Reasonably Accurate Humidity "Gage" for a Reasonable Price? - Page 2
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  1. #14
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    878
    Originally posted by entropyknocks
    I'm fortunate to have a friend two blocks away that has his weather station hooked up to wunderground.com.

    To clarify, I don't mean a 10% difference, 40% vs 44%, I'd be fine with that, I mean a 10 point difference, 40% vs 50%. And worse, I put a new battery in the Extech and now it's a 13 point difference. If the Extech is accurate, then I could be looking at at mid to high 50's RH.
    Humidity is based on temperature. Although the thermistors used in these handhelds can have 10 second response time in still air, it's all lost in the thermal mass of the unit. You must let it normalize for 15-20 minutes.

    I have a Amprobe hygrometer and although the temperature is dead nuts compare to my calibrated Fluke 971, the %RH is off by 10%RH.
    Bill

  2. #15
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,231
    Here is another way to get %RH. Shiney metal bowl with +80^F water. A good liquid thermometer calibrated with crushed ice water(32^F).
    Measure the temperature of the water, while slowly cooling the water with ice until the exterior of the shiney surface fogs. The temperature of the water at the point of foging is the dew point of the air. Remove ice from the water. As the water warms the fog will clear, confirming the dew point. The following web site provides %RH. temperature.http://science.howstuffworks.com/framed.htm?parent=question650.htm&url=http://www.esb.act.gov.au/firebreak/humidity.html

    Cheap meters are much better now than a few years ago. Maybe we should get mental help for this problem. TB

  3. #16
    Join Date
    Feb 2006
    Posts
    168

  4. #17
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,231
    Originally posted by teddy bear
    Here is another way to get %RH. Shiney metal bowl with +80^F water. A good liquid thermometer calibrated with crushed ice water(32^F).
    Measure the temperature of the water, while slowly cooling the water with ice until the exterior of the shiney surface fogs. The temperature of the water at the point of foging is the dew point of the air. Remove ice from the water. As the water warms the fog will clear, confirming the dew point. The following web site provides %RH. temperature.http://science.howstuffworks.com/framed.htm?parent=question650.htm&url=http://www.esb.act.gov.au/firebreak/humidity.html

    Cheap meters are much better now than a few years ago. Maybe we should get mental help for this problem. TB
    Wrong address for %RH.
    http://science.howstuffworks.com/fra.../humidity.html

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