X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f
X-Recipient: geda-user AT delorie DOT com
X-TCPREMOTEIP: 207.224.51.38
X-Authenticated-UID: jpd AT noqsi DOT com
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\))
Subject: Re: [geda-user] [OT] Temperature sensor and control recommendation
From: John Doty <jpd AT noqsi DOT com>
In-Reply-To: <54F9CC6C.7070903@ecosensory.com>
Date: Fri, 6 Mar 2015 10:24:00 -0700
Message-Id: <9488B6EF-F9D8-49FF-8377-23BEF868FC82@noqsi.com>
References: <CAF3uCZ=G0FztqBtpfvssYCz9WrUORX8+J45xmH9+KutaX6c+gw AT mail DOT gmail DOT com>	<201503051621 DOT t25GL09H018380 AT envy DOT delorie DOT com>	<CAF3uCZnSwMfNTVybJ+U89RTOk5=B+5FSSci1tD2nW9Ywo9Armg AT mail DOT gmail DOT com> <CAM2RGhS_=rQL1UyMg8xixfOsrXq=AhZ__S70ijhSi=pLg=ZjQQ AT mail DOT gmail DOT com> <54F9CC6C DOT 7070903 AT ecosensory DOT com>
To: geda-user AT delorie DOT com
X-Mailer: Apple Mail (2.1878.6)
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by delorie.com id t26HO1eG001703
Reply-To: geda-user AT delorie DOT com
Errors-To: nobody AT delorie DOT com
X-Mailing-List: geda-user AT delorie DOT com
X-Unsubscribes-To: listserv AT delorie DOT com
Precedence: bulk


On Mar 6, 2015, at 8:49 AM, John Griessen <john AT ecosensory DOT com> wrote:

> it's difficult and time consuming
> to iterate the design of an analog machine exposed to fluctuating ambient
> outside the oven, and sensor drift as it gets broken in with use over weeks.

Some delta-sigma ADCs have differential inputs for both reference and measurement. This allows you to make a direct ratiometric comparison between a reference resistor and an RTD. Wire them in series, make the voltage across the reference resistor the reference voltage, and the voltage across the RTD the measurement. This reduces the analog accuracy problem to a very small number of components.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com