Please help me understand humidity sensor datasheet

Mar 20, 2007 2 Replies
M

Hi,



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



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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 :)


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C

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.
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H

Buy a sling psychrometer and use that as your standard to calibrate each device.

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