House alarm PIR sensor issue

Discussion in 'Tech Talk' started by Cupoftea, May 28, 2021.

  1. Cupoftea

    Cupoftea New Member

    Dear all,

    We are having a problem with our house alarm, as follows:

    On setting the alarm - Accenta G4, professionally fitted around 8 years ago - (when leaving the house), the main control panel is showing solid red lights on two of the PIR sensors ('as if' they are sensing movement in the rooms where they are located). There is no movement in those rooms. We have also looked at the actual sensors at this point and the red light on the sensors themselves is not 'on' (to indicate the seniors has picked up movement), but the red lights for those sensors on the panel remains solid on. The actual sensors themselves do seem to work as the red lights on them does come on if we move in front of them. I've changed one of the affected PIR sensors, but this hasn't fixed the issue. I've also checked the backup battery in the actual alarm unit and it's showing good (constant 13plus volts). The issue is only resolved if we 'omit' those sensors and leave those rooms unprotected.

    Any input, advice or suggestions from those forum members in the know would be much appreciated.

    Thanks in advance.
     
  2. sparky steve

    sparky steve Screwfix Select

    Have you made any alterations to the programming of the system, or had any work done that may of possibly disturbed the detectors or zones in question?

    Have you performed a system walk test to check the PIRS in question are indeed operating correctly?

    You state the system is 8yrs old, are you still using the original backup battery?


    Where a permanent zone fault is showing and the loop resistance is found to be ok, the most probable cause is a short circuit between the zone wiring and the tamper wiring. When measured with a multimeter the series resistance between the zone and tamper wiring should be infinitely high.
     
  3. Cupoftea

    Cupoftea New Member

    Thanks Sparky Steve,

    No recent work or alterations done.

    Walk through test done. As soon as I enter the test mode the affected PIRs show solid red on the panel ('as if' I was walking in front of them). Incidentally, when they are showing red on the panel they aren't showing red on the actual sensor lights (they do work though, as they do come on when I do actually walk in front of them). The unaffected sensors behave normally in the walk through test (illuminating at the panel one by one as I walk in front of them).

    Yes, original back up battery. Have tested this in isolation (disconnected from the alarm) and it gives a good 13 plus volts, Have been advised to test this under load (connected to the alarm but with the main power to the panel cut off). Suggestions are that at 8 years it will need changing in any case.

    Loop resistance is beyond my level of knowledge, so I'm not sure how I'd check this, nor testing the resistance between the zone and tamper wiring (would I do this at the actual PIR wiring?). Any advice appreciated on the procedure for doing this.

    Thanks again.
     
  4. Cupoftea

    Cupoftea New Member

    Just to add to the above,

    If it's of any relevance, on the sensors there are just 4 wires:
    Black: -0v
    Red: +12v
    Green and Yellow: Alarm

    (No wires to the 'Tamper' connectors on the PIR)
     
  5. sparky steve

    sparky steve Screwfix Select

    Firstly before attempting the following, please ensure you have isolated your alarm control panel from the mains supply.

    Remove the green & yellow (alarm) wires for both zones affected. Now link out both these zones.

    This then effectively removes the alarm wiring from both PIR detectors, which will help determine if the fault is with the panel or indeed the wiring on these 2 zones.


    Now check the operation of your panel. To see if it functions as it should?

    Also i would advise you replace your 8yr old backup battery.

    Regards.
     
  6. Cupoftea

    Cupoftea New Member

    Dear all,

    Many thanks for your various comments and advice on the above.

    Just to update, I've now performed the following tests, with the outlined results.

    1. Changed affected PIR sensor (assuming that was the fault). Didn't fix the problem.
    2. Did a walk through test (see above)
    3. Tested battery away from panel (see above)
    4. Tested battery under load (see above)
    5. Disconnected each of the sensors from the main panel / linked out affected zones (3 and 4) one by one. In each case the panel then behaved normally (i.e. no solid red light for that sensor on the panel when I went to set it).
    6. Connected a short piece of alarm cable to the corresponding sectors on the panel with one of the 'affected' PIR sensors attached) then set the alarm. All normal (i.e. no solid red light on the panel for that sector as above and the sensor on the short cable worked normally / set the alarm off when I walked in front of it (which it hadn't been doing in its original position in the house)).
    7. Did the same for the other affected zone on the panel. Same normal result as above.
    8. Reconnected the original PIR wiring for the affected sensors, went to set the alarm, and the same problem (solid red light for each zone).

    To me as a novice this would indicate some problem with the wiring to each of those sensors. I will change the battery, as I'm not sure if the distance between the panel and the sensor can be affected by this (see the above - the sensors worked ok on a shorter length of cable), but any final input would be appreciated.

    Again, many thanks for all your help.
     
  7. Cupoftea

    Cupoftea New Member

    Just to add to the above, when testing the battery under load the voltage dropped as below (times on left):

    18:00 12.4v disconnected from mains
    18:15 12.36v
    18:40 12.26v
    18:55 12.22v

    Thanks.
     
  8. Cupoftea

    Cupoftea New Member

    Dear all,

    To add to the above:

    ....


    9. Replaced backup battery with new one.

    Problems still there.

    I'd assume this means damaged cables. Just to clarify, two of the four sensors are affected. The original alarm fit was done pre-plastering / flooring completion, so all the wires are now either buried under plaster or finished flooring (so in accessible). Aside from get a completely new wireless alarm system I guess the only way to resolve this is to run fresh cables to each of the affected PIRs. I'll try to hide the cables as much as possible, but I don't see any other way?

