Russel, thank you very much for the pyro
information.It is a big help.
John
--- Russel Mack <rtmack@concentric.net> wrote:
> John:
> If you are talking about the infrared radiometers
> (non-contact; Raytek seems
> the most popular brand among the car people)--
> then-- when used on tires or
> asphalt-- the accuracy potential is VERY GOOD.
> Typically, plus or minus 2%,
> if you have the emissivity setting over 0.90 (tires
> probably have an
> emissivity very near 1.00)
>
> The contact-type pyrometers (thermocouple-based)
> always have a significant
> bias error (toward ambient temperature) when used in
> these
> surface-temperature applications. That's because
> the sensor is a good heat
> conductor, and it actually changes the temperature
> of that small part of the
> surface. (TCs and their ilk are best in "immersion"
> applications.)
>
> I'd like to point-out that Hot Rod mag has recently
> carried an ad (or was it
> an editorial?) showing how much header coatings
> reduce the temp of the
> outside surface of the headers; the advertisers were
> proving their point
> using an infrared radiometer (of the same type that
> we use on tires). Well,
> one could easily see that the EMISSITIVY had been
> greatly reduced on the
> headers (i.e.-- they had become more "mirror-like").
> Infrared radiometers
> are notoriously inaccurate on such surfaces-- they
> will typically read very
> LOW. So the customer gets suckered again!
> (Actually, I think some of the header coatings
> probably help a lot-- but
> this was no way to prove it.)
> Russ, #1226B
>
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