How long does your thermocouple last?

East Branch Knives

East Branch Knives

Joined
Feb 5, 2014
Messages
169
I've gone through two thermocouples in as many years, both with relatively infrequent use. I use the K-type high temp TC for kiln from Auberins, plus the ceramic sheath. Both of mine eventually got fried and would simply register "Hi" rather than the temp.

Just wondering if they're supposed to last a little longer and if there's something I'm doing wrong.

Thanks!

Mike
 
I can't answer your question as I'm new to temp control and I just got my thermocouple, but I can tell you that Omega's customer service was exceptional in my purchase experience and their tech support was great during purchase advise. Give them a try,
 
I've had the same TC and sheath your using for about 18 months with no problems. I only use my forge for heat treating, so it's not used very often and I don't get it much above 1600-1700 degrees. I'm also curious if others are having a short life spans with this set up.
 
I've heard that anything burning in the oven is bad for elements and tc's, such as the stuff people use to "consume excess oxygen."
The only TC I've had go out was because the element got loose and shorted it out.
 
What temps are you working with using the K thermocouple? Check and see what operating range they say this one is good for. If you exceed the recommended range by over a 150 degrees, consistently, it will shorten their life.
 
Fred.Rowe said:
What temps are you working with using the K thermocouple? Check and see what operating range they say this one is good for. If you exceed the recommended range by over a 150 degrees, consistently, it will shorten their life.
Click to expand...

I usually run my forge at 1800 - 2000 F. The TC is supposedly designed for "operating continuously at 2300 °F." I don't think I've ever hit 2300; I usually turn the burner way down when I hit 2000 and crank it back up when it cools to 1700 or 1800. I do my heat treating in an oven (with a built in TC) so I just use the forge & TC for forging.
 
hsc3_90293 said:
I can't answer your question as I'm new to temp control and I just got my thermocouple, but I can tell you that Omega's customer service was exceptional in my purchase experience and their tech support was great during purchase advise. Give them a try,
Click to expand...

That's good to know, I'd never heard of Omega before. I'll have to check them out.

Thanks for the tip!
 
hello, can you chk. to see if the thermocouple is in the proper position in the flame? should be the last 1/4" or so. sometimes that causes a problem like you describe.
 
I do business with Omega as well. Excellent service, custom sizes on TC. Huge catalog, anything electrical.

Keeping it out of the flame trajectory is a must. I use no sheath just the standard unit with only the last 1/4 inch inside the forge.

Fred
 
place them in a well , is it probe shielded wire or wire? I may be able to offer some help. I am an instrumentation technologist and i used to deal with TC's and rtd's on a daily basis back in my zinc mine concentrator days in our drying kilns.
 
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As GG was saying, in a forge atmosphere, the TC needs to be protected from the flames. They will burn out pretty fast if exposed to the open chamber environment. Under no circumstance should they be directly in the flame path from the burner. A ceramic TC sheath ( Omega sells them as does eBay) is required to hold the TC. Get one that is long enough to place the end in at top center chamber. This will give a fair reading of the chamber temp as well as provide a long TC life.
 
I have this same TC but used in my HT oven, (not forge), and its been treating me great for about 5 or 6 months now. I would more than likely agree that it has to be the direct flame causing them to burn out quick..
 
GasMan1 said:
hello, can you chk. to see if the thermocouple is in the proper position in the flame? should be the last 1/4" or so. sometimes that causes a problem like you describe.
Click to expand...

I keep the TC out of the flame, off to the side. My forge is basically a propane tank on its side with openings in the front and back. The TC is stuck in through the back and runs the length of the forge up to about where the flame hits the floor, but about 2-3 inches off to the side.
 
grumpy_grinder said:
place them in a well , is it probe shielded wire or wire? I may be able to offer some help. I am an instrumentation technologist and i used to deal with TC's and rtd's on a daily basis back in my zinc mine concentrator days in our drying kilns.
Click to expand...

I use this one: http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=39

I also use the ceramic sheath to protect it, as recommended on that web page for use in "fuel heated kilns."

