how to not melt a temp probe?

J.Marsillo

J.Marsillo

Joined
Nov 8, 2000
Messages
1,255
As usual i was side tracking today and tried to put a temp probe in the forge.I have the multi meter in this picture with the type "k" probe,wont this thing melt?:confused: is the wire a consumable thing?
otc.jpg
 
That one probably will - the plastic (might be PTFE) sheath will give up first, then the thermocouple junction will start to oxidise...

I use mineral insulated, inconel sheathed K-type thermocouples - good to 1300C (last time I checked the forge with one, it hit 1300 and kept rising, so I pulled it before I melted the inconel...)

I get mine from http://rswww.com in the UK, but googling found loads of US suppliers.

HTH

Peter
 
stick the K wire down some 1/8" ss tubeing, peel a 1/4" or so of the K wire and crimp the end of the tube shut.

My buddy does foundry work with Aluminum and thats what he uses.
 
I drilled a little hole in the top of my forge and just stuck the bead wire-type probe down into the forge. The little guy was bright red, but was reading temps up to 2000 F. I recently bought a sheilded hand-probe from Omega but haven't got to try it out yet.
 
I met him yesterday and mentioned the dangers of overheating blade tips . I never thought of warning about overheating thermocouple tips !!
 
HI,
I got a graphite insulating tube off of Ebay, about $10.00 plus the shipping and have yet to burn it up. Someone told me that you could use that, ceramic, or a platinum "thermo-well" to insulate the actual probe from the oxidising atmosphere in the forge. I have yet to find a ceramic one and I'm cringing at the very thought of pricing the platinum... :eek:
The only problem I find in all that is that it seems like the pyrometer is going to read the temp inside the forge, NOT necessarily the temp of the steel you have in the forge. I was hoping to be able to tell the temp of the work piece with my little set-up. Is my logic flawed in some way, or can I still get a pretty accurate read on my steel?
Thanks for any help...

Randall
 
as long as you're getting even heat, your work piece will become the same temp as the inside of the forge.
 
I was wondering, can you put a thermocouple on any good multi-meter and use it instead of a pyrometer??
 
rocketmann said:
I was wondering, can you put a thermocouple on any good multi-meter and use it instead of a pyrometer??
Click to expand...

This is a good question. Since I have a nice Fluke, this would save me from getting a digital Omega. Can you hook a K-thermocouple to a multi-meter? If so, how do you read it? What do you look for to know what the temperature is?

Paging Fitzo. . .assistance needed in Shop Talk. . .:D
 
Fox said:
.....Paging Fitzo. . .assistance needed in Shop Talk. . .:D
Click to expand...

fitzo "electro-dumb"! :D Need PSO Phil, howiesatwork, damneng Jim, or Darren Ellis to tell us about this.

It's measuring a change in voltage. "Type K" is a specification that should have a mathematical realtionship such that you could take a multimeter reading, do a calculation, and come up with a temp. I would think a digi-thermometer doesn't do much more than provide the proper plug and have a chip with the conversion algorithm built in on a multimeter.

I'm'a don't know no more den dat. Sorry.:o

Edited to add: it's a non-linear relationship. Google "thermocouple theory" and a link pops up with a formula that makes the purchase of a dedicated meter much more attractive. LOL
 
A lot of multimeters have the capability to measure thermocouples.
Just make sure it will have a place to plug in a K thermocouple, though.
A regular old meter will not do the job, as the voltages generated by a TC are real small, and not a linear funtion as mentioned by Mike.
Myself, I'd rather use a controller to measure, as you can also use it on kilns to control temp.
The more massive the thermocouple, the more steady the readings will be...
 
Not to sound like a cheap'o but it reads up to 2000 deg. could i just coat the wire with satanite? I already melted the plastic off.

Btw thanks mete for the insight :) AND the sweet saw blade, i cut out a blade today and it made nice sparks :cool:
 
It wouldn't hurt it, and it would give it some mass.
Just don't believe what it says until the satanite has dried out...
 
Fitzo and Howie

You are right about the thermocouple putting out very low voltages and that the relationship betweent the voltage and the temperature is non-linear. There is typically either a dedicated circuit that amplifies and linearizes the thermocouple voltage or the microprocessor in the meter does a calculation to get the same effect.

For any meter that you are considering, check the temperature range that any meter is capable of reading. Many of them may not go high enough for your type of application.


Fox

Check the manual for the meter that you have. Some meters have direct connections for the thermocouple.

The Fluke models that I have used at work (model 77 and 87) do not take a direct connection from the thermocouple. There is a temperature module (80TK, -50 to +1000 degrees C, $85 list price)that plugs into the meter. The meter is set on the mV range. The thermocouple wire plugs into the module. The module puts out a voltage that corresponds to the temperature (1mV = 1 degree). This module would probably work with other meters that have the same plug spacing as the Flukes.

Only the Fluke models 187 and 189 take a direct connection to a thermocouple (using an adapter). They are also the only models capable of reading temperatures high enough for heat treating (-200 to +1350 degrees C). The list price for these two are up over $400.

Phil
 
Thanks, guys. That is some good information.

PSO, I have an older 73, but it looks like the new 77III on the Fluke site. I have probably had mine for 10 - 15 years. Given that I am looking for something to verify the accuracy of my Evenheat, I wonder if something like this might be a better choice? You know, the right tool for the job. I was thinking of getting a K type thermocouple with the long probe.

Fitzo, I think you once told me you used an Omega with a long probed K and that you drilled a small hole in your oven and packed it with Kao wool, or something like that?
 
Fox said:
Fitzo, I think you once told me you used an Omega with a long probed K and that you drilled a small hole in your oven and packed it with Kao wool, or something like that?
Click to expand...

That is correct, Fox. I use a secondary probe/meter to verify the temps in the furnaces. My old Paragon already had a couple holes, and, yes, I insert the probe and pack around it with a kaowool plug. The Evenheat, I drilled holes so I could place the probe close by the blades.

I use 18" Inconel-sheathed probes from Omega, 1/4" diameter for the furnaces, and 3/8" dia. for the forge. I now have a ceramic "condom" for the probe in the forge to improve its lifetime, also from Omega. Personally, I wouldn't bother with stainless probes again; I trashed them in no time in the forge.
 
I just got one of these inconel-sheathed probles in 1/4x12 and it is monster --
 
;)
fitzo said:
fitzo "electro-dumb"! :D Need PSO Phil, howiesatwork, damneng Jim, or Darren Ellis to tell us about this.

It's measuring a change in voltage. "Type K" is a specification that should have a mathematical realtionship such that you could take a multimeter reading, do a calculation, and come up with a temp. I would think a digi-thermometer doesn't do much more than provide the proper plug and have a chip with the conversion algorithm built in on a multimeter.

I'm'a don't know no more den dat. Sorry.:o

Edited to add: it's a non-linear relationship. Google "thermocouple theory" and a link pops up with a formula that makes the purchase of a dedicated meter much more attractive. LOL
Click to expand...


I could write several hundred words, but I'll just post a link and let anyone interested to to Omega.com and read it for themselves. http://www.omega.com/thermocouples.html

Jim Arbuckle
 
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