Kiln temperature testing

[Stromberg Knives]

Hello!

I've been trying to find out how precise the temperature is in my Paragon KM24T. So I conducted a little experiment and thought I'd share the results.

For the experiment I bought an Omega XC-14-K-12 thermocouple. It's rated to 1090 degC and is said to meet or exceed SLE and EN 60584-2 Tolerance class 1 (plus/minus 1,5 degC at 1000 degC).

I let the oven stabilise for a while at every temperature before moving on.

These are my results.

The results seem rather consistent, about 1,0% deviation a lower temperatures, which goes up to about 2,4% at the higher end. From the results I believe the Omega TC is closer to the actual temperature since I've always have had to heat treat on higher temperatures than what the HT recipes recommend.

So... now I have two sets of relative measurements, but I can't be truly sure which is closest to the actual temperature, haha.

As a side note, I believe I have the stainless-steel sheathed-style PY54 K-type thermocouple in my Paragon. I don't know its tolerances though, and it's been used for some years now.

Is it recommended to replace the kiln TC after x hours of use, just as a precaution?

 

[Stacy E. Apelt - Bladesmith]

Yes, they degrade with use. If you use the oven regularly, replace it yearly.

 

[Natlek]

Is it recommended to replace the kiln TC after x hours of use, just as a precaution?

https://www.asminternational.org/do...p048.pdf/236107c7-ec38-40e6-8ecc-51a23dfefaa4
https://www.industrialheating.com/articles/95530-how-long-should-my-thermocouple-last

The operating life of a thermocouple depends on its operating temperature, time at operating temperature, ambient temperature, cyclic range (high to low temperature variation) and, most often overlooked in heat-treating applications, the influence of contaminants either on an exposed thermocouple or on the protection tube itself. Many thermocouples are replaced on a periodic basis, typically every six to nine months depending on the severity of the end-use application.

 

[JTknives]

What did you have the omega TC connect to? I have 5 of those special omega TCs with their fancy sheath. And so I put 2 in through the same hole in the oven and connected one to each controller and there was a 25° difference between the 2. So case in point, DONT believe anything your controller tells you. This is especially true if your using an inexpensive pid controller. 25° can make or break a good heat treat.

 

[Ken H>]

JT, your results suggests those "high dollar" TC are not any better (or worse) than the el cheapo TC purchased. Interesting.

 

[Robert Erickson]

About a year ago I got a second thermocouple to test my kiln as a way to trouble shoot heat treating W2. I found that my Evenheat thermocouple readout was 60 degrees off.
The way I sorted out which thermocouple was reading closer to actual was by doing a bunch of coupons and found that the ones that produced the highest AQ RC were correlated to the second thermocouple I installed.

 

[JTknives]

I had always been getting the TC from auberns but i have burned through 3 of them this year. I stepped up to the Omega TC with their magic sheath and i'm more then happy with them. but thy read about 20-25 deg cooler than the cheap auberns TCs.

This is one reason i bought a dry block TC calibrator. I could care less what thy read as long as all my ovens read the same. Right now i have 4 ovens that all need to be consistent to each other. The dry block is handy as it heats up its chamber and you put the TC in and check the dry block display and compare it to the controller display. If it's different you adjust the offset in the controller.