limit the range of PIR sensor

Discussion in 'General Electronics Chat' started by bug13, Nov 29, 2015.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi guys

    Is there a way to limit the range of a PIR sensor to about 2 meters? Thanks.
     
  2. ISB123

    Well-Known Member

    May 21, 2014
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    Maybe there is a trim pot some where?
     
  3. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Don't think there is one on my one
     
  4. ISB123

    Well-Known Member

    May 21, 2014
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    Then you are going to have to cover the lens with some sort of semi transparent material.
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
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    This does not compute-

    PIR sensor work by detecting the IR radiation (light) from hot objects.
    you cannot "adjust" the range of your vision, can you? Either you see nothing, or all the way to the horizon.
    All you can do is block the radiation from reaching the sensor, There is no logical way to adjust the distance of sensing besides adjusting the geometry of the sensing angle of view.
     
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  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Most pir sensors use op amps to boost the signal level, if you can look inside it and post pictures, maybe get better answers,

    Or mask the sensor at the sides
     
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  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The PIR sensors normally have parabolic mirrors or Fresnel lenses that have essentially an infinite focus (which turns out to be about 30 - 50 feet.). You will need to either get a PIR with different focal length or experiment with the threshold level of the amplifier within the unit. Note that they usually have some type of sample-and-hold amp or other filter as well to prolong the response. No need to fool with those, just don't get distracted by them when you look for the threshold voltage divider.

    Also, there are often multiple little semsors with multiple mirrors on a wide-angle sensor. They are usually wired so activation of one trips the overall sensor. Also, those multiple semsors could be wired as difference amps so temp change doesn't cause a signal.

    What is your end goal? Really range or threshold?
     
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  8. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi sorry for the late reply,

    Here are what I tried:
    cover the PIR sensor with transparent plastic with different color (green ,red, yellow, orange, white), it can reduce the range of my PIR sensor, but also make it very un-reliable.
    I have also tried cover the sensor with combination of different color, and/or multiple layers, same result.
    I have also masked the sensor at the side, it make the sensing area narrower, but not reducing range.

    At the end, I found a sensor with the shorter range I need, it should do what I want but I have not received the sensor and tested yet.

    I am convinced that the range has something to do with the focal length of the len as GopherT suggested.

    Thank you all for all your inputs.
     
  9. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    My end goal is to find a PIR sensor with a range of about 2 meters.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Last edited: Dec 5, 2015
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  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    PIR 'lenses' in my experience don't have a focal length: they are simply window facets angled to direct radiation from various angles on to the sensor. But then, my PIR experience is somewhat limited :).
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It depends on whether the type you have uses lenses or mirrors. Some have parabolic mirrors to set the focal length, some use the plastic to make a lens of a given focal length (or "infinite" focal length).
     
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  13. Sensacell

    Well-Known Member

    Jun 19, 2012
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    The lenses are key- try removing the lens and see what happens- no workie any more.

    The lens acts to create alternating 'beams' of sensitivity, such that objects moving in front pass through these regions creating an AC output that gets detected and counted by the discriminator. The PIR sensor has terrible baseline drift, the lens effectively moves the signal up from DC so it can be processed as an AC signal. The range is influenced by the shape of these 'beams', too narrow and they cannot detect close objects, too wide and far objects are not detected.
     
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  14. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    The Panasonic one is the exactly the same one I am getting, but the data sheet says depending on the temperature different between the object and environment, it may seen object beyond 2m.

    Hopefully it not too much beyond 2m, anyway, its on it's way, I should get it today or tomorrow...

    Thanks again.
     
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