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
-----Original Message-----
From: owner-land-speed@autox.team.net
[mailto:owner-land-speed@autox.team.net]On Behalf Of John Goodman
Sent: Wednesday, May 07, 2003 7:12 AM
To: land-speed@autox.team.net
Subject: RE: Quick Data Connectors
Russel, what is your take on the accuracy of
commercially available tire pyrometers? Are these
devises reliable and to what degree of error?
John Goodman
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/land-speed
/// what is needed. It isn't that difficult, folks.
|