From: Steve Turner
Subject: Re: Humidity sensor - peculiar behavior
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Date: Sun, 05 Jan 2003 01:37:01 GMT
NNTP-Posting-Date: Sun, 05 Jan 2003 01:37:01 GMT
Organization: AT&T Worldnet
Spehro Pefhany wrote:
>P.S. I see you've eliminated the possibility of oscillation of the
>follower in your original post, but what about the sensor output?
I've looked at both the sensor output and the follower output with a
scope. The sensor output shows some noise, perhaps 10 mV p/p, plus
very sharp spikes of about 400 mV p/p at about 5.9 KHz. The follower
output shows a 5.9 KHz fundamental signal as well, attenuated (maybe
50 mV p/p), full of harmonics with a decaying envelope. I don't know
if any of this is relevant to anything. It is definitely not square
wave and looks nothing like oscillating op amps that I've seen in the
>If you have a BFC at the follower input that is not isolated from the
>sensor buffer by a fairly large series resistor (like maybe 10K),
>effects like this are not impossible.
>Do NOT load the sensor output directly with a capacitor.
Understood. There are no intentional (except parasitic) in the
circuit. I learned my lesson about driving capacitors with op amp
followers the hard way, some time ago. :/
Thanks for the feedback.
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