, if it keeps false alarming and the circuit voltage is ok, what could it be?

Can a resistor be ok one minute then faulty the next?

or

could the voltage be effected becuase the alarm cable runs alongside a 240v cable for about 10cm?

or

Can comfort PCB for that zone intermitemtly be faulty?

Please help, it\'s driving me mad!

I\'m thinking the only answer will be to do away with the resistors and just have a normal circuit and wire the tamper contacts in series with the alarm contacts - then the PA will go off if anyone tries to tamper with it

[ident]

The voltages are correct which means that the resistors and wire resistance is not the problem
The 240V wires running close to the zone wires may be a problem

Have you increased the zone sensitivity to  1 second as suggested below
What zone sensitivity is being used now?

It is highly unlikely the Comfort Input is fault. To check, connect a short circuit with EOL resistors at the Inputs and see if there are any more false alarms.

[ComfortGeek]

Thanks

Really stupid question. Sensitivity is currently 500. The drop down box to change the sensitivity goes up to 850 ms but can\'t see option for 1second.

So question is, how do I change sensitivity to one second?