Jump to content

thermocouple accuracy

Recommended Posts

Hey All,

I'm working a a little home workshop playtime project...

I'm using a V570 with a V200-18-E3XB snap I/O module.

I "hand-rolled" some type T thermocouples (wires at the business end tightly twisted and soldered to create my TC junction).
Each T/C is about 30 ft long, and a direct connection with the E3XB module.

I find that the readings I get at room temp are about 8 deg F higher than I get with "real" thermometers.

I know I can build an offset into my readings, but curious where the discrepancy lies;
Does the solder (60/40) that flows through the twisted Copper/Constantan junction create an offset?
Does this fall within the expected accuracy of the E3XB module?
Or is it something else?

Anyone have any input on this matter?


tc junction.PNG


Link to comment
Share on other sites

  • MVP 2023

My current arrangement with John is that I compensate him with Walmart gift cards.  A nice big image like that is going to cost me plenty  😃

The solder in a type T thermocouple may cause an issue if it's getting in between the two metals.  And it probably is.

Stick the sensor in two known temperature sources - crushed ice in water (AKA a 32 deg F Ice Bath) and boiling water.  Water boiling point decreases 1 deg F per 500 feet of altitude, so in our region it should read 211 deg F.

If the error is the same it's an offset.  If it changes then you have a mathematical correction factor, which may or may not be linear.

Or you could weld the end using a 120V line cord jammed into a carbon block with a 100W light bulb as a current limiter like the do in the Emerson Motors lab.   It works great.


If you shock yourself I will disavow any knowledge of your actions.




@Flex727 - for additional revenue, consider this experience I had with the Malwarebytes forum-



He was VERY helpful with my problem.  Yes, I did send him money.



Joe T.

Link to comment
Share on other sites

OH MY.... I didn't catch that shameless inclusion of the JTA sticker... 🙄

But Joe, I can give you my paypal info if that's easier than the WalMart cards.... 🤑

I think I'll play around with the MIG method using an argon shield as I have that available in my shop....



Link to comment
Share on other sites

  • MVP 2023
15 hours ago, Joe Tauser said:

My current arrangement with John is that I compensate him with Walmart gift cards.

Sounds good, but I'd rather save up until I have enough for a new V700.

15 hours ago, Joe Tauser said:

for additional revenue, consider this experience I had with the Malwarebytes forum

I wonder if Unitronics has a policy about this?

The Paypal issues aside, a disclaimer like that at the end of every post would be very helpful to let users know that most of us are volunteers and not Unitronics employees. I need to check to see if that can be automated with this forum software.

Link to comment
Share on other sites

I think this should be a message on the header of all posts.

For example I get a default message when I post stating the following "Your content will need to be approved by a moderator".

Many new posters get frustrated when their post is not posted, read or solved immediately, not realizing that this is a voluntary forum.

When people try to post there should be a message advising them of this and also if they would like to also send to the official UNITRONICS support.

It would be easy for the forum designers to include this than everyone needing to set up their individual messages.

Link to comment
Share on other sites

Well, as a follow up...

I did set up a T/C welder (as suggested in Kratmel's post) with a tungsten in a modified tip in my MIG with an argon gas shield, and welded the T/C junction instead of soldering.

But, in a side by side comparison, the readings from the welded junction and the soldered junction were almost identical, so much for the theory that the solder flow induced an offset the reading (which is a relief in one way as I have been doing soldered junctions for years).

And since my mentor, Joe T, has said many times, "empirical data tells all"..., I will build an offset into my code to make my readings closer to being correct...


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...