Thermocouple Placement with PID

Started by robs, August 12, 2006, 08:58:35 PM

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robs

Quote from: bubbagump on August 14, 2006, 04:01:07 PM
Hi Robs,

What do you have your cycle time parameter set to and are you using an SSR output? If you are using an SSR output you should set your cycle time to either 1 or 0. The lower the number the faster the cycle rate and the less over or undershoot you will have. That's the beauty of using an SSR.

My PID is not the Auberin one but I did install one for another person. I had no luck at all running auto tune with Auber TC hooked up to it. I had temp swings and inaccurate readings. But then again you can't expect much of a TC for $5.00. As far as where to mount it goes I eventually mounted it to the inside of my garbage can.

After purchasing the Omega (I'm partial to Omega because I've had such good luck with them) I only had to run the auto tune once and it dialed right in. I didn't have to mess with any indivdual PID settings or program any offset in. The only parameter I changed was the cycle time. I think the default is 2 and I lowered it to 0.

There should be no reason that I can think of that auto tune would not work. When I run it I will place two bricks in the preheated smoker. Then I do not start autotune until the smoker is within 10 degrees of setpoint. If all parameters are set correctly and you have a good TC it should work fine.

I would compare the Auber TC against another digital thermometer to be sure it's accurate. You could also do the boiling water test instead.


Bubbagump


Yes, I am using an SSR.

Cycle time is set to 2. Maybe I'll drop it down and run AT again. Is measuring ice water accurate? My TC says 32, where my ET73 says 39 and 42.

I'm not giving up on the Auber TC just yet. Sure, the AT didn't work very good (could be the cycle or other variable), but once I tweaked some other settings, the sollution as a whole is working perfectly.

Thanks for the advice. I'll know after a few smokes if I need to get a new TC.

As for placement of the TC, I'm not sure that there is a perfect place. Above the food, it get's the food's vapor. Below the food and it get's the greese. The way you mounted it, is it touching any metal? Did you mount it on the back side, or side wall?

Thanks

rob

bubbagump

Rob,

That's another problem with the Auberin TC, since the probe end is so small it's difficult to mount it anywhere. I did not permanently mount my Omega TC. The probe end on the Omega I ordered is 3/16" x 3" long so I just took the mounting clip that came with my ET-73 and drilled it out to accept the Omega TC. I then run the TC down through the vent and clip it under one of the racks. Its postion varys depending on what and how much I'm cooking. I generally keep it to the outer sides so that it can sense the air temp. and not be affected as much by the temp. of the meat.

Bubbagump

robs

Quote from: bubbagump on August 14, 2006, 04:54:47 PM
Rob,

That's another problem with the Auberin TC, since the probe end is so small it's difficult to mount it anywhere. I did not permanently mount my Omega TC. The probe end on the Omega I ordered is 3/16" x 3" long so I just took the mounting clip that came with my ET-73 and drilled it out to accept the Omega TC. I then run the TC down through the vent and clip it under one of the racks. Its postion varys depending on what and how much I'm cooking. I generally keep it to the outer sides so that it can sense the air temp. and not be affected as much by the temp. of the meat.

Bubbagump

Bubbagump,

Do you think that grease, etc. from meats will damage the thermocouple? That's probably a stupid question.

Arcs_n_Sparks

Robs,

Thermocouples are one step above rocks and dirt on the technical food chain.... :D

TCs are two different wire types welded together. Unless you are putting them in an acid or alkaline bath, or using them over 1000 degrees, you would be hard pressed to do any damage to them.

Arcs_n_Sparks

bubbagump

Quote from: Arcs_n_Sparks on August 14, 2006, 06:48:10 PM
Robs,

Thermocouples are one step above rocks and dirt on the technical food chain.... :D

TCs are two different wire types welded together. Unless you are putting them in an acid or alkaline bath, or using them over 1000 degrees, you would be hard pressed to do any damage to them.

Arcs_n_Sparks

Ditto  :)