Ss Brewing Technologies Giveaway!

Home Brew Forums > Home Brewing Beer > DIY Projects > temperature conundrum
Reply
 
LinkBack Thread Tools
Old 08-04-2009, 03:27 AM   #1
psyber
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2009
Location: USA
Posts: 49
Default temperature conundrum

Currently, I am prototyping my PID software for what will (hopefully) become part of my electric rig controls and found something odd.

I have three temperature reading devices and all three are registering a different temp:
A digital aquarium thermometer: 76.3
A digital cooking thermometer: 78.8,
and a thermoresister (DS18B20) using Dallas 1-wire and an Arduino board: 75.5.

Supposedly the thermoresister is accurate w/in +-.5 degrees.

I realize that it is silly to expect them all to be in agreement, but this does beg the question of which is correct. Also makes me reconsider using this as my temp probe. Then again, some basic testing suggests that the DS is hypersensitive (which should be a good thing).

Any thoughts?

__________________
psyber is offline
 
Reply With Quote Quick reply to this message
Old 08-04-2009, 12:35 PM   #2
bakins
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2008
Location: West Georgia
Posts: 731
Liked 4 Times on 4 Posts
Likes Given: 1

Default

You have to calibrate them all - even the thermoresister. Do you have a good quality "lab" thermometer to use as a baseline?

__________________
bakins is offline
 
Reply With Quote Quick reply to this message
Old 08-04-2009, 01:05 PM   #3
HairyDogBrewing
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2008
Location: Mechanicsburg, PA
Posts: 580
Liked 4 Times on 4 Posts

Default

Try them in ice water (should be 32F) and boiling water (212F at sea level, less at altitude).
Consumer thermometers are usually off by several degrees.
I use a Thermapen which is certified as traceable to the NIST standard.
Beware of the Traceable brand thermometers.
There are several thermometer threads, everyone has the same problem.

__________________
HairyDogBrewing is offline
 
Reply With Quote Quick reply to this message
Old 08-04-2009, 01:08 PM   #4
Sawdustguy
Feedback Score: 1 reviews
Recipes 
 
Join Date: Mar 2009
Location: Manorville, New York
Posts: 2,772
Liked 28 Times on 25 Posts

Default

Quote:
Originally Posted by psyber View Post
Currently, I am prototyping my PID software for what will (hopefully) become part of my electric rig controls and found something odd.

I have three temperature reading devices and all three are registering a different temp:
A digital aquarium thermometer: 76.3
A digital cooking thermometer: 78.8,
and a thermoresister (DS18B20) using Dallas 1-wire and an Arduino board: 75.5.

Supposedly the thermoresister is accurate w/in +-.5 degrees.

I realize that it is silly to expect them all to be in agreement, but this does beg the question of which is correct. Also makes me reconsider using this as my temp probe. Then again, some basic testing suggests that the DS is hypersensitive (which should be a good thing).

Any thoughts?
Make up an "Ice Bath" (crushed ice and a little water) in a large glass. The Ice Bath will be at exactly 32* F. Try each of the thermometers on the Ice Bath and you will be able to tell which one is the most accurate. I spent a summer in a calibration lab during college and this is how we checked thermometers and thermocouples.
__________________

Guy

Sawdustguy is offline
 
Reply With Quote Quick reply to this message
Old 08-04-2009, 01:25 PM   #5
psyber
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2009
Location: USA
Posts: 49
Default

Quote:
Originally Posted by HairyDogBrewing View Post
There are several thermometer threads, everyone has the same problem.
::facepalm::: Why didn't I think to look before posting.

The ice bath test is a good idea, as soon as I figure out how to waterproof the resister I will give it a shot.

Thanks a bunch.
__________________
psyber is offline
 
Reply With Quote Quick reply to this message
Old 08-04-2009, 02:05 PM   #6
freddyb
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2008
Posts: 214
Liked 7 Times on 7 Posts

Default

Quote:
Originally Posted by psyber View Post
The ice bath test is a good idea, as soon as I figure out how to waterproof the resister I will give it a shot.
Stick it in one of Derrin's probe ends Welcome to Brewer's Hardware

That's what I went with for the DS18B20. Couldn't be happier.
__________________
freddyb is offline
 
Reply With Quote Quick reply to this message
Old 08-04-2009, 04:53 PM   #7
evanmars
EAC Wannabe
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
 
evanmars's Avatar
Recipes 
 
Join Date: Dec 2006
Location: Springport, Michigan
Posts: 831
Liked 26 Times on 19 Posts
Likes Given: 4

Default

Quote:
Originally Posted by Sawdustguy View Post
Make up an "Ice Bath" (crushed ice and a little water) in a large glass. The Ice Bath will be at exactly 32* F. Try each of the thermometers on the Ice Bath and you will be able to tell which one is the most accurate. I spent a summer in a calibration lab during college and this is how we checked thermometers and thermocouples.
The devices won't necessarily have a perfectly linear response. The most accurate at 32*F may be more inaccurate at 212*F. Since the temps we are working with are closer to 212 than 0, I'd check them at boiling after finding out what temperature water boils at at your elevation.
__________________
Consistency is only a virtue if you're not a screwup

Primary - 0
Secondary - 0
Kegged - 0
evanmars is offline
 
Reply With Quote Quick reply to this message
Old 08-04-2009, 09:35 PM   #8
jpc
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2009
Location: Santa Clara, CA
Posts: 1,910
Liked 60 Times on 45 Posts

Default

Quote:
Originally Posted by freddyb View Post
Stick it in one of Derrin's probe ends
Yeah, but I'd feel obliged to buy him dinner first...
__________________
jpc is offline
 
Reply With Quote Quick reply to this message
Old 08-05-2009, 03:28 AM   #9
psyber
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2009
Location: USA
Posts: 49
Default

Quote:
Originally Posted by freddyb View Post
Stick it in one of Derrin's probe ends Welcome to Brewer's Hardware

That's what I went with for the DS18B20. Couldn't be happier.
Wow, he even has compression fittings that double as weldless thermowells! I know what I am ordering this weekend.
__________________
psyber is offline
 
Reply With Quote Quick reply to this message
Old 08-05-2009, 03:41 AM   #10
psyber
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2009
Location: USA
Posts: 49
Default

Quote:
Originally Posted by evanmars View Post
The devices won't necessarily have a perfectly linear response. The most accurate at 32*F may be more inaccurate at 212*F. Since the temps we are working with are closer to 212 than 0, I'd check them at boiling after finding out what temperature water boils at at your elevation.
Good point.

I could be way off here, but if I have a pot of water boiling how do I know it is at the minimum boiling temp? That is, if boiling is anything > 212 how can I tell if I am at 212 or 240? Then again, the same can be said for ice cubes in water.
__________________
psyber is offline
 
Reply With Quote Quick reply to this message
Reply



Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Conundrum SmugMug Beginners Beer Brewing Forum 10 05-13-2009 09:56 PM
Keg conversion conundrum donshizzles DIY Projects 4 02-27-2009 09:53 PM
Gelatin conundrum McCuckerson General Beer Discussion 10 12-01-2008 06:36 PM
SQL Gurus: A conundrum... olllllo General Chit Chat 15 04-04-2008 10:04 AM