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From: Steve Turner
Subject: Re: Humidity sensor - peculiar behavior
X-Newsreader: Forte Agent 1.92/32.572
Date: Mon, 06 Jan 2003 03:48:49 GMT
NNTP-Posting-Date: Mon, 06 Jan 2003 03:48:49 GMT
Organization: AT&T Worldnet
Many thanks to those who have contributed ideas for solutions to this
I believe I have eliminated the possibility of a faulty sensor. I
have removed the sensor from the circuit board and suspended it naked
in the 75% constant humidity chamber. The reading is spot on with
only negligible drift.
Oddly, though, I cannot reproduce the drift problem by plugging the
end of the sensor cable into same circuit as exists on the printed
circuit board. This configuration also gives a stable reading! The
only difference here is that the circuit is on a solderless breadboard
outside of the chamber instead of on a printed circuit board inside
I was able to recreate the original problem by soldering the sensor
back into the circuit board. Inserting a 100 ohm series resistor
between the sensor output and the op amp input, and a 0.1 uF cap
between this input and ground, may have slowed down the output voltage
decay, but the output still ends up far out of tolerance from where
it's supposed to be.
I'm stumped. I guess I'll power the sensor only when actively taking
Again, thanks to all who replied. I appreciate the help.
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