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From: Steve Turner
Subject: Re: Humidity sensor - peculiar behavior
References: <email@example.com> <3E170A5E.firstname.lastname@example.org> <email@example.com>
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Date: Sun, 05 Jan 2003 01:46:04 GMT
NNTP-Posting-Date: Sun, 05 Jan 2003 01:46:04 GMT
Organization: AT&T Worldnet
>Could it be that the sensor dissipates a little power and heats up?
This occurred to me also. What I'm seeing is exactly the type of
effect that I would expect from sensor self-heating. The sensor
module (with voltage regulator, sensor, and op amp follower) takes a
bit under 4 mA. Even if that was dissipated totally in the sensor,
that would only be 20 mW. I guess I'm not calibrated on these things,
but that doesn't seem like much heating. (?) The datasheet specifies
200 uA typical supply current. At present I can't easily measure
>This would lower the measured humidity. It can be easily checked by
>applying two different voltages to the sensor and see if the drop in
>humidity is more for the case with the higher voltage and hence higher
An interesting idea. I will keep this in mind and will probably try
it if I can't solve the problem otherwise. This would entail
desoldering the sensor from the board, which I'd rather not do if I
can avoid it.
Thanks for the idea.
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