DIY Thermocouple for PID

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EarthBound

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Here's the idea:

Buy some type K thermocouple lead wire.
Cut to the desired length.
Connect one end to a PID.
Strip 1/8" on the other end.
Twist the ends together.
Now you have yourself thermocouple.
Make a thermowell out of some copper tubing, a copper cap, and a compression fitting.

Let me know whatcha think.
 
Here's the idea:

Buy some type K thermocouple lead wire.
Cut to the desired length.
Connect one end to a PID.
Strip 1/8" on the other end.
Twist the ends together.
Now you have yourself thermocouple.
Make a thermowell out of some copper tubing, a copper cap, and a compression fitting.

Let me know whatcha think.

If you make sure you have the right kind of wire, it should work fine.

There is "extension grade" wiring, which is what you see most often, and is meant for extending the leads from a probe to the instrument measuring temps.

Then there is "thermocouple grade" wiring that you can make thermocouples out of.

The main (only?) difference in the two is the temp rating. Extension grade wire is not meant to handle high temps, but thermocouple grade wiring is.


Oh... and you need to make sure that the wires do not touch the thermowell, because the introduction of another metal will mess things up.
 
For $10 or less on Ebay you can find SS jacketed type K thermocouples, the roll your own method is likely to cost more. One problem you will encounter with a twisted junction is the corrosion that happens on the wire surface will probably cause problems later, all commercially produced thermocouples usually have welded junctions.
 
It works great. I have done it for over 3 years. I made a thermowell out of copper tubing. Pinched one end and dropped some solder in the open end. I then heated the pinched end to seal it. I then drilled out a compression fitting and put the open end of the tubing into the fitting. Done. The wire does, indeed, touch the copper thermowell and it has no effect on temperature measurement.
 
It works great. I have done it for over 3 years. I made a thermowell out of copper tubing. Pinched one end and dropped some solder in the open end. I then heated the pinched end to seal it. I then drilled out a compression fitting and put the open end of the tubing into the fitting. Done. The wire does, indeed, touch the copper thermowell and it has no effect on temperature measurement.
Correct, grounded type;)

There are three junction types, grounded, ungrounded or exposed.

Grounded: The thermocouple wires are physically attached to the probe wall.

Ungrounded:The thermocouple junction is detached from the probe wall.
Ungrounded offers electrical isolation.
Exposed: The thermocouple junction is exposed to the surrounding environment, limited in use to dry, noncorrosive applications.

In my set-up I use ungrounded thermocouples.

Cheers,
ClaudiusB
 
I have no idea. It *looks* like the right stuff, but I am not the seller, so I can't say for certain.

It seems that the only difference between the two different types of wire is temperature rating. This seller's "lead" wire and extension wire have the same specs: a temperature range of up to 752 degrees F. Even if it is extension wire, I can still create a junction, and therefore a thermocouple, since there is no worries about temperature, right?
 
I have an omega pid. I don't know if my thermocouple is grounded or ungrounded. I would say the junction is exposed as it is just the two strands of wire twisted together. I think my thermocouple wire is coated with PVC. I use something similar to this:
http://cgi.ebay.com/Omega-Thermocou...ultDomain_0&hash=item2a0fbdb477#ht_2886wt_905
Obviously, you don't need 500 feet but maybe you can find a seller that is selling something similar in shorter lengths.
I think this would work as well. It is teflon-coated and tolerates higher temps.
http://cgi.ebay.com/ws/eBayISAPI.dl...49374&ssPageName=STRK:MEWAX:IT#ht_2188wt_1139
 
I have an omega pid. I don't know if my thermocouple is grounded or ungrounded. I would say the junction is exposed as it is just the two strands of wire twisted together. I think my thermocouple wire is coated with PVC. I use something similar to this:
http://cgi.ebay.com/Omega-Thermocou...ultDomain_0&hash=item2a0fbdb477#ht_2886wt_905
Obviously, you don't need 500 feet but maybe you can find a seller that is selling something similar in shorter lengths.
I think this would work as well. It is teflon-coated and tolerates higher temps.
http://cgi.ebay.com/ws/eBayISAPI.dl...49374&ssPageName=STRK:MEWAX:IT#ht_2188wt_1139

So you are using extension wire and have experienced no problems doing so?

Do you use (or do you suggest that I use) thermal paste/grease to provide better heat transfer from the thermowell to the junction?
 
I plan on implementing this idea soon. I plan on trying it with TC wire and extension wire to test the theory. I'll post the results on here when I get around to it. I fingered this idea would've caught more attention than it did, but that's what I get for fingering.
 
Don't use extension wire for the probe end. We routinely build our own thermocouples at work for low and high temp applications and have never had any issues. I would recommend after twisting the ends together to put a bead of silver solder on the wires.

Don't know if I can post links but here is some good info from Omega.
http://www.omega.com/prodinfo/thermocouplewire.html
 
Don't use extension wire for the probe end. We routinely build our own thermocouples at work for low and high temp applications and have never had any issues. I would recommend after twisting the ends together to put a bead of silver solder on the wires.

Don't know if I can post links but here is some good info from Omega.
http://www.omega.com/prodinfo/thermocouplewire.html

I heard the same thing from the guys at my work, so I won't be testing to see if extension wire will work. I'd like to test it, just for schnitz and giggles... but I do not have any extension wire on hand, nor will I bother wasting the money on some.

Earthbound...I'm also interested in seeing those results!

If I can DIY my thermocouples...I want in! haha!

From what I've seen and heard, I have concluded that you can easily DIY your TCs. I'm pretty excited, too, because of how easy it is. I already have the thermowells made and some J-type and K-type TC wire.

I'll be saving about $100! :ban:

I think that making a TC is a pretty cool idea because, in this application, it's really a low-tech product... not like I'm trying to make a thermapen.
 
Tease, after all that buildup :drunk:.

I'm still wondering the answer to Walker's question:

Sorry to disappoint buddy, but RTDs are really the way to go!

The explanation to his question was that I should've clarified exactly what I was saving money on. I wasn't saving money just on the TC junctions. I was saving money on the entire setup because I can get stuff for free: TC wire, TC junctions, and thermowells. The money saved depends on what source your comparing the parts to. If I was going to buy all the stuff from Auber (which I should, since I bought PIDs from them), then I was going to spend a lot more money than if I bought them from eBay, especially if I bought their good-quality stuff, with quick disconnects and all that. I guess I shouldn't have put a $ figure on it since it made people latch onto a # instead of the concept I was trying to get across (which is saving money) I should've just said I was happy to be saving money. Also, they're not $1 eBay. That was an auction. Also, I would not have bought cheap crappy junctions on eBay anyway. I would've bought TC wire and made the junctions myself as I described above.

Long explanation, huh? Now you see why I didn't bother answering that question at first: laziness...

good luck maintaining a steady calibration.....

What do you mean by that? Are you trying to say that RTDs do not maintain a steady calibration? Or are you trying to say that TCs do not maintain a steady calibration?
 
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