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Re: 3610 is Junk

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  • davidefabbri2000
    ... I found that the thermo/igro sensor of my ws2300, I bought last month ( here an inner view:
    Message 1 of 4 , Sep 29, 2006
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      --- In Lacrosse_weather_stations@yahoogroups.com, "bdebreil"
      <bdebreil@...> wrote:
      >
      > This sounds like a reply to my own post :)
      >
      > As far as accuracy and speed of response for the humidity probes, I
      > toured Google for more hints. I read a lot of stuff, but I am still
      > not sure what kind of an hygrometer is mine. In most likelihood, it
      > uses a polymer which properties undergo changes as the rate of
      > humidity grows. Whether it is a matter of length (as in an hair
      > hygrometer) or one of other physical properties such as resistance or

      I found that the thermo/igro sensor of my ws2300, I bought last month
      ( here an inner view:
      http://tech.ph.groups.yahoo.com/group/Lacrosse_weather_stations/photos/view/a199?b=2
      ),
      is one of these SHT1x SH7Tx manufactured by Sensirion, datasheet and
      application notes available here ( the sensor is available at
      farnell.com ):
      http://sensirion.com/en/02_sensors/0...ty_sensors.htm

      The temperature sensore is a 'bandgap' type, the humidity sensor is a
      'capacitive polymer' type, the sensor integrate a 14-12 bit a/d.

      humidity sensor accuracy: 3% o 1,8% ( in the 20-90% range )
      temperature sensor accuracy: 0.5%-1% circa ( in the range of interest )


      > I have also seen a lot of things about calibrating hygrometers, "which
      > can be done by anyone". To do so, you need no more than a tight
      > container (such as a pressure cooker or any other cookware that has a
      > tightly fit lid, better if it is a glass lid). Inside, you put sodium
      > chloride (common salt), say, roughly a glassfull of it, and you water
      > the salt with a small amount of water, a tablespoonfull for instance,
      > and then stir a bit. Next you put something as a bowl or anything else
      > that will allow you to set the hygrometer or probe a few inches above
      > the wet salt. When this is done, you put the lid on and tighten it,
      > and leave it all in, say, a basement (a place where the temperature is
      > relatively constant). The reading will be done "after at least 6
      > hours, preferably after 12 hours", so it is being said. Reading must
      > be 75% HR +- 3%. If it reads less than 72 or more than 78, you must
      > recalibrate the instrument if this is possible, or else you note down
      > the gap in a log book so as to take it into account for correcting
      > readings. In order to calibrate an instrument, you need at least two
      > points, and more if this is possible. Your second point may be the
      > vapour saturated environment (100% HR, obtained in putting pure water
      > in your pressure cooker or whatever tight container, or in wrapping
      > the instrument into a wet cloth). Better yet, you can let your probe
      > in the tightfit container with salts other than sodium chloride, such
      > as Magnesium Chloride in its crystallised form (6 H20), a glassfull of
      > it mixed with one tablespoon of water, which should give your
      > hygrometer a reading of 33% HR, or Potassium Carbonate crystallised
      > with 1.5 H20, wetted in the same manner, which should give 43% HR.

      I found the following table ( Kestrel's kit for calibrating hygrometers )

      SALT BATH PUBLISHED RH AT 25 ° C
      LITHIUM BROMIDE 6.37%
      LITHIUM CHLORIDE 11.30%
      POTASSIUM ACETATE 22.51%
      MAGNESIUM CHLORIDE 32.80%
      POTASSIUM CARBONATE 43.16%
      MAGNESIUM NITRATE 52.89%
      SODIUM BROMIDE 57.57%
      POTASSIUM IODIDE 68.86%
      SODIUM CHLORIDE 75.30%
      POTASSIUM CHLORIDE 84.34%
      POTASSIUM SULFATE 97.30%
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