k thermocouple for hi temp salts

hardheart

hardheart

Joined
Sep 19, 2001
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what thermocouples are appropriate for use in salts. I bought 2 PID controllers, only to find ought after that the probes are 13mm long and good to just 780F. I just bid on another controller with a 10" ceramic probe. I'd like to stop buying controllers and just get thermocouples, buying out of frustration is getting expensive :rolleyes: I dunno if I can rig something with the lower temp probes, they are threaded for that measly 1/2", so maybe I can attach them somehow to the low temp trough and get a decent reading (and I have two chances at testing it, argh) but I need something for the high temp-4x24 ss tube ordered from Darren Ellis, which should be in next week. Still got to build the things, so I'm wide open to suggestions.
 
Your best bet to get the right/best TC for your use is to get ahold of one of the reps at Omega Engineering. A K type TC in their XC series (insulated) will run you about $22. Since you're going into salts you might want to set up a thermowell for the TC to slide into. Here's their link, give em a call.

http://www.omega.com/
 
I usually buy my stuff from Watlow through Southeast Heaters.

I use the 3/8 inch "heavy duty" stainless variant and get them extra long--I mean extra, extra long and bent at 90-degrees as show in the pic. (this is done easily by hand).
The reason I do this is that I have found a weak spot of TCs is the end of the stainless steel tube, where the wires come out. These salt pots put out a lot of heat straight up and you want to keep that delicate junction plenty clear of that environment. Doing this has extended my TC life dramatically.

http://www.bladeforums.com/forums/attachment.php?attachmentid=64178&d=1166324689
 
A thermowell is the way to go to protect your thermocouple. At work (oil refinery) all our thermocouples are in thermowells. Most of the TW are way to heavy for what we do here but basically are just stainless steel tubes that protrude as deeply as possible into the substance being measured. I plan to use an old 1/2" stainless burner tube as a a thermowell in my saltpot when I built it. The one end is a welded on rounded end with a small fuel hole I will weld shut. I can look around for some more if anyone is interested. I can get short pieces of small bore stainless steel pipe that we consider waste no problem if someone wants some. Under about a 8 to 12 inches. I am going to have to cash in a favor or 2 to get the 2' piece of 4" for the pot itself.
 
I read that thermowells throw the reading far off. Kevin Cashen mentioned there being a difference in readings, and it was Bruce Bump who mentioned that he believed he was about 100 degrees off when he placed his thermocouple inside a ceramic tube.
 
I will find out when I built mine. I will get the salt up to say 1500 with thermocouple in well and then remove the thermocouple from the well and submerge it in the salt and see what it reads. Even if there is a decrepency I will keep using the thermocouple in the well and adjust for the difference.
 
J, have you have any problems with SouthEastern?

I originally went with them because they had the "Don Fogg special" (package of PID controller, thermocouple and quencharc suppressor).

I have ordered TC's from them a couple times since and it hasn't left me happy.

The first time I waited months for a reply to phone calls/emails about getting them in the first place.

The second time they sent me the wrong TC's (I always order 2). They sent me two more and said, "Sorry, our fault, we'll make it right."

Well, they charged me for the first AND second package they sent me.

I will be talking to Omega next time around.

BTW- EXCELLENT looking salt set-up you have!!! Very nice!!! :D :thumbup:
 
When you speak with Omega, ask for the Technical Department, and DON"T use a Sales Engineer. The tech engineers know their stuff far better and can take the order for you.

BTW, thermowells function better if they're sized to your probe, not loose fitting.
 
Huh,
I've never had trouble with them, but then again, it's been a while (I tend to stock up on stuff once I know what works). They had always been helpful in the past. I hope your bad experience was a fluke, but you never know ...:(
Good luck!
 
There is no doubt the thermowells will save your thermocouplers. The low temp is not an issue at all but the high temp will chew up the inconel sheathing. I get about a year out of the high temp type "K". Normally it is a bend that is the problem, after they get so old if they get a kink or a bend I just leave it alone as strightening a corroded thermocouple invariably ends in a break. I have extended the life of them by washing them off well after use. The reason I have the issue with the deviation of the thermowell is because of all the experimentation that I do and am often taking readings specifically at different parts of samples. If a person had a very regulated and consistent setup and knew what to compensate for they should be happy with it.
 
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