Apparently this TC is the one that comes installed in most kiln/heat treat ovens (including mine, but that one's still working great).
 
Stacy E. Apelt - Bladesmith said:
As GG was saying, in a forge atmosphere, the TC needs to be protected from the flames. They will burn out pretty fast if exposed to the open chamber environment. Under no circumstance should they be directly in the flame path from the burner. A ceramic TC sheath ( Omega sells them as does eBay) is required to hold the TC. Get one that is long enough to place the end in at top center chamber. This will give a fair reading of the chamber temp as well as provide a long TC life.
Click to expand...

Stacy, thanks very much for the advice. I'd like to get my next TC from Omega, but there's a pretty dizzying array available on their site. Any tips on which one(s) to look at? I know it needs to be "K type," but that's about all I know.
 
TC specs are:
Type K
8 gauge
12-14" leads with ceramic spacers
Type K TC block
Type K TC wire to connect to the PID or readout ( Everything from TC tip to PID connection is polarized and type K. It all must be the properly wired with type K wires to get accurate readings)
Type K plug and socket for connecting to the PID/readout (this allows the forge TC to be unplugged and the PID to be plugged into other TC's or devices to read the temp on temper ovens, checking the quench oil temp, etc.)
3/4" ceramic sheath tube ( keeps TC out of corrosive gasses) Get the 12" tube.


The Auber Instruments unit you linked to is exactly what you want. It has the TC, TC block, and TC wire already matched.:
http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=40

This is the Auberins TC sheath:
http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=40

This is the Auberins TC connectors:
http://www.auberins.com/index.php?main_page=product_info&cPath=7_43&products_id=427

This is the Auberins PID that works quite well for a forge readout and can easily convert your forge to PID control by adding a few parts:
http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=106

Total cost about $100. You might save a few bucks on eBay, but why not get properly tested and matched parts of known quality from a major supplier for almost the same price. You also get great tech support and info from Auber or Omega that you won't get from the Chinese folks on eBay.

Omega has all the above, too. You will have to research each part number individually, so I would suggest going with Auberins. If you want Omega parts, I suggest calling Omega and telling them what your parameters are and letting them give you all the part numbers. It may also be a bit higher price from Omega.



To make the forge run on PID control, add an SSR with heat sink and a solenoid valve made for the propane. In the stickys are the plans for my two-stage PID control that will run the forge at an exact temp plus or minus a few degrees. It works on either venturi or blown burners ( blown is best, though). Make sure you purchase a solenoid valve that is made for propane. It will say something like "propane, natural gas, fuel gas". Just the word "gas" or "air/gas" is not sufficient, as that refers to non-fuel/non-flammable gasses. Conversion to PID control can be done anytime, as it does not change anything in the forge or TC setup. It costs about $100-150 to do if you shop around a bit, and makes your forge three times better, IMHO.
 
Stacy, thanks very much for that info, it's exactly what I needed. And you read my mind-- My next project is going to be hooking up the forge to a PID control.
 
Ok, I just got all the above recommended parts from Auber. What power source should I use for the controller?
Also, the ceramic sheath for the kiln thermocouple is 3/4" in diameter. Should I drill a 3/4" hole in my vertical forge? I was thinking I could plug the hole with a ceramic kiln plug when I didn't have the thermocouple in the forge.
Thanks for any help you can give.
 
sometimes i feel people are using controlers that don't quite understand how to set them up. Maybe it's just me and all this technology and new age stuff the controllers are much more simple. But heat control is a fairly tricky process. Especially Depending which elements are in the final and primary control loop. What is everyone using for components in their process' as I'm curious! To me setting the proportional , integral and derivative for a simple electric kiln with a contactor would be tough. I could see if it was a fuel/air fired kiln maybe with a actuated valve as a final element of control. Am i over complicating this? You can get spring fed TC if this is of interest to you. We had to use one in our coke ovens at the smelter because they where always burning (regular TC's) in my mind shouldn't a simple thermostat suffice or thermal transducer? just keep an eye on it and manually heat treat?
 
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