I have K-Type Thermocouple element, but the problem is that I have J-type cable to connect it to the controller, the cable run will be around 300 feet, and the process temperature will be within the specified range of the K-type and J-type, So what worse could happened if I run the J-type cable instead of the K-type cable.

Forget to mention that the purpose of the thermocouple is only to verify that there is heat or not and it not meant to give exact and accurate temperature reading.

Best Regards,
Mohammad M.

 

For what you are describing, you might as well run copper cable! The temperature reported by the thermocouple detector (analog input) will be the measured temperature minus the temperature at the point where you transition from type K to copper. As long as the temperature at this point is substantially less than the measured temperature you should be OK.

If you use type J cable, you will have a chromel-iron junction and an alumel-constantan junction at the transition point, plus an iron contstantan junction at the thermocouple detector (which is looking for a chromel alumel junction at that point). I don't know what you will end up with, but I think it will be a greater error than using copper. The only reason to use type J cable would be if you eventually plan to replace the type K thermocouple with a type J thermocouple.

 

I'm so glad to read the original post. I bookmarked it for future reference.

A couple days ago on this forum I listed 10 or so reasons temperatures in flow stream could vary upstream from downstream, all of which I've encountered over the years.

I had wrong extension wire on my full list but culled it from my response for no reason in particular (full list has about 50 reasons).

It amazes me to uncover evidence that J extension wire would deliberately be mixed with a K couple. Yeah, if it's connected with the correct polarity, the circuit will show a temp increase or decrease, but my old bones can only ask, why?

I mean, doing it the right way, using a J couple with the installed J wire, could cost what, maybe $10 US? And then 2 or 5 years from now, whenever, when people are pulling their hair trying to figure out why the electronic temperature doesn't match the local bimet by 30°, they'll have to call me or someone like me, pay big bucks, T&M & travel, for the problem to be tracked down. Shame, when it could have been done right the first time for $10. But stuff like this helps pay the rent. So do it.

David

 

The main problem that I see is not in whether or not mixing lead wire (J or K) will provide an indication of temperature. It will likely do this.

However, someone down the road is going to say, " Oh, we have this J thermocouple on that process we can retransmit that signal over there and then you can use it for . . . .

Do you begin to see the problem? If you are going to measure it in a plant environment, doing it right is always best.

Bruce