Lots learned a lot over the past few days, and it really does seem that
thermocouples (especially open-elements) are very very fast.  Type T
thermocouples are apparently the most accurate and available in two classes,
with 0.5 deg-C error versions commonly available.  But thermocouples need a
lot (relatively) of support circuitry, especially since this is in an
automotive application (measuring air temp at a couple points in the intake
tract).  1sec to 2sec works fine, since this is a monitoring application,
and 1% error would be nice, although a bit more would still be acceptable.

Mounting (for the end-user) will be a major factor as well, so any basic
element/component that needs to be PCB-mounted becomes less desirable, as
I'd have to factor in the labor cost to build those to a user-friendly
format ... and that's still be decided upon.

I had missed the graphs with response time in those datasheets (LM35 etc) --
I was looking for electrical parameters.  But checking back now, they're
relatively quite slow.  I found RTD's that are available in better than 1
sec response time using open elements, and they require minimal support
circuitry.  They also come mounted to a stem/flange/etc so end-user install
is ready-to go.  The problem is cost -- so far they're in the $35-$40 price
range each (in 50-100pc quantities).

I always thought that thermistors were not-so-accurate, but I've been
corrected again it seems.  I'm looking at various datasheets now in the 0.5%
to 1% range, and they seem promising.  Very low cost (<$1 ), and I'm working
out a mounting structure to see just how much it would cost if assembled
in-house.  I also found some suppliers of thermistors in flanged probes, so
I have some calls to make this week.

Thanks,
-Neil.



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