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Please help me understand humidity sensor datasheet

Discussion in 'Electronic Basics' started by My name is Bob, Mar 20, 2007.

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  1. Hi,

    I want to make a humidity sensor with the Humirel HS1101LF:

    http://www.humirel.com/product/fichier/HS1100LF&HS1101LF-HPC052C.pdf

    This sensor is a capacitor whose capacitance changes with RH. I built the
    circuit on the datasheet which turns the capacitance into a frequency and I
    am measuring this with a microcontroller.

    The datasheet says the sensor has a nominal capacitance @ 55% RH of
    177-183pF, a variation of 6 pF. If the sensitivity is 0.31pF/%RH, does
    this mean it comes out of the factory with an initial accuracy of +/-10%?

    Does anyone know how to get 2 or even 5% accuracy for about US$20 (in small
    quantities)?

    Thanks XXXOOO :)
     
  2. carneyke

    carneyke Guest

    Even the best companies out there have problems getting accuracies of
    +/- 2 % RH in the low cost environment. Meaning if the actual
    environment is 50 % RH , the measurement could be 48 % RH to 52 % RH.
    Some fall apart below 20 % RH and above 80 % RH with specifications
    ranging from 3 % RH to 10 % RH. One of the most accurate methods
    (expensive) is a chilled mirror and that usually has a specification
    of +/- .5 % RH. Some use wet / dry bulb techniques.
     
  3. Buy a sling psychrometer and use that as your standard to calibrate each
    device.
     
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