Tet-612 thermocouple help!

Hey all, I have set my pid farther away from my brewing area in anticipation of a future upgrade to something like a touch screen POS kinda thing. In order to make this work I had to extend the thermocouple wires. I bought type k male and female plugs and thermocouple wire and have it running out to the PId which is about an additional three to four feet away from the kettle. Trouble is, now my sensor is way off. Polarity is fine, but during a test run last weekend the temps were approximately 40 degrees F too low. Better than too high; however quite unacceptable.

Today I had time to try to recalibrate the sensors and set out to do this. I took my first temp reading at 42 F ambient temp (my garage is chilly) and while I was getting things ready to fill the kettle and find the offset in temps while at boil I noticed that my PID was reading higher by a few degrees. A I watched I noticed that it kept climbing. Temp difference initially was 7 degrees, then it climbed to 20 degrees over the next ten minutes of so. At this point I shut the PD off and came in to post this. Any touts on what is going on here? How can I calibrate a system that is not static?

It sounds like a bad connection somewhere. If a wire is not making good contact the readings can go all over the place. Maybe check the ohms on each wire from pid all the way to the sensor and see if one has different resistance.

extending thermocouple wires is never a good solution, small difference in resistance can dramatically affect the reading, as can heat on the cold junction of the thermocouple, using an rtd is a better choice for this problem, especially since they arent really affected by splicing wire/solder connections etc

Will crap. I don't think that the tet612 allows for rtd sensors. I left the PID on for about two hours tonight and it seemed to max out at about 30 degrees over ambient, but that was not with normal brewing air temps or heat from brew kettles changing localized temps either......

Mike

I wonder if I could source a k thermocouple with a six to eight foot long cord... This would eliminate the junctions and spliced cables while still allowing me to keep my controls where they are.

Yes, likely you could from an outfit like Omega.

However, using the extensions shouldn't give you that kind of error unless there is something wrong in the chain. I use extensions with type K thermocouples on a fairly regular basis and don't have that problem.

Just a few minutes ago I tried first one, then two, 10-ft extensions on top of the 60 inches or so on the probe and the results were the same to the 1/10 degree.

Hate to ask but are you sure you wired the plugs and the cable properly, yellow to positive and red to negative? Has to be that way from start to finish though all connections and extensions.

just so you know the tet 612 can handle rtd sensors, and generally these are better than thermocouples in most instances. but if nothing else I would really look at your thermocouple wire that you used for an extension, was it actually thermocouple wire, or something you had laying around.

The thermocouple wire we have in the lab I work in is two different metals

I did purchase k thermocouple extension wire specifically for this purpose. I'll have to check out the wires this weekend. I do know that I tried hard to make sure that the wires were the same throughout the new extensions, however I remember on our test brew day we had to reverse the wires from my thermocouple into the jack because we were getting readings that were opposite of expected (going down as heat was applied to the system) and initially quite high.

I think it is not enough just to match up (+) and (-), I believe you also have to use the correct color of the lead wires for (+) and (-). Red wires to (-) and yellow wires to (+) all the way through.

I had time yesterday so I took the brewery apart and checked all my thermocouple connections. Everything was wired correctly and snugly. Just for the sake of science, and because I had no idea what else to do, I switched the wires, with red now going to positive rather than negative, and the thing started working! Readings were stable, and just a few degrees low, which I corrected for in the pid. Looks like we're back in business!

Huh? Very strange. Guess the main thing is that it apparently works now.