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burglar alarm filters help..

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Wp100

Well-Known Member
Hi,

Have a Honeywell burglar alarm unit thats been running fine for 6 months since installation( by me).

Now for some as yet unkonwn reason one input zone is being triggered by the central heating, though only once every other day or so. ( proven after some timed tests )

Assume some contact on some part of the central heating is causing the fault but it may take some time to isolate exactly what.
Annoyingly, switching the heating on and off manually via its controller many times does not replicate the fault

Until I find the root cause, was looking at tackling the problem is two ways, fitting suppressors to the stats etc and possibly an input filter to the alarm zone input.

Typically on the thermostats contacts a RC main voltage suppressor would be use, but wondered if using and/or a 250v MOV would be better ?

On the alarm zone, which is direct wired to 3 magnetic contacts at 13v dc wondered which would be best, the cable around a ferrite or again a small RC eg 1 M ohm /220nf or even a zener diode ?

thanks
 

Les Jones

Well-Known Member
Most Helpful Member
Are you sure that there are no PIR detectors on the circuit that is failing ? If there are it may be possible that they are being triggered by convection currents from radiators.

Les.
 

Wp100

Well-Known Member
Thanks, but no, only have one PIR and that is on zone 4 and is not in direct line of a radiator; the fault is just on zone 2 with three door mag contacts; the base unit is wireless, my choice.

From noting the time of the false alarms, it has always been when the hot water cylinder is being heated, which is timed to complete before the room heating radiators are switched on (S plan)

No parallel running of the alarm cables along the heating cables though they are within a foot or so at one point.
 

Les Jones

Well-Known Member
Most Helpful Member
I think that the only thing that is different when the hot water is being heated is a motorised valve will be energised. Depending on the design of the heating system there may be on or two motorised valves. It may be a changover (Also called a diverter.) or it could be two simple open and shut valves. one for heating and one for hot water. There will also probably be a thermostat fixed to the hot water cylinder. I would look first at look at putting contact suppressors across the cylinder thermostat contacts and across the contacts that feed the motorised vaves. You may not be able to get at the contacts for the motorised valves so connecing the contact suppressors across the connections to the valves would be an alternative. Are the three door contacts hard wired to the alarm or do they use a wireless link ? These are the sort of contact suppressors I would suggest.

Les.
 
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Wp100

Well-Known Member
Hi,

Ha, was just looking at those suppressor in Farnells /CPC, seems they are the type that have the flying leads , not just the short pcb wires.

I have two valves, both newish ( 1 - 2 years) Honeywell v4043 2 port valves but had not been able to find if they had been fitted with suppressors at the factory, assume not.
The hot water thermostat is about the same age and all are quiet close together along with the heating wiring box so I can fit the suppessors in there with only a short cable run, if I cannot fit them onto the actual valves / stats.

All the door and window contacts and sensors are hard wired, no wireless at all , I'm not a wireless fan.

While I would have hoped the Honeywell alarm unit would have used some form of hardware and software filtering, seems probably not, hence my thoughts about using some form of signal filter on the incoming zone cables, not just for this problem, but to avoid and future noise problems; any sugestiong there ..?

Thanks
 

Les Jones

Well-Known Member
Most Helpful Member
I think it is unlikely that electrical noise is causing the problem. Did you measure the loop resistance of each zone when you installed the system ? If so re measure the resistance of the problem loop and compare the value with the value when it was installed. If it has changed then one of the contacts may have become high resistance. I have also noted the resistance of parts of the larger loops at junction boxes. It makes tracing intermittent faults easier.

Les.
 

Wp100

Well-Known Member
Have not yet started any detailed fault finding, have only been able to establish the times and conditions of the fault as its been very random in that it does not happen each day at the exact same time, but it does only happen when the hot water cylinder heating is on

Will have to work though both systems methodically and see if there is any faulty connection / loop resistance etc, think I will fit those suppressors at the same time as a precuation.

Will let you know what we find, though I'm a slow worker these days ! :)

thanks
 

Wp100

Well-Known Member
Just an update, though all the magnetic contact sensors worked fine when 'walk' tested, it still continued to give an alarm when the hot water heating came on.

Worked though the zone with the dvm which gave erratic resistances and eventually traced a cracked wire in the juction box for the 4 sensors, not where it screws into the pcb connectors but just inside the cable insulation, must have some how damaged it when using the cable strippers.
When I actually gripped that cable to see if it was screwed into the block the wire just came out of the cable sheath.

Thankfully thats the only juction box in the whole system, all other zones 50R or below.

Cheers
 

Les Jones

Well-Known Member
Most Helpful Member
Hi Wp100,
I'm glad that you have found the problem. So it looks like it was just a coincidence yhat it only occurred when the water hering was on. (Unless the junction box was close to some pipes that were only hot when the water was heating.)

Les.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
So. you nicked a wire. Now, you know. Vibration or thermal may have been the cause.

I traced down a intermittent X-10 system to the fan on the furnace. Essentially one of those commutated 3 phase fans (ECM = Electronically Commutated Motor) that run off of 120 VAC.
I didn't measure the noise on the line, but I have a gizmo that could help to do so. I added a filter at the Furnace and problem gone. It also may have "taken out the X-10 system before it was fixed.
 
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