Thermocouple or thermocouple wire source?

Where did you DIYers who use thermocouples or thermocouple wire get yours? I find that shipping tends to be really expensive on such a little thing. Better yet -- any of you have a coil of thermocouple wire sitting around that you want to snip an end off and throw in an envelope? I'd happily paypal ya a couple of bucks....

What type are you looking for? I'm back on the nightshifts tomorrow, but I may be able to root some up. Can get some in 9 days for sure when I'm back on the days.

Awesome! I can use almost any type: J, L, K, T, E or N should all work. I'm using (or at least trying to use) a Love 16120 controller to modulate a fermentation fridge. Thanks!

Have you looked on Ebay for thermocouples yet?, extending thermocouple leads with dissimilar metal wiring can create some interesting results. Best to look for a thermocouple with leads long enough to reach controller without junctions unless you want to invest in plugs or terminal blocks for the type of thermocouple you are using.

kladue said:

Have you looked on Ebay for thermocouples yet?, extending thermocouple leads with dissimilar metal wiring can create some interesting results. Best to look for a thermocouple with leads long enough to reach controller without junctions unless you want to invest in plugs or terminal blocks for the type of thermocouple you are using.

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Not only that, but you should not cut the leads on any thermocouple you do get. They are calibrated with that length of wire, so any changes will throw off the reading.

JoeRags said:

Not only that, but you should not cut the leads on any thermocouple you do get. They are calibrated with that length of wire, so any changes will throw off the reading.

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Better re-check your theory on that one.

mr x said:

Better re-check your theory on that one.

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care to enlighten me?

You can cut thermocouples. They are usually sold on large rolls that you cut to what ever size you need.

Guess you learn something new every day!

I've only purchased TC's for automotive pyrometers. They typically advise against shortening of the wire for these applications.

That's looks like a specialized application. I've never heard of one of those, but in that case, I would say it's best to follow the manufacturer's instructions. Generally speaking, standard type thermocouple wire comes in massive rolls (to industrial users) and you cut is as you see fit.

Hear me out for a second though... Am I wrong to think that a very long run of wire on a thermocouple can affect the reading? There's obviously more resistance per foot of wire added to the TC. Are they calibrated once install is completed?

Pyrometers are used to measure exhaust gas temperature on turbo applications. This is a critical reading for diesels pushing high HP and hauling big loads. The TC is usually placed in the exhaust manifold between the turbo and the engine

There are limits on length. Around 100 ft is a ballpark I've seen, but it really varies with the gauge of wire and some other factors. I have never been in a situation where shortening the wire causes problems, but it may be possible that too short a wire could cause problems. The wires themselves are built to a standard that has a min/max temp and accuracy, so they really aren't calibrated as such. Most transmitters can be calibrated, but I have never done this with a TC. If I didn't think the reading was good, I would either toss the wire or the sensing instrument.

Thermocouples can be extended 200+ feet with same type thermocouple wire as they generate a voltage instead of changing resistance. The main thing to remember with thermocouples is they generate a voltage across dissimilar metal junctions so you need to use plugs or junction blocks built for the type of thermocouple wire used, else every junction will throw off the readings.

Yeah. What they said.

I was under the impression that with relatively short runs of TC wire (under they 100 foot mark was what I'd heard), length of wire didn't change the output. Glad to hear that confirmed, thanks mr x and kladue.

I spaced on the wire type issue, though. I was planning on using the jumper wire I've got hanging out in my toolbox to extend it to the length that I needed, and hadn't even considered that I'd be generating additional thermocouple junctions that way. D'oh! So, mr x, it looks like I'm looking for ~18 inches of tc wire after all.

This brings up an interesting question, though (well, interesting to me, anyway.) The Love controller I'll be using can use essentially any type of thermocouple; you just have to tell it what you're using. But each of them would be attached to the process controller at the same terminals (copper, maybe?) Isn't that going to create two additional thermocouple junctions, one at each terminal - TC lead connection? Or is that compensated for by the circuitry of the controller, and that's why it's important to set the type correctly in the configuration menus? Apologies if it's a dumb question.

IIRC the controller junction is temperature sensed and compensated that way in good quality instruments.

BTW, I have about 5 feet of J type here. I'll see what's at work. I think T type might be better.

Ah, that makes sense.

I think you're right that type T might be better.

Try www.mcmaster.com for a source.

Thermocouples I know of are only accurate to +- 2 degrees Celcius, whatever that is in F ( over 4 degrees, I think ).
I have had a K type. It has not been a consistent error that can be adjusted for.

I prefer to read the mash more accurately, and every source I know of states that this difference in mash temperature makes a different beer.
Repeatability is very difficult.
So:
I now use an RTD.

These are accurate to about .4 degreees C.

No more difficult to use than a thermocouple.
About the same price.

Why use a thermocouple in preference?

Yuri -- I did check out McMaster, and it was way too expensive for what I needed. Thanks for the suggestion, though.

Yorg -- Actually I believe a type T should be accurate to within .5 degrees C at fermentation temps (which is what I'm monitoring, not mash temps).

D'oh! I just re-checked McMaster after writing that last post, and they do sell TC wire after all. All I saw before when I looked were pre-fabbed probes for ~$20 or more.

Is there any way to tell how much shipping will be before you place your order? I don't see any info at all on their site about that, even when I've got my item in my basket and ready to check out.

I have some type K, no T. It's what we use because of the high temp range (good for boilers and kilns). Anything that doesn't require high temp gets RTDs.

http://tinypic.com/view.php?pic=8ak51j7&s=1

I have some K type wire, How much do U need? And I live close to U, in Coldwater

e lo said:

Is there any way to tell how much shipping will be before you place your order? I don't see any info at all on their site about that, even when I've got my item in my basket and ready to check out.

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Unfortunately, no. The lack of a shipping quote at McMaster is a common complaint. All of my orders have been shipped via UPS ground, and the shipping charges are usually pretty reasonable.