Herbert Graf wrote:

> I bought a household digital . . . the humidity sensor
> it uses seems to be a resistive sensor. I looked up this type of sensor and it
> mentions that you can't
> just drive it with DC, it will "polarize" the sensor, why this is bad I
> don't konw (perhaps for electrolysis reasons?).

Your guess is right. Years ago I worked on a greenhous control project. It is
amazing how fast a copper from a PC board will move across a open resistive
humidity sensor with DC component applied to sense it.  The same is true for
Wet / Dry  thermistors. Great care needs to taken to assure that the leads on
the
wet thermistor are not in contact with the wet wick. The capacitive sensors used
in
home humitifiers work very well and are inexpensive Capacitive sensors are
reliable but not paricularly accurate (3-5% error)  I haven't looked recently
where they can be purchased.

Walter Banks

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu