Please help me understand humidity sensor datasheet

[My name is Bob]

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

 

[carneyke]

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

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.

 

[Homer J Simpson]

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

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