Pyrometer questions?

There's some stuff in the archives about this. I don't have the address.

Bob Wassam

 

whats a pyrometer ????????

 

I mounted a pyrometer in my carb 308 (it measures exhaust temps at the cylinder head) - good for tuning purposes. works great!! i used the existing header probe nipples that are on my euro 308
john

 

Scott -- I think you answered your own question in that the downside to a non-contact pyrometer is that either the device or the operator has to "know" the emissivity of the thing being measured (so if you buy a "non-adjustable" one you get some sort of internal default value for emissivity). If you really needed decent accuracy out a non-contact version, I think you'd have to use a contact-type version on the same sample of interest so that you could learn/calibrate the (adjustable) non-contact one (and then assume that when measuring similar samples with the non-contact pyrometer that the emissivity is the same) -- JMO.

 

No

 

For tire temperature measurements, emissivity corrections are not real important. This is because you are interrested in the relative temperatures across the tire width and camparing temperatures from tire to tire. Since all the target temperatures are the same material and surface finish, error due to emissivity will be negligible. For tire rubber, an emissivity of 0.9 is about right though.

Emissivity can have a significant effect on some surfaces, especially highly polished ones which have very very low emissivity values. Polished aluminum has an emissivity of about 0.04. In this case, the instrument will measure a lower temperature than actual. In fact, only a true black body will achieve an emissivity maximum of 1.0.

At work we use Flir infrared cameras to image PC boards for hot spots and trouble shooting purposes during development testing. These cameras, about 60k each, are military grade and you can see area gradients to a fraction of a degree. Even in this kind of work, absolute errors of 1-3 degrees are seldom important. We almost always assume an emissivity of 0.9, which works well for all components except metal ones. If the surface is very shinny, what one really sees is a reflection of the surrounding ambient.

My recommendation is to set emissivity to 0.9 for tire work and painted surfaces and use the measurements directly. By the way, the color of paint has almost no bearing on the measurement. This is because color is in the visible spectrum and the bulk of heat transfer occurs in the infrared region which the human eye cannot see.

 

Exactly. The goal in tire temp measurement is to do them as fast as possible before the temps equalise, which is why I like an IR non-contact gun for this application. With a probe you have to wait a lot longer for the temp to reach true value, and all the while all your other temps are averaging themselves out. Ideally you have twelve guys with 12 IR guns hanging over the pit wall measuring inside, center and outside temps on each tire as you exit the last corner. Settle for you to measure and your pit bunny to write em down. (Rem when girlfriends did timing and scoring? A reason to hate transponders if you ask me) Fancy pyrometers will record the temps but that's for sissies

But it's a good point that for almost any app it's relative temps that matter so a small absolute error from emissivity is not really important.

 

Search longacre tire pyrometer