Author Topic: PIDs and Thermocouples  (Read 912 times)

Offline zztop

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PIDs and Thermocouples
« on: May 02, 2013, 07:55:40 AM »
So i recently bought an electric turkey roaster and as other people have stated on here the temperature control on them aren't exactly stellar.   So I have a few arduino's and also have some Solid state relay's incoming from ebay for a meat curing project.  I'd also like to make my temperature controller for cheese making but I have a few questions:

1 - Can anyone recommend a specific thermocouple?  Prices range from $5 to easily $50.  I'd like something fairly reliable middle of the range price wise.

2 - A lot of recipes seem to call raising the milk X amount of degrees over X amount of time.  This is the reason why I'm going for the arduino instead of a standard pid because I figure I can code this functionality.  However I'm not against using a PID since it would be a lot less work for me but I want to know how people manage the temperature increases with a pid now?   Do you sit there and increase the temp on the PID manually for 45 minutes?

Any insight would be greatly appreciated.

Regards,
Michael



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Offline mdmoore00

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Re: PIDs and Thermocouples
« Reply #1 on: May 02, 2013, 09:51:17 AM »
I have had great success using an arduino as a PID. I used a Dallas DS18B20 one wire temp sensor http://www.adafruit.com/products/381.
The sketch was based on a toaster oven PID controller from this blog http://www.sleepyrobot.com/?p=292. I had to modify it but that's what great about open source.
It has a serial output that is graph able and will help adjusting the PID parameters.

I have since moved to a cheap Chinese PID poor quality functional. this uses a type k thermocouple. attached is the control unit I put together. Inside is a Solid State Relay that switches one of the receptacles  and the others are for the pump and other devices. I miss the ability to modify the arduino PID but i never really did that much after I dialed in the sketch. As far as adjusting the temp over time, it is quite easy. I just press the temp increase button 2 degrees every 5min or what ever is desired. Much more flexible during the make process.

Offline zztop

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Re: PIDs and Thermocouples
« Reply #2 on: May 02, 2013, 11:34:10 AM »
Great info mdmoore.

I looked at the adafruit thermocouple before but had concerns about the pvc jackets since the thermocouple will go into the curd and not the doubler boiler of the turkey roaster.

What are you using as your VAT?

Why did you end up switching to the PID and you have a link to where you bought the pid and thermocouple ?

Offline mdmoore00

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Re: PIDs and Thermocouples
« Reply #3 on: May 02, 2013, 12:29:40 PM »
The thermocouple is installed in a RIMS tube for my installation, beer brewing tech, http://www.mersonbrewing.com/rims.php. My vat in a water bath setup, i have three different sizes and I'm working on a converting a 120gal vat to a ~70 gallon jacketed vat (following picture). I switched to the PID because it is a engineered control and not a hobby controller. I think they both are equal. I would recommend an Auber Instruments PID controller and their thermo couples. I got an "Ebay Special" and it is crap but functional. 

Offline CheeWilly

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Re: PIDs and Thermocouples
« Reply #4 on: May 02, 2013, 10:38:59 PM »
I like the Auber controllers and thermocouples also.  Here are some choices that will get you started.
http://www.auberins.com/index.php?main_page=index&cPath=1
http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=109
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Offline kdttocs

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Re: PIDs and Thermocouples
« Reply #5 on: May 03, 2013, 12:24:07 PM »
I just thought I'd add that you may want to consider an RTD over a Thermocouple. Here's some info on the two:
http://ultra-nspi.com/information-central/rtd-termocouple-comparison/

Why it's a better choice for PIDs or PID-functioning Arduinos is the response times are slower and more stable with RTDs. This is important when you program/use PIDs as the quick and erratic temperature readings from a Thermocouple throw off the predictive functionality of the PID. The whole point of the PID is to achieve temperature stability while holding a temp and also changing temp. The PID not only monitors the temp but also how fast the temp changes. With erratic temp reads, it makes the fuzzy-logic really fuzzy.

With that said I have a PID using a Thermocouple :). What I ended up doing is insert the probe into a piece of silicone tubing slightly longer than prob. This serves both to buffer the probe from the swirling and erratic water bath temps and to also to ensure the prob tip remains off the bottom of the vat.


Note this is an old photo from when I was first testing my setup... all electronic are now nicely packed into the black box.

Offline zztop

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Re: PIDs and Thermocouples
« Reply #6 on: May 03, 2013, 02:59:22 PM »
I think I've decided to go with the following RTD with the deluxe cable:

http://www.auberins.com/index.php?main_page=product_info&products_id=270:81e9b9e13fa71611e311d9066e884534

and the following PID:

http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=3


I am considering the Ramp/soak option.  I know Wayne mentioned it in the following thread:

http://cheeseforum.org/forum/index.php/topic,10135.0.html


@kdttocs - I had read in another post the you have a pump in your roaster?  Is that submersed in the milk?  Is temperature host spots in the roaster ?


Regards,

Offline kdttocs

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Re: PIDs and Thermocouples
« Reply #7 on: May 03, 2013, 03:21:14 PM »
I built two types of vats. Both are water bath vats that I use a 2.5gal stainless steam table tray that sits in the water bath.

One was a RIMS setup like linked in previous post. That one I have a tub where the water bath is circulated from one side, into the RIMS-style heater controlled by the PID and out back into the tub at the target temp. While this was extrememly effective, it was over complicated and difficult to setup and tear down.

I then built what's in my photo which is a cheap turkey roaster that is controlled by the PID. I have a cheap $5 HarborFreight water pump that I drop on the water bath to circulate the water to even the temp. The roaster hold 4 gallons which I've seen someone to a 4 gallon batch directly in the vat but as I said, I do water batch style.

I should note that the turkey roaster setup also doubles as a great sous-vide machine. :)