Date: Sun, 17 Nov 2002 10:09:07 -0500
From: "Raymond E. Rogers"
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Subject: Re: Temperature Measurement Stability - +/-3.5 microdegrees
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Jim Thompson wrote:
> On Sun, 17 Nov 2002 03:40:28 GMT,
> "Walter Driedger" ,
> In Newsgroup: sci.electronics.design,
> Article: ,
> Entitled: "Re: Temperature Measurement Stability - +/-3.5
> Wrote the following:
> |37 C is an average, typical human body temperature. Firstly it is an
> |average; actual temperatures may vary. Secondly it is typical. Daytime,
> |nightime, time of the month, oral, rectal, arm pit; change is the only
> |constant. Finally, it is the human average. As such it does not apply to
> |dogs, gerbils, parakeets or iguanas.
> |It is not some universal constant like the speed of light or even the triple
> |point of water. The is no more point in measuring human body temperature to
> |an accuracy greater than .1 degree than there is in declaring the
> |temperature of the weather in a given city, at a given time to be 37.01. It
> |varies more than 2 degrees from one side of the street to the other.
> I think what the OP *really* needs is stability/repeatability; *not*
> absolute accuracy.
The problem really goes beyond this. In order to be credible the
measurements must be guaranteed from time to time on a given machine and
from machine to machine, and also comparable to other laboratory
methods. This must continue to be true in the face of usage and design
changes. This leads me to accuracy; NIST (NBS) tractability. This will
be a commercial instrument that should be able to be relied on. My
"overdesign" is driven by the fact that the electronics/thermal should
not be a limiting factor in the measurement. The purity of the
chemicals and stability of the testing surfaces (in the face of
different production runs) should be the limiting factor. At this stage
of our technology I think it would be unconscionable to have the control
and instrumentation be unreliable; the weak point.
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