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Message-ID: <54FA053F.3010102@ecosensory.com>
Date: Fri, 06 Mar 2015 13:51:27 -0600
From: John Griessen <john AT ecosensory DOT com>
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To: geda-user AT delorie DOT com
Subject: Re: [geda-user] [OT] Temperature sensor and control recommendation
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Reply-To: geda-user AT delorie DOT com

On 03/06/2015 11:24 AM, John Doty wrote:
> 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.

That sounds great!

If you also used high purity wire able to take the heat, and kept
the ref R close to the RTD on a conductive block right in the oven, there would be no thermocouple effects to speak of.
You would still want the amplifier/ADC to be out of the breeze and as close to same temperature as
its enclosure surroundings as is practical.  Maybe put it on a large copper pour ground plane and
solder a brass box over that...or run a little fan inside the circuit enclosure... anything to stop temp gradients
on the chip as ambient fluctuates.