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Measuring moisture in residential environment

Discussion in 'Electronic Components' started by Chris Brown, Jul 29, 2007.

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  1. Chris Brown

    Chris Brown Guest

    Hi all,

    A question for those knowledgeable in this area... if I was looking to
    measure humidity in a residential setting, what would be the best type of
    sensor to use? I've done basic reading on the various types, but I'd like
    to hear opinions from folks who really know this topic and what's out there,
    practical application, etc.

    Ideally, this sensor would identify undesirably high humidity conditions in
    a normal household environment, would probably be replaced rather than
    recalibrated once installed, and would be sufficiently accurate to prevent
    any serious likelihood of false positives.

    Cost, size, and reliability are of particular interest.

    Anyone have any thoughts on this topic? I would greatly appreciate any
    input. If this would be better posted in a different newsgroup, please let
    me know.

    Thanks!

    - Chris
     
  2. Looks light the right choice of group to me..

    If improvisation and cheapness are ok, you could try the resistance of
    paper. Crude I know, but workable, as paper is usually slightly acidic and
    should change substantially with humidity. Medium term repeatability will
    be good too, and long term repeatability could be calibrated with a
    portable meter, and adjustment made to a preset pot. One advantage to this
    crude device is that it will respond rapidly to changing humidity, and its
    resistance could range widely enough to make it easy to avoid false alarms.
     
  3. clifto

    clifto Guest

    You could research using human hair as a sensor.
     
  4. Tolstoy

    Tolstoy Guest

    I'm no humidity expert, in fact I'm all wet!
    Here's a sensor you can buy from digikey for about $10:
    http://rocky.digikey.com/WebLib/Humirel/HS1101.pdf
     
  5. Gary Tait

    Gary Tait Guest

    Are you looking for something that "trips" at a high humidity point or
    something linear and trip in electronics?
    I am thinking something like a chemical agent fixed to paper, which is
    optically or electronically read.
     
  6. Chris Brown

    Chris Brown Guest

    I'm thinking of something that would register elevated levels over time, or
    at a given point in time, without the need to trip right away when the
    elevation was encountered. Essentially just monitoring that humidity levels
    stayed within a desired range.

    Thanks,

    - Chris
     
  7. Chris Brown

    Chris Brown Guest

  8. Chris Brown

    Chris Brown Guest

    Thanks for your post Lostgallifreyan.

    I like your idea. For what I have in mind, though, I would eventually want
    to manufacture something in quantity, so though cost is certainly an object,
    it is not the overarching thing. In fact, not needing to visit the device
    to recalibrate it would rate higher on the list of objectives. This sensor
    would be part of a more complex assembly. I'm guessing that the challenge
    is not unique, though I'm not sure if there's a singular clear answer for
    this type of application.
     
  9. Ok. :) Two other ideas came to me... One is those tiny slot counter
    thingers, with an LED and a photodiode. If you can find one with a bright
    visible red LED and nothing but the photodiode on the other side (so it's
    linear, near enough), you could use a piece of cobalt paper in the slot. As
    it changed from blue to pink with increasing humidity, it would pass more
    red light. The reflective types that have both LED and photodiode pointing
    the same way might also work.

    Another thought is to make a few tiny PCB's with an interlacing of two
    tracks, one each side vertically with several fine extensions horizontally
    nearly reaching the opposite vertical. Tin these so they resist oxidising
    in water better than copper will, then try to find (or make) a hygroscopic
    paint that won't corrode the metal when it's damp. If this works, it could
    be by far the cheapest way to make something that will hopefully be good
    enough for production.

    The main thing is how accountable it must be. If anything like insurance or
    other legal considerations matter, you'll need a sensor that has
    characteristics that are firmly established, and for that it will be easier
    to buy one ready made than to try to establish it yourself.
     
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