[Greenbuilding] Calibrating Hygrometers

[Bruno M.]

It is relatively easy and doable in an household situation,
without real costs nor special knowledge or tools, not
even renting or lending a calibrated precision hygrometer to compare.

This is a description of the first step
to calibrate @ 75% RH
http://exoticpets.about.com/od/herpresources/ss/hygrometer.htm

with using other salts you can DIY pretty easy & still accurate for the 
whole range from 6% to 99% RH:

SALT BATH PUBLISHED          RH AT 25 ° C
LITHIUM BROMIDE                6.37%
LITHIUM CHLORIDE               11.30%
POTASSIUM ACETATE             22.51%
MAGNESIUM CHLORIDE       32.80%
POTASSIUM CARBONATE      43.16%
MAGNESIUM NITRATE          52.89%
SODIUM BROMIDE                57.57%
POTASSIUM IODIDE               68.86%
SODIUM CHLORIDE               75.30%
POTASSIUM CHLORIDE          84.34%
POTASSIUM SULFATE            97.30%

You find more about how those salts are used in this publication:
http://nkhome.com/pdfs/calkit_web08.pdf


Don't forget that temperature is also a factor that influences 
measurement of humidity,
as is non-linearity of your device:
read about it in this article about the trouble to get a correct reading 
with industrial electronic hygrometers,
from the specialists themselves, Viasala:
http://www.veriteq.com/humidity/index.htm

Hope this leads you to calibrating your own devices.

Grts
Bruno M.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Op 10-11-2012 18:13, Benjamin Pratt schreef:
> I happen to have 4 different cheap electronic hygrometers. When placed
> next to each other, each one gives a different reading, with a
> variation of about 10%.  It would be nice to know which brand is the
> most accurate.
>
> -ben
>
> ======================================