Proofing my HT oven thermocouple

[Shane Wink]

I recently installed a new open contact thermocouple from Omega for faster readings in my HT oven and have been giving it a thought on how to figure out its accuracy. If I measured the currie point ,1414*F, on the upswing would that be the best way to determine the accuracy of the thermocouple?

I will be sending some coupons to a buddy to check with his hardness tester but in my thinking that is not going to tell me how to figure the difference in real temp and what the PID reads since soak times and methods can affect those numbers.

What do yall think? Is there a low tech way to get accurate temps figured out ?

 

[scott.livesey]

use temperature crayons. they come in 50 degree intervals with 1% accuracy. http://www.mcmaster.com/#temperature-crayons/=pfdyg8 can probably find them elsewhere if you look
the old sailor

 

[Shane Wink]

Thanks Scott. I was not aware of the temp crayons but ordered several this morning.

 

[Shane Wink]

The tempil sticks came in today and so I went right away to get the oven warmed up. I checked it at 450 and 500. both sticks melted within 20* of the target temp however I never got the 1450 to ever melt or mark the steel. I broke pieces of the tempil stick off and tried it but nothing. it would burn but it never would melt.

Any idea on what is wrong? I started at 1400 and worked up to 1600 in 5* steps and never had it melt!

I am using the tempil stick and not the tempil lac. at 13 bucks a stick I am not happy right now. Help

 

[rolynd]

Hi Shane,
When I want to check my TC I usually use a piece of fine silver, either a piece of wire or clipping from a sheet will do. It has to be fine silver - sterling will not do!. Put it in the oven near tip of TC ,raise temp incrementally and watch when it melts. Fine silver has a melting point of 1763,2°F.
If you need something with a lower temp you can use sodium chloride(table salt) It has a melting point of 1474F. Problem with the salt is that it has to be pure as well. any impurities can throw off the Melting temp. Thats why I go for the fine Slver.

 

[scott.livesey]

The tempil sticks came in today and so I went right away to get the oven warmed up. I checked it at 450 and 500. both sticks melted within 20* of the target temp however I never got the 1450 to ever melt or mark the steel. I broke pieces of the tempil stick off and tried it but nothing. it would burn but it never would melt.

Any idea on what is wrong? I started at 1400 and worked up to 1600 in 5* steps and never had it melt!

I am using the tempil stick and not the tempil lac. at 13 bucks a stick I am not happy right now. Help

i would call who you bought them from and get advice or refund. i have not used them at temps above 500F.
scott

 

[Jon Kelly]

Salt melts at 1474 degrees Fahrenheit. (801 c)

 

[KenH]

When you are checking the temperature of oven, you need to have the "check material" (pure silver, NaCl, etc) right next to TC tip. The temperature will vary a fair amount from place to place in the typical oven.

Remember, a typical type K TC when new has an accuracy of 0.75% "Limit of error", and as the TC is heated as hot as we heat them, and the connections corrode a bit, over time expect that 9ºF "Limit of error" at 1200ºF error to increase to at least 12ºF or more. That's why you check the actual temperature of the oven. Note, these numbers all all lower error than those temperature crayons.

Ken H<