Omega thermocouples

sdelanty at sonoma.net sdelanty at sonoma.net
Sat Mar 15 05:41:19 GMT 1997


 <snip>  So I called Omega, and tried an open-junction 1/16"
>K-type. It lasted about 10 minutes. I should have known that the
>vibration would break the little weld ball off where the wires meet
>(the actual thermocouple).

Yeah, a naked type K thermocouple is probably a little fragile for the gas
velocities inside a header pipe. They also don't like atmospheres that
alternate between oxidizing and reducing.(lean/rich) Even small amounts of
sulpher are very bad for them too.
The one good thing about naked K's is that when the ball breaks off You can
take Your oxy/acet torch and melt the two wires back together and it's good
as new.
They can be good for temps over 2300F if other conditions don't kill them.

>	Then I tried a 1/16" enclosed end, 321 stainless. This responds a
>little slower, but will last for about 3 months or so (not so good at
>$31 each). The end just burns right off, especially when doing lots of
>full-boost blasts at 1600 F temperature.
>321 is not supposed to do this. Omega thinks it's a combination
>of corrosive gas, extreme temperature, and vibration.

1600F is very ragged edge for 321 SS. 
321 has a small percentage of Titanium in it and is very corrosion resistant.
It has a maximum service temp of 1550F continuous, 1650F intermittant.

I work at a place that makes ceramic tile, and we use lots of type K
thermocouples.
Our stainless encased k-types are usually made of 310 Stainless.
310 has v. good corrosion resistance (although not quite as good as 321) and
has max service temp of 1900 continuous and 2050 intermittant.
Our 310 K-types regularly see 1750F, although not in as nasty of a storm as
exists in a header pipe...

Other noteworthy probe materials may include:
309 stainless. similar to 310 but only good for 1850F cont, 1950F int. Still
better than 321.

446 stainless. This material has excellent corrosion properties, especially in 
sulfer-rich atmospheres. It is also good for 1950F continuous and 2050F int.
This may be the ideal material if You can find a probe made from it.
I've never seen one, but I've never looked....

Ceramics. we use type K in a special ceramic tube in the fire boxes of our
tunnel kiln. The tube temperature ratings far exceed the 2300F capability of
a K-type probe
Ours have seen almost 3 years of service, and live at 2080F several days a
week and
1750F the other days. They take sunday off. The material is very tough and
hard to break and is extremely resistant to thermal shock. The ones we use
are about 5/8" in diameter and 14" long but I know smaller ones are available.
They may be too slow to respond for EGT work, I dunno.


>p.s. I usually saw about 1050 F at idle (retards to 1 BTDC for lower
>idle emissions). About 1250 F at part throttle cruise, and up to 1600
>=46 at 15 psi boost. It's interesting to observe the effect of changing
>the AF meter flap tension on exhaust temps...

Wow. 1050 at idle seems like a lot.

 Steve Delanty (sdelanty at sonoma.net)




More information about the Diy_efi mailing list