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Thread: Problem with PIR

  1. #11
    Automated Home Guru neilhooper's Avatar
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    Although I hadn't mentioned it I had tried it on a different input on the same module but not a different module.

    One of my modules with spare inputs is tucked away in another part of the house and nowhere near node 0.

    This is the interesting bit; when I had it connected to the previous module the 12v to the PIR was connected to a separate 12v power supply as are all the PIR's. In the remote location I don't have access to this power supply so I pinched the 12v from the Idranet connector. My wiring sequence was, and this is important to note, to connect the 0v and input connections to the PIR and then the positive and then the negative. After I had connected the positive I dropped the screwdriver and of course it rolled under something. I retrieved my screwdriver and imagine my surprise when I stood up to find the PIR working without the negative connected. I connected it anyway as one should and it worked flawlessly with the voltages dropping from 3.2v to 47mv. I reconnected back to the original module and used the power from that module's Idranet connector and its working perfectly.

    - Neil

  2. #12
    Automated Home Legend Karam's Avatar
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    Hmm, this sounds like the PIR output is not isolated. In other words that the 0V from the digital input is traversing into the 0V for the PIR electronics. Sounds a bit odd not to isolate the output of the PIR since it would suggest that the polarisation of the C and NC terminals is then significant. How have you connected C and NC?

  3. #13
    Automated Home Guru neilhooper's Avatar
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    C > 0v
    NC > Input

  4. #14
    Automated Home Legend Karam's Avatar
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    If you have an unconnected PIR unit perhaps you can take a resistance measurement between the C terminal and the - terminal and see if this reads a low value? If so would imply they are using an unisolated 'open collector' type of arrangement.

  5. #15
    Automated Home Guru neilhooper's Avatar
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    Unpowered:-
    between C and - terminal : OL
    between NC and - terminal : OL

    For Completeness
    Powered but not connected to module:-
    Inactive between C and - terminal 19Mohms
    Active between C and - terminal OL

    When I had it connected did I have it the correct way? I'm presuming that it was because it worked; presumably if it was connected the other way around it wouldn't but I haven't tried it.

  6. #16
    Automated Home Legend Karam's Avatar
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    Ok so I'm scratching my head here. This then doesn't indicate a direct connection between the output and the remainder of the PIR - at least not a straightforward one. Yet some of your previous observations suggest something funny going on. Anyhow as a general guideline if you have any suspicions of connectivity between IDRANet 0V and the 0V of a different supply it is best avoided because 0V is a relative term meaning that noise currents can flow between the 0V connections of the different supplies. In other words better to use the IDRANet supply to provide power to the PIR or smoke detector or whatever if this is possible. Possible meaning that the device can handle up to 15V and that it does not draw too much current. For example the PIR unit consumes about 9mA so quite small relative to the maximum line budget of 1A, whereas if you had a device that consumed 100mA you may have to think more carefully about what else you are powering from that same line. In the case of C and NC labels, though in theory and for a mechanical relay it shouldn't make any difference, I'd go with C to 0V and NC to digital input on the digital input connector.
    Last edited by Karam; 10th February 2014 at 09:04 AM.

  7. #17
    Automated Home Legend chris_j_hunter's Avatar
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    original message mentioned their being several of the new ones - do they all behave the same ?

  8. #18
    Automated Home Legend chris_j_hunter's Avatar
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    another thought - did you try resetting the module ?

  9. #19
    Automated Home Legend Karam's Avatar
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    It would seem that the problem was resolved by supplying the PIR from IDRANet power, but that some of the earlier observations have yet to be explained. For example the issue of the sense voltage only dropping to ~1.2V may have been explainable if an EOL resistance had been selected on the PIR, however the multimeter measurement showed the resistance changing between O.L and ~15ohms. If an EOL resistor were linked in then the latter would more likely be of the order of 2k. Could be that the link position was changed between multimeter resistance measurement and active use voltage sense measurement I suppose. But still leaves the question of how the PIR was seemingly powered with just the '+' terminal connected and later measurements didn't show an obvious path between the '-' terminal and the 0V conection on the output side.

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