Do you know if TC probe can be cut???

C Craft

C Craft

Well-Known Member
Does anyone know if a K type TC probe can be cut??? I have one that is about 10" - 12" in length and is really in the way for what I am using it for. I am wondering if it can be cut at either end. I tried a Google search but haven't found any info on the subject!

Tc-02-K-Type-Thermocouple-Probe.jpg


It is similar to the one in the pic as it has the yellow plug right at the end of TC but, it just comes to a rounded point at the other end, instead of the blunt end like the one in the pic! I bought this thing a long time ago but I never used and where I have in use now it is just too long!! If it can't be cut I will need to find a shorter one with the plug end and replace the existing one!

I am wondering if where it goes into the plug is just like a compression fitting???

Anyone got any knowledge in this area????
 
I wouldn't cut one one. I'm sure they CAN be cut but you'd probably ruin it. You definitely can't cut the non-plug end as they measure the temp right out in the last inch or less of the tip.
 
If you cut it, it's wrecked. The "wires" inside a TC probe are a specific diameter and LENGTH, to generated the correct current, which supplies the readout information. Even if you cut it and get everything back together....the current going to the readout device will be incorrect, which means the readout will display the wrong temp.
 
The diameter and length of TC wire has no bearing on the accuracy of a TC. That TC you've got is actually a SS tube with two wires inside, usually packed with a material. You can cut that anyway you wish and still make it work. "IF" you cut the tip end, you'll have to re-weld the wires together. Understand, if you cut it at the tip, the TC will still read, just won't last very long at all. "IF" you can cut it at the plug and not lose any of the packing material, and can connect to the small wires - you'd be ok... maybe {g}

The one big thing about TC is the TC wire MUST reach all the way from the welded tip, to the voltage reading device. The welded tip of a TC wire (dissimilar metals) generates a millivolt voltage depending on temperature. If copper wire is used to carry this mV signal from TC tip to the voltage reading device. The wire in a type K TC is chromel and alumel. Chromel positive relative to alumel. Chromel is an alloy made of approximately 90 percent nickel and 10 percent chromium, while Alumel is an alloy consisting of approximately 95% nickel, 2% manganese, 2% aluminium and 1% silicon. The voltage generated by the junction ranges from zero volts at 32ºF to around 40mV up somewhere around 2,000ºF. 40 millieVolts is not very much voltage.

Oh, the wires don't actually have to be welded to generate this voltage, just touching good (twisted) - but any corrosion will cause loss of signal, so welding is the general method of connecting. In industry special terminal strips are used to extend the TC wire to voltage sensing device.

OK, more than you ever wished to know about TC wire. Ed is correct about cutting that TC probe will most likely "wreck it" for practical use. Those things are so cheap on ebay or Amazon - I think I paid $2 each for the last I purchased. That is the SS tube type that are only good for temps of well less than 800ºF. For forge temps you need a size 8 or size 10 AWG solid wire TC with ceramic insulation.

Ken H>
 
OK guys I get it bad idea, just a thought!

So will be looking on Ebay for a replacement! I need one with the plug already on it so I don't have to go thru all the hassle of doing a re-wiring project. The one I got when I ordered the PID from Hell was only pictured and did not have a length. In the pic I would have guessed to be 3"-4" in length. Turned out that it needed a dime in the pic for reference, as it was only 3/4" in length. When I saw it, I just thought really,I mean really, "what is it going to be when it grows up"!

Ken you had seen it and probably realized before myself that it was going to be a problem! I had it on hand and when I saw the 3/4" probe was not long enough to go thru the fire wall I thought I would try it! Time for plan B!:biggrin:
 
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Ken how much does a probe need to stick inside the heat chamber to get an accurate reading! Anybody??
 
The temperature reading comes from only in the last inch or less of the tip so......depending on what you're using it in, that should help.
 
You're talking about heat chamber of your tempering oven? I like the probe tip (part that actually measures) to be located just over the rack holding blades. That assures the blade temp is VERY close to the controlling temp of PID. "IF" your oven has a fan circulating the air, this is less critical.

Ken H>
 
OK I hear what you are saying. However now I am more confused the ever!:les:

Ken I am talking about the tempering oven I built. You saw it, I centered the probe center from both top to bottom and front to back of the ovens chamber.

I had thought about relocating the probe from another direction but if you put the tip of the probe center of the oven, it will still put it directly in the way of the knives on the rack.

