jld612 not sensing right temp and tried error coefficient

[biacofano]

I am working on a small brewery with three pots that need precise temperature. I am using a type K thermocouple in each pot submerged in liquid, and the each go to separate jld612 controllers. The problem is when I'm heating the pot the temperature reading goes up exponentially faster than the actual temperature. I brought water in each pot to a boil and set the error coefficient so the temp controller read 212. I did cut and extend each thermocouple wire, but I used some kind of thermocouple wire (a friend had) soldered on then to the temp controller.
I'm wondering if my readings are off due to the wrong type of wire.
Any help would be much appreciated.
Thanks.

[richiem]

I'm pretty sure that using the extra -- and wrong -- wire is the issue. I would recommend using Pt100 sensors -- they are relatively inexpensive and can have pretty long lead wires; and the wires can be lengthened as needed using ordinary copper wire without losing a lot of accuracy. I would extend the Pt100 wires using 18-gauge or larger (smaller gauge number) copper wire to keep wire resistance fairly low. You can buy insulated wire with various colors of insulation at most auto supply stores -- they usually have 16 gauge wire, and that's even better. Solder and insulate the connections -- I use heatshrink tubing for insulation.

Most Pt100 sensors have three wires, so pay careful attention to the color coding of the wires. And a nice aspect of using the Pt100 sensors is that you can have temps set to 0.1 degree and expect to get close to that resolution of the actual heat -- my hot tub of 250 gallons stays within about 0.2 degrees when just sitting there with the cover closed.