Thermocouple Frustration

I'm hoping some of you folks more familiar with the electric side of brewing can help me out.

In January I built a new system that incorporated a RIMS tube controlled by a PID and a thermocouple installed in the MLT. The first few batches went very well. And then on the third batch, I started getting random temp readings. It would suddenly drop ten or twenty degrees (instantly), but if I moved or even just touched the thermocouple wire it would go back to the accurate reading.

I assumed I'd messed up the wire by twisting it too much when removing it for cleaning, so instead of tracking down the issue, I bought a whole new thermocouple. Same thing, worked the first time, then started getting all wonky. Since I still had to unscrew the thermocouple from the MLT to dump it out, I assumed I'd done the same thing.

So...I replaced the whole thing again, this time with a disconnect for the Thermocouple wire so i would never have to worry about twisting the wire again. The very first brew, and I had the same issues.

Am I looking at a bad PID? Or is there some other issue I'm just clueless about?

I'm very close to insulating the MLT (should do that anyway) and scrapping the RIMS set-up.

How are you recirculating in your MLT? You could be experiencing channeling issues in your grain bed. Pics would be helpful. I use a HERMS method and found a way to put my RTD in a thermowell into the return line and find it very consistent.

pics always help

Definitely a wiring issue. Check any connectors you have in there.

thermocouples work by generating a small voltage at the sensor, which is proportional to temperature being measured.

if something interferes with this voltage it will throw off the reading. getting the wires wet could do it, as could a poor connection somewhere. did you solder and heatshrink all connections?

passedpawn said:

Definitely a wiring issue. Check any connectors you have in there.

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I've checked all that several times. The only connection is screws on the back of the PID, and now the disconnect I added.

flananuts said:

How are you recirculating in your MLT? You could be experiencing channeling issues in your grain bed. Pics would be helpful. I use a HERMS method and found a way to put my RTD in a thermowell into the return line and find it very consistent.

pics always help

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I don't think it's a channeling issue. It's literally instantaneous jump of up to 20 degrees. Then a quick move of the wire puts it back where it should be. It's pretty obviously an inaccurate reading.

Pics may happen tonight. I'm at work at the moment.

i do agree its a wiring issue. its clearly not the actual temperature swinging 20+ degrees in under a second. an internal controller wiring fault is possible if the other connections are definately good, since it has happened on more than one thermocouple.

audger said:

i do agree its a wiring issue. its clearly not the actual temperature swinging 20+ degrees in under a second. an internal controller wiring fault is possible if the other connections are definately good, since it has happened on more than one thermocouple.

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I've been wondering about that. I hate to spring for a new PID if it's not the issue. I've already blown enough money on thermos. :cross:

Is it possible there's something else inside my project box causing interference?

TC wire is brittle as hell and doesn't tolerate a lot of repeated movement. Throw it out and get an RTD. You'll never look back, I promise.

jkarp said:

TC wire is brittle as hell and doesn't tolerate a lot of repeated movement. Throw it out and get an RTD. You'll never look back, I promise.

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[OP] Check first to make sure your PID model supports a RTD.

I agree, RTD is superior. I have thermocouples. I've experienced exactly what the OP is describing. Had to take apart the 2-prong thermocouple connector and rewire it.

jkarp said:

TC wire is brittle as hell and doesn't tolerate a lot of repeated movement. Throw it out and get an RTD. You'll never look back, I promise.

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Tempting. That's another $30....

I understand how a TC works, how does an RTD function? Is it less finicky about different metals in contacts?

curlyfat said:

Tempting. That's another $30....

I understand how a TC works, how does an RTD function? Is it less finicky about different metals in contacts?

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RTDs are resistors.

RTDs can also be extended using any thin wire, (18-22 gauge)...without impacting their performance.

If you want cheap and robust, get yourself one of these suckers:
http://www.ebay.com/itm/RTD-PT100-T...ultDomain_0&hash=item3a53cc96fc#ht_1673wt_905

(future thread readers, search ebay for "terminal RTD").

$16 and they are Walker Approved™. I just bought one yesterday, dude already marked it as shipped. Can't wait. (Oh, 4"ish probe, 1/2" NPT thread)

passedpawn said:

[OP] Check first to make sure your PID model supports a RTD.

I agree, RTD is superior. I have thermocouples. I've experienced exactly what the OP is describing. Had to take apart the 2-prong thermocouple connector and rewire it.

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Good to know others have experienced it.

shortyjacobs said:

RTDs can also be extended using any thin wire, (18-22 gauge)...without impacting their performance.

If you want cheap and robust, get yourself one of these suckers:
http://www.ebay.com/itm/RTD-PT100-Temperature-Sensors-Terminal-Head-/250514020092?pt=LH_DefaultDomain_0&hash=item3a53cc96fc#ht_1673wt_905

(future thread readers, search ebay for "terminal RTD").

$16 and they are Walker Approved™. I just bought one yesterday, dude already marked it as shipped. Can't wait. (Oh, 4"ish probe, 1/2" NPT thread)

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I might order this quickly.

curly... fyi you could have posted this in equipment and sanitation also... lots of systems are using temp sensors and PIDs

OneHoppyGuy said:

curly... fyi you could have posted this in equipment and sanitation also... lots of systems are using temp sensors and PIDs

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Thanks.

If you decide to go rtd I buy mine through some guys in Hong King that will make them custom. For example I had rtd sensors with metal springs at the sensor and cut with 1/4" not thread and custom wiring length. The actual rtd length was custom too. I don't think they were more than 20 bucks with shipping from HK. Pro-con was the name

I guess I have been lucky but I have never had trouble with thermocouples. I bought 25 ft of k type thermocouple wire on ebay. I cut it to desired length, hooked it up to my pid and twisted the other ends together. I built thermowells and stuck the twisted end into the thermowell. I have never had problems. I bend my wires all the time as I use one pid as a monitoring thermometer and move the thermocouple from the MLT output to my plate chiller output during every brew day.

Hilarious that I just gave pro-con products a shout out. They will custom make what you need and deliver quick.

flananuts said:

Hilarious that I just gave pro-con products a shout out. They will custom make what you need and deliver quick.

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Why is that hilarious? Did I miss something?

curlyfat said:

Why is that hilarious? Did I miss something?

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Because they are the company selling RTD's mentioned in the eBay link. :rockin: