Temp sensor

[Rudi Machilek]

A 1/8" grounded junction thermocouple has a time constant of about 10-14
seconds.  Time constant (or response time) is defined as the time required
to reach 60% (or so) of an instantaneous temperature change. An exposed
butt-welded thermocouple is about the same, but much more fragile.  Smaller
diameter sheaths (1/32")are more fragile and respond much faster; but fast
is still measured in seconds.  Thermistors offer no advantage (especially in
mechanically stable mounts).

But all is not bleak.  The rate-of-change is still a valid measurement, even
if the temperature measurement is not accurate.

Look at these links from Omega for more info:

http://www.omega.com/temperature/Z/pdf/z051.pdf

http://www.omega.com/temperature/Z/pdf/z054-056.pdf

Thermistors can go to 600+ degrees C without damage.  I like thermocouples
for mechanically and environmentally tough applications.  Mount the
thermocouple in a fitting from Swagelok, Gyrolok, Parker..... to get the
pipe thread mounting.

/Rudi


> The need to live with vibration, oily air environment, and
> the faster the
> response the better, preferably a 1/8 or 1/4 pipe thread mounting
>
>
> > A thermocouple is probably the best choice here then. I've severe
> > industrial controllers sitting around that use them and
> they are fast
> (only
> > the time needed to heat the junction, which can be
> uninsulated if the
> > environment is not too bad). A thermistor is pushing it at 300 dF,
> > technically they are rated that high, but I'm not sure if
> I'd push it too
> > much at that level. What kind of response do you need?
> >
> > At 12:23 PM 4/19/2000 -0400, you wrote:
> > >The tranny temp sensors are the faster reading ones, I've
> heard of so
> far.
> > >I want to read turbo discharge air temp, accurately, and
> 0-18 PSI is just
> > >.x's to do, in a quick car. so needs to go room temp to
> about 300dF in
> less
> > >then 2 secs..
> > >Grumpy

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org