I am wondering if I need to just relocate the probe from the center of the oven to just below the top elements.

My toaster oven has two elements top and two bottom. If the probe actually measures by the temp by the last inch of two, the only way to get the probe out of the way would to be to raise it up higher, which puts it closer to the two top elements or drop it lower, which puts it closer to the bottom two elements!

Some how I have to get it out of the way of the rack and the knives sitting on it!!!!!!
 
here are some to choose from, the K type is rated to 2300F. http://www.mcmaster.com/#thermocouples/=w1bxx3
here are connectors, you just tighten and loosen the screws to install the wires http://www.mcmaster.com/#thermocouples/=w1bzdx
to shorten what you have, just trim from the end that goes to the display. the one i listed on the first line has multiple 2" long ceramic protectors so it is easy to trim to length and still have protection for the thermocouple wire.
tests at the office has shown that using short lengths of plain copper wire(less than 1 foot) to attach thermocouple to display did not change displayed temperature. with the probes we were using, difference between identical thermocouples was +/- 1 degree F whether we used copper wire or not.
scott
 
OK so if you don't now go to the well for a drink. The probe I have currently is an Omega probe so I went to their site. I spoke with a rep and tried to explain my dilemma with the oven. Elements top and bottom and I need the center open and free.

He suggested that since I didn't now which would be hotter or colder the top or the bottom to put the probe on the bottom. The the conversation that got really interesting. He said often they suggested two probes in a case like this. So I asked can two probes be tied together and get an average temp with one PID reading the two probes. He responded with absolutely, as long as the probes are of the same type TC and they have the same AWG wire!

So now I have a choose of taking the probe to the bottom of the oven or going with one top and one bottom and tying the two together, which should in theory give me a much truer reading of the tempering oven actual temp!

I am thinking I will go with two probes. My problem now is finding two about 8" in length that have a threaded ended where I can lock them off to the cabinet wall, something similar to these I can then tie the wiring together and I should be in business. My problem is I am old school and I have to go to the conversion chart to convert metric to inches. I wish we had either fully converted to metric in the states or not, at least I would know what is going on that way!:biggrin: Let see 8" is 203.3 mm, give or take a little!:what!:
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if you go to McMaster you will find about 15pages of thermocouples of all sizes, shapes and lengths. as i said, we did in house testing and found the thermocouples we were using had about the same difference in measurement regardless of length and how they were connected. you are measuring your tempering oven, main thing i would be concerned about is having the blades contained so they are not in the open when elements go on and off. +/-5degreeF temp difference is not going to change your final hardness. get a length of 2" or 3" thick wall square tubing, mount your thermocouple here, then put blades inside.
 
Scott - you are correct (as you know), a short piece of copper wire is no big deal - not enough voltage drop to worry about there. I had moved into my "industrial" mode thinking of long lengths of wire, perhaps 300 or more feet from TC to display. I have used standard terminal strips many times for TC work, even though the vendor will suggest you "need" to by his expensive TC terminals.

Cliff - that's VERY interesting about connecting two TC sensors together - did the rep happen to mention if this was series or parallel connection? Many times in industry I've used two sensors, and perhaps even three, but each of the sensors always was connected to a "black box" that would combine and average (or take best 2 of 3) for display. I'll have to try that - got a few type K TC laying around here.

For location in tempering oven, don't try to over think this thing. I wouldn't wish the sensor tip to be too close to any of the heating elements, top or bottom. I'd try to locate the tip of sensor as close as possible to blade without causing any interference with location of blades. Since your oven had elements top 'n bottom, I'd come thru the back just as you did, and have the TC tip around an inch above the blades itself.

Ken H.
 
Scott, do you think a muffler pipe is needed inside a toaster oven? For a forge, yes, I've used that..... hmmmm, a muffler pipe would help even out the heat for sure - especially if you've got several blades inside the oven.

Cliff- I don't remember, but wasn't there a small fan in that toaster oven for circulating the air?

I've got to get busy mounting a power supply in my main computer. I'm on my CNC machine box now - had a PS to go bad Sat.

Ken
 
Ken the fan motor was to cool the electrical in the controller box, PID and SSR, that was probably overkill but, someone convinced me right or wrong that PID's and SSR's created a lot of heat!

Perhaps I am over thinking all of this I need to see with the rack in the bottom slot, my fire brick that holds the blades and a max. blade about 2" thick where can I get the probe in?? I still think that is going to put it very close to the top elements!!

