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Thread: Where to locate combined temp & PIR?

  1. #1
    Automated Home Guru jpdw's Avatar
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    Oct 2007

    Question Where to locate combined temp & PIR?

    Planning for my new kitchen has got me wondering this question ... (plus it enables me to start the first thread on the shiny new Idratek forum )

    Conventional wisdom suggests
    - thermostats etc work well when postioned arouns shoulder height
    - PIRs tend to do best when in/on the ceiling

    But if I want to use a combined PIR/DTS in my kitchen, where's the best place to mount it ... I mean, on the ceiling wont it always read too high, whilst on the wall will it "miss" spotting presence (and therefore switching the lights out) ?

    What works best in practice?

  2. #2
    Automated Home Legend Karam's Avatar
    Join Date
    Mar 2005


    Shoulder height is good. If the unit is placed on a wall adjacent to a doorway it will pick up entry motion very quickly and so light switching ON operations for example will be quick. Once the room has been entered, the occupancy assessment algorithms will ensure that even if no motion is subsequently detected for a long time the room will still be deemed to be occupied, unless the occupant leaves to another room, so the light would stay ON until then. You have to remember that the IDRATEK system uses occupancy state to control functions rather than simply motion detect + timer, so in a sense its better to quickly and cleanly detect entry to a room than it is to continuously monitor motion.

    Having said this it does help to get occasional re-affirmation so if the PTS is placed well for quick entry detection but not at all well for general in room detection then a second PIR unit (can even be off the shelf type connected to a convenient IDRATEK digital input) may be installed to give better/augmented room coverage - for example in a top corner of a rectangular room.



  3. #3
    Automated Home Legend Paul_B's Avatar
    Join Date
    Jul 2006
    Eastbourne, UK


    It gets more difficult with multiple sensors in a single module. It may not always be the best way to go.

    Also consider the following scenario where a room is located next to another via a door. You don't want the PIR picking up movement through an open door. So in my case I mounted a PIR above the door frame which works great for entry and exit but not so great in an L-shaped room where detection may get missed around the blind corner.

    One thing I didn't realise intially was with Idratek and Cortex is if you use reed switches for door open / closure then Cortex ignores the first 5 seconds on door clsoure because of false positives on the PIR when a door closes. With this in mind you may want to re-consider PIR positioing for picking up motion after 5 seconds of door closure.


  4. #4
    Moderator Gumby's Avatar
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    May 2004


    Yet more considerations ... if positioned next to a door, if the door is left open will it obscure the view of typical bodies ?

    In my study the MFP is next to the door and I habitually leave the door open, which then sits exactly between me at my desk and the sensor. I have a secondary sensor over the desk to get around this.

    Also, in bedrooms I think you may want some retriggering to maintain occupancy state. Given fewer movements, and possibly less visible body heat due to bed clothes the sensor may need to be favourably located.

    Some of this depends on your door closing habits .. if you habitually close doors then position of PIR is less critical. If you habitually leave doors open then you need to be careful to avoid lights coming on in rooms that you don't intend to enter.

    As for temp position .. I'm sure body height is more perceptually accurate than ceiling and therefore easier to determine a set point. What is going to be a subject for experiment is whether fixed offsets to the set point will be sufficient to get around this. And since the ceiling will mostly over-read I guess I can sneak in a reduction in heating ... "look: the thermostat is set for 21 everywhere .. you need to wear a thicker jumper ..." :-)

  5. #5
    Automated Home Guru jpdw's Avatar
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    Oct 2007


    Quote Originally Posted by jpdw View Post
    Planning for my new kitchen has got me wondering this question ...
    I know this is an old thread, but couldn't resist commenting on this.

    So, 2007, it seems we were planning our new kitchen - I vaguely remember it.
    Early 2008, (vaguely planned) kiddy related news (& x2)... kitchen went on hold, indefinitely (along with a lot of other attributes of not having kids).
    Now, late 2011, I'm looking stuff up as our kitchen is finally underway and actually nearing completion!

    And I'm still figuring out where to put the PTS module! (likely 1 ceiling, 1 lower)

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