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From: John Popelish
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X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: Humidity sensor - peculiar behavior
References: <email@example.com> <3E18E6A4.C30AA912@rica.net>
Date: Sun, 05 Jan 2003 05:32:03 GMT
NNTP-Posting-Date: Sun, 05 Jan 2003 00:32:03 EST
Steve Turner wrote:
> John Popelish wrote:
> >My guess is that the device contains a 5.9kHz internal oscillator and
> >a full bridge driver (probably CMOS) and a capacitance to voltage
> >converter circuit that drives the output but leaks some of the
> >oscillator edge to the output. This would imply that the chip should
> >have a but if bypass capacitor across the supply pins, and a low pass
> >filter between the output and the follower to keep the spikes from
> >causing any nonlinear effects with the opamp input.
> Something odd with the last sentence above: "..should have a but if
> bypass capacitor..." --clarification?
Remove the 'but if'.
I hate it when I get distracted in the middle of a sentence. :(
> Anyway, a bypass capacitor across the supply pins would be very easy
> to add. I'll try that.
> > With a single
> >opamp follower it is very simple to produce up to a 3 pole low pass
> >voltage controlled voltage source (Sallen-Key) filter with a very
> >accurate gain of 1. But just a series resistor and shunt capacitor
> >before the follower may suffice.
> Are you suggesting that the spiking / residual AC signal may be
> responsible for the behavior I'm seeing?
If the spikes are large enough and fast enough, they may be causing
the follower to act a little squirrelly. It isn't a very good
hypothesis, but I have seen some strange effects. The time delay
before the bad effect is hard to tie into anything involving the
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