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Sensirion Humidity Sensor Question — Parallax Forums

Sensirion Humidity Sensor Question

Sal AmmoniacSal Ammoniac Posts: 213
edited 2010-02-18 20:04 in Accessories
I've added a Sensirion humidity sensor to my weather station and frequently see humidity readings over 100% in the early mornings. It often goes as high as 106%.

When this occurs do I need to turn on the sensor's built-in heater until the humidity reading drops below 100%? Does a reading >100% indicate condensation on the sensor that can affect future readings?

Comments

  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2010-02-17 22:07
    ·I would thing There is problem because real early in the morning that why you see due all over the place and that when you have over 100% humidity
    It would not hurt to turn on the heater for a short time· but even then it may still read over 100 % when the sensor cool back down


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  • Tracy AllenTracy Allen Posts: 6,658
    edited 2010-02-18 04:16
    Hi Sal Ammoniac,

    The accuracy of the sensor falls off at high humidity, +/-5% at 100% for the SHT11 according to the attached graph from the Sensirion documentation.
    attachment.php?attachmentid=67881

    Are you using the recommended linearity and temperature compensation formulas?

    I don't think the internal heater is going to help. It may have something to do with how the sensor is situated. The best location is inside a weather shelter or radiation shield or in the shelter of a tree, where it is shielded from radiation from the cold sky or from the ground.

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  • WBA ConsultingWBA Consulting Posts: 2,933
    edited 2010-02-18 05:41
    I'll second what Tracy posted and add one question:

    1) Is your code optimized for teh voltage you are supplying the sensor?

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    Andrew Williams
    WBA Consulting
    WBA-TH1M Sensirion SHT11 Module
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  • Sal AmmoniacSal Ammoniac Posts: 213
    edited 2010-02-18 20:04
    Tracy:

    Yes, I am using the recommended linearity and temperature compensation formulas from the datasheet. I have the Sensirion sensor mounted in a small plastic box about 2" x 1" x 1". I've drilled a grid of 1/8" holes in the metal cover of the box to admit ambient air. The box containing the sensor is mounted with the holes facing down in a standard cotton region wooden instrument shelter.

    Andrew:

    Yes, I am using 3.5v coefficients from the datasheet (I'm running the sensor at 3.3v and the 3.5v coefficients are the closest to that value).
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