Brian M Kennedy wrote:
>
> Steven Louis Baumbach wrote:
> >
> > If you have a multimeter that will accept thermocouples, you could always
> > use a good thermocouple probe. I just saw a really good one from Omega
> > Engineering for $50. Of course, good multimeter is $200+, but many who
> > work on cars already have them....
>
> Neat idea, tell me more....
>
> * Contact info for Omega Engineering?
Omega is THE name in process control and thermal engineering products.
Find 'em at http://www.omega.com/
> * Others who sell them?
Omega can supply you with a local distributor.
> * Why would the multimeter have to "accept thermocouples"? All thermocouples
> will produce a voltage based on a temperature delta -- and all multimeters
> can measure voltage. Or is it just that the multimeter must be able to
> read fairly small voltages? Or that the multimeter has a temperature
>display?
Thermocouples produce a voltage differential between dissimilar metals.
Any dissimilar metal contact will do this to one extent or another. By
placing T-couple leads into a regular multimeter, you're introducing two
additional dissimilar metal joints. Lead "a" and lead "b" are of two
unique metals, and the contacts in the multimeter are very likely not
those same metal. So you will be getting a voltage from not only the
t-couple itself, but also from where the two leads plug into the
multimeter. Not a very accurate device at that point.
> * I assume this will work best where you are just looking for relative temps
> (like inside of tire vs. outside), but not so well if you want to know the
> actual temp? Or is it the case that the thermocouple probes are calibrated
> in some way to allow you to know the absolute temperature?
Bingo.
> * Are they linear through the important temperature ranges?
Depends on the t-couple. There are numerous types of thermocouples, and
they all have a specific range of temperatures where they are linear.
Choose your t-couple wisely.
> * What temperature ranges do the thermocouple probes allow you to read?
Depends on the unit. They can measure temps as low as liquid helium, and
as high as a blast furnace.
> * What other disadvantages do they have relative to a purpose-built pyrometer?
Flexibility, and the "neat-o" factor. Beyond that, if you don't already
have the right equipment, then just get a regular tire pyrometer. It'll
work great and reliably, for a fraction of the total cost. Get the probe
type pyrometer as the infra-red ones won't tell you what you need to
know. The probe can tell you the temp of the tire itself, the infra-red
can just tell you the temp of the very outer surface, after it's already
started cooling off after your run.
-Josh2
--
Joshua Hadler '74 914 2.0 CSP/Bi - Hooligan Racing #29 - CONIVOR
'87 Quantum Syncro - aka stealth quattro
jhadler@rmi.net
http://rainbow.rmi.net/~jhadler/
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