Howto: Calibrate Temperature Probes

Describe your system and processes, and post your config file.
mellman
Posts: 23
Joined: Thu Mar 20, 2014 7:19 pm
Bot?: No

Re: Howto: Calibrate Temperature Probes

Post by mellman » Sun Oct 23, 2016 3:31 pm

The bcs is grounded to earth ground, probe ground is connected to ground on the bcs.

Tempos don't swing, they move a few tenths in the water bath but they seem as stable as my thermogenesis except they're off by a few degrees

User avatar
bbrally
Posts: 196
Joined: Sat Mar 27, 2010 3:59 am
Bot?: No
Location: Vancouver, BC or NST, Thailand
Contact:

Re: Howto: Calibrate Temperature Probes

Post by bbrally » Sun Oct 23, 2016 5:01 pm

A couple things that may affect the results:

When you place the probes in the water, don't let them rest against the sides or bottom of the vessel, they will read a different temp than the water. I hold all my probes by the cables and place as much of them in the water as I can while gently moving them in the water. This will also keep the water temp the same throughout the bath. You can watch the temps or resistances from another temp/restistance logger window to see when they stabilize and then lock them in.

You might also try spreading your sampling temperatures out. I'm just guessing, but perhaps having a narrower range may require you to be more accurate with temps and resistances than the equipment will allow.

I calibrated mine at 32, 150, and 212, using three water baths next to the stove. The first and last are easy and don't even require a seperate thermometer. For the ice bath, let the ice/water sit for a bit in the fridge. It takes a bit of time for the ice to bring the water close to 0. Stir the ice/bath with the probes while reading. Ideally the water will be at zero, but the ice could be several degrees colder. Stir the bath so the ice doesn't rest against a probe.

In the past I played around with the numbers while calibrating probes and noticed that a temperature entered off by just one degree could pull the coefficients negative.

I've calibrated dozens of probes with this method and haven't had any problems.

I don't think it has anything to do with your cabling, your resistance values don't look completely off. And any small deviance would be compensated for by the calculator.
Move, copy, clear processes/states: http://manipulator.from-ca.com/
Perform coefficient mods: http://calculator.from-ca.com/
HMI Builder: http://bbrally.altervista.org/GUI/index.html
HMI Builder latest ver: http://bbrally.altervista.org/guibeta/index.html

User avatar
oakbarn
Posts: 761
Joined: Thu Jan 05, 2012 2:28 pm
Bot?: No
Location: Texas
Contact:

Re: Howto: Calibrate Temperature Probes

Post by oakbarn » Sun Oct 23, 2016 5:20 pm

Well worth the time to view:
Ice Baths are harder than you think.

http://www.thermoworks.com/learning/the ... an_icebath

User avatar
bbrally
Posts: 196
Joined: Sat Mar 27, 2010 3:59 am
Bot?: No
Location: Vancouver, BC or NST, Thailand
Contact:

Re: Howto: Calibrate Temperature Probes

Post by bbrally » Sun Oct 23, 2016 5:59 pm

Interesting read, learned a few new things.

I've wondered if the same is true of boiling water. A rolling boil would have more steam than a gentle boil. That steam could be hotter than 212, thus affecting its temperature reading.
Move, copy, clear processes/states: http://manipulator.from-ca.com/
Perform coefficient mods: http://calculator.from-ca.com/
HMI Builder: http://bbrally.altervista.org/GUI/index.html
HMI Builder latest ver: http://bbrally.altervista.org/guibeta/index.html

User avatar
oakbarn
Posts: 761
Joined: Thu Jan 05, 2012 2:28 pm
Bot?: No
Location: Texas
Contact:

Re: Howto: Calibrate Temperature Probes

Post by oakbarn » Sun Oct 23, 2016 6:56 pm

Boiling Water Bath:
http://blog2.thermoworks.com/2014/11/th ... libration/


But what is the Temperature of Boiling Distilled Water. You must use Pressure to be correct.


