Thanks for the quick reply. I probably should have phrased my question
better: what do salt solutions have to do with the calibration at all? What
do you do, spray a mist of the solution into the area where the sensor is?

I would have thought that calibration would simply involve using a second,
known good humidity sensor, but I certainly have not thought this through
much. Perhaps you are referring to a more basic way of calibrating that
does not require that you already have a humidity measuring instrument?

Thanks,

Sean

At 08:25 AM 4/3/02 -0500, you wrote:
>At 11:51 PM 4/2/02 -0500, you wrote:
>>Hi Spehro,
>>
>>Why do you have to prepare a range of solutions of different salts in
>>order to calibrate a Humidity sensor?!
>
>One or two might do, depending on the accuracy you need (and where you need
>the accuracy to be best). One fellow I know makes these things
>professionally and they have developed an automated system to calibrate the
>sensors at a number of points to give better accuracy. In fact the
>(non)linearity of the Philips parts is fairly predictable so two points
>would not be bad. One could even be okay if you only care close to one
>point (say you are *controlling* humidity at xx%, you only need to know it
>accurately near that point. I thought I'd list the important points and
>associated salts for the convenience of the OP.
>
>Note that the tolerance on sensor sensitivity is +/-12.5% and the tolerance
>on the zero value is +/-15% (of capacitance in both cases). Also there is a
>temperature sensitivity of 0.1%RH/K.
>
>More on the calibration issues in ASTM E 104.
>
>Best regards,
>
>Spehro Pefhany --"it's the network..."            "The Journey is the reward"
>speff@interlog.com             Info for manufacturers: http://www.trexon.com
>Embedded software/hardware/analog  Info for designers:  http://www.speff.com
>9/11 United we Stand
>
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