I thought having an oven with top and bottom elements mean a more even heat, never thought about lack of space when you squeeze all that into a small space. Oh if foresight was as good as hind sight well,................Id be a rich man and I could pay someone to worry for me!:s12137:



Ken Quote:Cliff - that's VERY interesting about connecting two TC sensors together - did the rep happen to mention if this was series or parallel connection? Many times in industry I've used two sensors, and perhaps even three, but each of the sensors always was connected to a "black box" that would combine and average (or take best 2 of 3) for display. I'll have to try that - got a few type K TC laying around here. '

OH, to answer your question he did not expound on the how to of tying two TC together! Here is a transcript of the conversation as it went down. Dang it Ken I need you in my back pocket to make me as the right questions!!!!!

Chat Transcript [Gerry] Hello, my name is Gerry, how may I help you?
[Clifton Craft] I have a steel tempering oven that uses an Omega K type thermocouple. The oven has two elements at top and two at bottom. I now have the probe dead center of the oven. However it is in the way for the steel being tempered. Would it be better to move the probe closer to the top two elements or the bottom two elements to get the probe out of the way?
[Gerry] one moment please

[Clifton Craft] I know ideally the center is going to give the truest reading but the center of the oven is where the steel sit during tempering!
[Gerry] I understand..in applications like this we suggest to place two thermocouple sensors, one at the top and the other at the bottom…
[Gerry] every oven works a little bit different..I am not sure if you know which section is colder..based on this I'd suggest to put the sensor on either top or bottom
[Clifton Craft] Can you tie two sensors together and get an accurate reading? If I were to use two sensors. I have a PID that reads temp on this TC
[Gerry] Sure you can tie two sensors as long as they are the same thermocouple type and same AWG wire
[Clifton Craft] Tying two together of the same type and same AWG wire and sending it to the PID will give me an average temp of the two probes. Is that what you are saying??
[Gerry] correct
[Clifton Craft] Gerry, that sounds like a plan. Thank you for the info. That sounds like the best solution to my problem of getting the probe out of the way!
[Clifton Craft] Now I have to find two probes the correct length for my oven.
[Gerry] sorry for the delay
[Gerry] problems with my PC

[Clifton Craft] Not a problem I am trying to look at the product selection as we speak!
[Gerry] I am sure you will find out a probe for your application
[Gerry] We have a large selection of thermocouple sensors
[Clifton Craft] Thanks for your help today!! That is pretty much all I needed. You have been very helpful
 
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i bought a small convection oven for tempering, built in fan to help keep temperature constant. i took readings so i know that the dial position that says 350f is really 361F. i guess just a tray above and below the blades will protect them from radiant heat from elements.
 
Scott - your small convection oven is a bit more than just a toaster oven? My toaster oven's t'stat would swing anywhere from 10 to 20ºF (or more). That's why I added control with PID controller. Now it holds around ±1ºF..... might swing 2 sometimes, but seldom. The wife's convection oven in the house is pretty accurate and doesn't swing much at all. Would actually work ok for tempering. I like having my own tempering oven in shop - she had a hard time understanding why I needed to "bake those knives".

Cliff, maybe just connecting 2 TC wires to the PID controller would work? Some industrial types will have two inputs for TC - maybe that's what the guy was thinking? I gotta wire up two TC and measure voltages to see what happens.

Later
 
KenH said:
Cliff, maybe just connecting 2 TC wires to the PID controller would work? Some industrial types will have two inputs for TC - maybe that's what the guy was thinking? I gotta wire up two TC and measure voltages to see what happens.

Later
Click to expand...

Ken I will be waiting for the results from that test!

For now I am going to quit having a panic attack. I am going to order one the correct length and put it in just above the top of the blade, from the back! Like you said and the rep said. This struck me as funny when he typed this. Is the following what they mean by covering your own butt from both directions??

[Clifton Craft] I know ideally the center is going to give the truest reading but the center of the oven is where the steel sit during tempering!
[Gerry] I understand..in applications like this we suggest to place two thermocouple sensors, one at the top and the other at the bottom…
[Gerry] every oven works a little bit different..I am not sure if you know which section is colder..based on this I'd suggest to put the sensor on either top or bottom

REALLY, I MEAN REALLY, the top or the bottom, well if the center is out then,................................the other logical choices would be top or bottom!
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Yep, CYA is the way tech support is taught. Like a politician - nothing absolute.

Ken H>
 
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