Denton Tx is the nearest airport to me (about 5 miles).

I use this Online Calculator that has either pressure or altitude for Boiling Point:
http://www.csgnetwork.com/h2oboilcalc.html

The elevation of the airport is 642 feet. It does not change. My exact height is 669 feet. If I use my elevation, I get a 210.866. I could use 210.9 but it is WRONG!

I use the barometric pressure of 30.11 and I get 212.318 so I would use 212.3. The ONLY way to figure the boiling point is pressure and not altitude which is a WAG!

You can use your own barometer and/or check the surrounding airports for pressure. On a non stormy day, pressure is generally the same in a local area of the same close elevation. If you wanted to get fancy look at an isobar chart for the area. Unless you are near a front or storm, your pressure will be the same as the nearest airport. This is generally true for days with a light or no wind.

mellman
Posts: 23
Joined: Thu Mar 20, 2014 7:19 pm
Bot?: No

Re: Howto: Calibrate Temperature Probes

Post by mellman » Sun Oct 23, 2016 8:06 pm

Thanks guys, I didn't realize being a tenth of a degree off would screw with things, ill try again tomorrow with the tips you suggested.

mellman
Posts: 23
Joined: Thu Mar 20, 2014 7:19 pm
Bot?: No

Re: Howto: Calibrate Temperature Probes

Post by mellman » Mon Oct 24, 2016 7:30 pm

In my best professor farnsworth voice - Good news everyone!

My 4 probes are calibrated. I did temps at 32, 152, and 202 (water only seemed to be boiling by my element). I tried at 180, and it definitely didn't like the variation. Now all 4 probes seem to sense within ~0.5 degrees of one another and I'm OK with that. Now that I have them calibrated, is there a way to backup the coefficients that are set so I don't have to do it again?

The "how to make an ice bath" piece really helped, i was definitely using too much water. Also having the temps spread out seemed to help as well, perhaps I lose a little accuracy but since one of my calibration points was at 152, and the mash temp is the one i care most about, i presume I'll be OK. Hopefully it'll be accurate between 110-160, or at least consistent.

Thanks to all for the help, to those of you trying to calibrate your probes...it took me 4 tries trying to do it the quick and dirty way. microwaving water didn't work, i just had to bite the bullet and boil 10g of water in my kettle (my probes/controller aren't exactly portable, and i figured it would be more work to replicate the cable lengths moving it all in to the kitchen.)

My wife helped out by keeping an eye on the probes and giving an extra set of eyes/hands, so that was a plus too!

Cheers all!
-Matt

User avatar
oakbarn
Posts: 761
Joined: Thu Jan 05, 2012 2:28 pm
Bot?: No
Location: Texas
Contact:

Re: Howto: Calibrate Temperature Probes

Post by oakbarn » Tue Oct 25, 2016 6:50 am

mellman wrote:In my best professor farnsworth voice - Good news everyone!

...t. Now that I have them calibrated, is there a way to backup the coefficients that are set so I don't have to do it again?

....

-Matt
A Normal Backup saves your Settings.

mellman
Posts: 23
Joined: Thu Mar 20, 2014 7:19 pm
Bot?: No

Re: Howto: Calibrate Temperature Probes

Post by mellman » Tue Oct 25, 2016 8:18 am

Can I migrate temp sensor 2 settings to temp sensor 5 though somehow? or even to another BCS?

User avatar
JonW
Site Admin
Posts: 1586
Joined: Sun Jul 18, 2010 7:51 am
Bot?: No
Location: Huntington Beach, CA
Contact:

Re: Howto: Calibrate Temperature Probes

Post by JonW » Tue Oct 25, 2016 10:46 am

mellman wrote:Can I migrate temp sensor 2 settings to temp sensor 5 though somehow? or even to another BCS?
Take a screenshot of your coefficients and just type them in when you move a probe. You might want to mark the probes so you can keep track of which coefficients go to which probes.

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest