MCM Electrronics: type K beaded thermocouple w/mini connector, $7.56

[Tex]

This is what I use with my Tenma 72-7712 data logging thermometer.

Buy them by the bunch - save on S&H.

[ecc]

I would use a type K stainless steel clad, grounded, 3mm or 6mm TJ36 type probe from Omega inside a roaster.  

You can gently bend this probe to get it stay where you want, the stainless steel won't degrade into anything nasty and makes it easy to clean.

A little more expensive at $45, but is stable, accurate, and will last a long time.

[Tex]

I would use a type K stainless steel clad, grounded, 3mm or 6mm TJ36 type probe from Omega inside a roaster.  

You can gently bend this probe to get it stay where you want, the stainless steel won't degrade into anything nasty and makes it easy to clean.

A little more expensive at $45, but is stable, accurate, and will last a long time.

3 or 6 mm?

Hmmm let's see, that's ~1/8" & 1/4" right?

Even if it's grounded, those will have too slow a response.  Try the exposed tip if you must use a probe.

And there's nothing in the t/c's that'll degrade into anything nasty. If you're worried about the Teflon coating on the wires, it has a melting point of 342°C.

[Tex]

What's the max temp for these?  I'm looking to add one to my roaster which probably sees about five hundred degrees Fahrenheit max.

And do you want some Omega T thermocouples in trade?  I've got a few extra.

I've got plenty of type T t/c's but thanks. The type K t/c optimum operating range is well within the roast temp range.

[randytsuch]

What's the max temp for these?  I'm looking to add one to my roaster which probably sees about five hundred degrees Fahrenheit max.

And do you want some Omega T thermocouples in trade?  I've got a few extra.

I just used a bead type K with fiberglass insulation.  I don't know the temp rating, but it has seen over 500 degrees, and it is fine.

BTW, the last few cheap Chinese bead TC's I bought from ebay just had the ends twisted together.  For most applications it works fine, but sometimes it is nice to have a real TC with a beaded end.

Randy

[ecc]

I've had the sheath on the fiberglass beaded tc's discolor and melt in an iroast.  Once they get crudded up they aren't as accurate, and cleaning them with any vigor risks the weld.  The stainless steel clad probe does not lag any more than a beaded in this application, the larger diameter improving the stability of the readings and much easier to get it where it needs to be.

I like to try to find things rated for food contact when possible, perhaps unnecessarily.

On a side note, the DuPont website has this note:
DuPont non-stick cookware may produce fumes at significantly higher temperatures, greater than 500°F (260°C).
http://www2.dupont.com/Teflon/en_US/keyword/fumes.html

The are talking about thin layers of teflon coating, (who knows what the properties of the sheathing are, it is not pure teflon) but this seems awfully close to roaster temps.

[Tex]

I've had the sheath on the fiberglass beaded tc's discolor and melt in an iroast.  Once they get crudded up they aren't as accurate, and cleaning them with any vigor risks the weld.  The stainless steel clad probe does not lag any more than a beaded in this application, the larger diameter improving the stability of the readings and much easier to get it where it needs to be.

I like to try to find things rated for food contact when possible, perhaps unnecessarily.

On a side note, the DuPont website has this note:
DuPont non-stick cookware may produce fumes at significantly higher temperatures, greater than 500°F (260°C).
http://www2.dupont.com/Teflon/en_US/keyword/fumes.html

The are talking about thin layers of teflon coating, (who knows what the properties of the sheathing are, it is not pure teflon) but this seems awfully close to roaster temps.

Wow, that's some iroast you used! According to Omega, "...fiberglass leads are rated to 900F".

I've used them in the Sonofresco, threading them under the roast chamber, which put them just above the open flames and never had one damaged. Maybe you're using substandard parts from questionable suppliers??

[ecc]

It was this one.  I may still have it around somewhere.

http://www.sweetmarias.com/sweetmarias/coffee-roasters/roasting-supplies/replacement-k-type-thermocouple-for-digital-thermometer.html

[Tex]

Tex,

I'm interested in three if these, if your selling them.  Let me know how to arrange this.

BTW, I use Kapton tape in the roaster to tape down my thermocouples.  The type T's work fine in my PID, but I need type Ks for my roast logger inputs and voltmeter.

Thanks.

I'm not selling these, just pointing them out. How's the adhesive used in the Kapton tape?

I just have my t/c lead bent to keep the tip buried in the bean mass of my UFO/CO roaster. I had the probe in the bottom of my TurboCrazy, held in place with a dab of hi-temp silicone.

UFO-CO thermocouple placement

[ecc]

I couldn't find the damaged one, must have actually thrown something out.  In the process, I did find two more in good condition, one unused.  I will throw them in the mail to you Chris, the ones I have won't need replaced for quite a while.

[Tex]

It was this one.  I may still have it around somewhere.

http://www.sweetmarias.com/sweetmarias/coffee-roasters/roasting-supplies/replacement-k-type-thermocouple-for-digital-thermometer.html

They're probably getting their t/c's from the same Chinese factory that makes their thermometer. And I'm not too sure about the blue sheathing, which looks like some kind of shrink tubing? If that's what it is, it will melt as most shrink tubing has a flash point of ~200°C..

I do know that I've never had a problem with Omega t/c insulation melting, either fiberglass or PFA.

[ecc]

It took a while to deteriorate.  More likely a combination of abrasion, some fiber melting together, and extrapolation on my part.  It must have looked pretty bad for me to throw it away, though...

Here is the Omega data sheet for tc insulation, couldn't seem to find it before.
http://www.omega.com/techref/wireinsulation.html

[ecc]

yakster posts always make me want to post more pics, had to swipe my camera back for a second but...

My tc collection: (and an unintentional illy advertisement)
left: 2 sm tcs's (used one also in the insert)
top: submersible tc
middle: general purpose tc
right: heavy duty roaster tc

[Tex]

It took a while to deteriorate.  More likely a combination of abrasion, some fiber melting together, and extrapolation on my part.  It must have looked pretty bad for me to throw it away, though...

Here is the Omega data sheet for tc insulation, couldn't seem to find it before.
http://www.omega.com/techref/wireinsulation.html

That's what I was looking for - thanks!! The insulation Omega puts on t/c's is TT (PF) & GG (hi-temp glass). Since my roasts never intentionally  get over 500°F there's never been a problem.

[Tex]

Todd,

Thanks, I appreciate it.  Let me know if you need any type T thermocouples or if there's anything else I can throw your way.

Tex, sorry, I thought you were selling these.  I've attached a picture of my taped down thermocouple wire in my Behmor.  It's really high temp 3M tape used mostly in printed circuit board work.

As far as the blue sheathing on the end, I remember some discussion on the Sweet Maria's home roaster's email list about this melting and that it should be removed before use.

I tend to over-engineer things, so I'd probably drill a hole in the back and use an exposed tip probe & a compression fitting to hold it in place. Then I'd see something like what you did and wonder why I went to so much trouble to do something so simple? I preach the KISS Principle, but seldom apply it to myself!