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Date: Sat, 16 Nov 2002 10:03:01 -0500
From: "Raymond E. Rogers"
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Subject: Re: Temperature Measurement Stability
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John Larkin wrote:
> On Wed, 13 Nov 2002 19:19:44 -0500, "Raymond E. Rogers"
> >I have a manager problem and would like a good Temperature Measurement
> >reference to beat somebody over the head.
> >We need to build an instrument that has .15 degC stability across
> >instruments and over time; this is at a single fixed temperature 37
> >degC. I am trying for the temperature measuring part to be .03 degC
> >(5:1) stable.
> >I am trying to convince somebody that we need to recalibrate annually or
> >biannually; or be convinced different. I would like a reference that
> >has explicit authoritative statements and hopefully data, concerning the
> >long term stability of:
> >Platinum RTD
> >Glass Encapsulated "Super" thermistors
> >Semiconductor temperature sensors, like those used in Dallas
> >Semiconductor units.
> >The last is to be able to make statements about an old instrument that
> >is supposed to be 1 degC stable.
> >I looked up several books, boy are they expensive.
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> several people make thinfilm platinum RTDs, nice small ceramic slabs
> with a 1K platinum film and a glass overcoat. They're just a couple of
> dollars each. Combine that with a few thinfilm resistors in a bridge,
> and it should be pretty stable.
> Two RTDs and two resistors in a bridge would be twice the fun.
I understand the the common ones are only stable to .1-.05 degC for a
year, and the better ones are more expensive. There is also the problem
that I want (perhaps I will not be able to we have physical
implementation problems) to have the system reference attached to a
stage that moves around. The test strips are put on and taken off of a
stage that has to move in and out of the instrument for accesability. I
want this test stage to be nailed to the right temperature. Now the
reaction of the Platinum RTD's to temperature is far less sensitive than
the thermistors. Use of the thermistors would allow less concern for
the intergrity of the various connections leading back to the measuring
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