    One final thing. I haven't actually looked inside the alarm keypad (next to the front door). This seems a little trickier to open (no screws - juts appear to be 'clipped' shut) and I don't want to break it whilst doing so. Not sure if looking in there would gain anything.

    Thanks again.
     
  9. Rulland

    Rulland Screwfix Select

    It hasn't been 'professionally ' installed then:cool:

    The relays in the pirs can fail, if they fail in the open position the panel will see them as continuously active.
     
  10. Cupoftea

    Cupoftea New Member

    It hasn't been 'professionally ' installed then:cool:

    The relays in the pirs can fail, if they fail in the open position the panel will see them as continuously active.


    Thanks,

    Have changed the 'originally faulty' PIR with a new one and it didn't make any difference (new one did the same as the old one). Then tested this 'originally faulty' PIR on a short piece of cable attached to the panel and it behaved normally. Could the problem still be in the PIR? Do you know how I might test if the relays in the PIRs were in the open position?

    Thanks.
     
  11. Rulland

    Rulland Screwfix Select

    Sounds like a cable issue if the pir works directly connected to the panel, you would have to measure the resistance of the wires to the alarm contact, they should be basically a short circuit or just a few ohms.
     
  12. Cupoftea

    Cupoftea New Member

    Thanks.

    (Sorry - lay person) -


    'you would have to measure the resistance of the wires to the alarm contact'

    So, using a multi-meter at the proper settings, put one probe on the green wire and one on the yellow? Does it make any difference if I do this at the PIR end or the panel end?


    'they should be basically a short circuit or just a few ohms.'

    Is this what they should be if ok, or does this indicate a problem?


    Would I have to power the alarm panel off / remove the battery when doing this?


    Thanks.
     
  13. Rulland

    Rulland Screwfix Select

    Intruder devices are normally closed, so when a pir is NOT sensing movement, you should have just a few ohms resistance at the panel end, if you move in front of the pir, the circuit should go open, infinite resistance.
    There is mains voltage in the panel, just be careful and you should be OK, it's hard to fault find with the pirs powered down as the relays would go open on no power.
     
  14. Cupoftea

    Cupoftea New Member

    Intruder devices are normally closed, so when a pir is NOT sensing movement, you should have just a few ohms resistance at the panel end, if you move in front of the pir, the circuit should go open, infinite resistance.
    There is mains voltage in the panel, just be careful and you should be OK, it's hard to fault find with the pirs powered down as the relays would go open on no power.

    Right, thanks.

    So, if the green/yellow wires are in some way touching somewhere along the wiring (creating a short circuit) then this would create closed circuit? And if this was the case the PIR would not show open at the panel end even if the PIR detected movement? This'd show as minimal resistance.

    But if the relays in the PIRs were in some way open, then the opposite - the panel would assume the PIR had detected movement even if it hadn't? This'd show as inf resistance?

    On this second possibility, I've changed the PIR, so, assuming this replacement PIR isn't faulty, is there any other way a circuit can be 'open' other than in the PIR itself (I can understand how a short circuit in the wiring can create a closed circuit).

    Note: as above, the actual red light on the PIR goes on and off when you walk in front of it but shows as solid red 'detecting movement' on the keypad when you go to set it?

    Thanks again.
     
  15. Rulland

    Rulland Screwfix Select

    Twist the green and yellow together at the pir, measure at the panel, it should be a few ohms, if not you have a cable issue, are there any spare cores nor being used?
     
  16. Cupoftea

    Cupoftea New Member

    Twist the green and yellow together at the pir, measure at the panel, it should be a few ohms, if not you have a cable issue, are there any spare cores nor being used?

    Thanks, will try this.

    No, no spare cores.
     
  17. Cupoftea

    Cupoftea New Member

    Thanks for this.

    Test(s) done.

    Tested each of the zones at the panel (multimeter set to test continuity (200 Ohms)); a) with PIR not set off, b) with PIR set off (walked in front of). Bold are the problematic ones). Power on (12v).

    Zone / reading not set off / reading set off (tested the 'good' PIRs just to make sure working normally showed up as working normally):

    1. 28.7 / 1.
    2. 28.9 / 1.
    3. 1. / 1.
    4. 1. / 1.

    5. 30.8 / 1.

    Then twisted green / yellow wires at PIR end and tested:

    3. 1.
    4. 1.


    So, wires to sensors it is!

    Many thanks for the tips and info.
     
  18. Rulland

    Rulland Screwfix Select

    Yep, looks like a cable issue, you know that the power cores are OK, so you could take readings again, but use either the red or black to the greens and yellows in turn, this would tell you if just one core is broken or both.
    If just one then there is a possible way to bodge a working pir.
    The zone/alarm cores are basically a -ve coming out of the zone terminals and returning to the zone terminals.
    So you could, theoretically loop the -ve in the pir to one side of the alarm contact, and use a good core, yellow or green, to the other side of the alarm contact, and bring this into the relevant return terminal for that zone.
    No guarantees that this will work on your panel, I have done it in the past, depends on the panel, and it would be suck it and see as to which zone terminal it returns on, normally the right hand side one.
    Even more preferable is to run a new cable, but obviously I don't know how easy that would be to achieve.
     
  19. Sparkielev

    Sparkielev Screwfix Select

    Could be a blown fuse inside panel
     
  20. Rulland

    Rulland Screwfix Select

    I don't think that's the case mate, fuses protect wiring that use power, not zone wiring.
    If a fuse had blown for auxiliary devices etc, the pirs would not have visual indication of movement sensed.
     

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