Low Cost, High Accuracy Temperature Sensing with a Thermistor - Home Brew Forums
Register Now For Free!

Home Brew Forums > Home Brewing Beer > Electric Brewing > Low Cost, High Accuracy Temperature Sensing with a Thermistor

Reply
 
Thread Tools
Old 04-29-2013, 09:04 PM   #1
alien
Recipes 
 
Apr 2012
Philadelphia, PA
Posts: 1,235
Liked 68 Times on 59 Posts



via Dangerous Prototypes:

http://mikestirling.co.uk/2013/04/lo...-a-thermistor/

 
Reply With Quote
Old 04-29-2013, 09:29 PM   #2
TomDaniels
Recipes 
 
Oct 2012
Posts: 24

Should be even easier on a better Arduino or Raspberry Pi. Plenty of horsepower there to do the calculations in floating point even. No need for the interpolation stuff.

 
Reply With Quote
Old 04-30-2013, 12:24 AM   #3
alien
Recipes 
 
Apr 2012
Philadelphia, PA
Posts: 1,235
Liked 68 Times on 59 Posts


Depends how much you believe this statement. Arduino is 8 bit.

"The formula that is usually used for this calculation is the Steinhart-Hart equation, which is not well suited for calculation on an 8-bit micro."

 
Reply With Quote
Old 04-30-2013, 03:22 AM   #4
jCOSbrew
Recipes 
 
Feb 2012
Colorado Springs, CO
Posts: 619
Liked 38 Times on 34 Posts


Don't see how sensor cost is an issue compared to SS brewery parts.

 
Reply With Quote
Old 04-30-2013, 04:30 AM   #5
TomDaniels
Recipes 
 
Oct 2012
Posts: 24

Yeah, the Arduino is 8 bit, but how often do you need to compute this? I geeked out and looked at the Steinhart-Hart Equation. Looks like computing (ln) is the worst of it and you only need to do that once in that equation.

It could be inconveniently slow, but even on the Uno, the docs I found on the Internet suggest around 30,000 float divides/sec. Multiplies are 3 times as fast. So, it might take a millisecond or two on an Arduino.

On other older microcontrollers, it'd be a lot slower though.

Thanks to OP for giving this PhD in CS something fun to research for the evening.

 
Reply With Quote
Old 04-30-2013, 03:42 PM   #6
alien
Recipes 
 
Apr 2012
Philadelphia, PA
Posts: 1,235
Liked 68 Times on 59 Posts


There is a forum member called crane who has done all these calculations and verified the accuracy of simple thermistors over a useful range using the coefficients published in the datasheet.

I agree that for brewing we don't need the calculations to be all that fast so the look up table is overkill. It's nice to know how it is done though.

Cost is not a huge issue but there may be applications where thermistors are more useful or convenient. For example if you want to measure temperature by sticking a probe to the outside of a pipe I would use a thermistor because you can get thin ones that lie flat.

e.g. http://www.rapidonline.com/electroni...mistors-61185/

 
Reply With Quote
Reply
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Automated volume sensing idea/help MrNatural Automated Brewing Forum 64 08-26-2015 01:34 PM
BCS Level Sensing OneHoppyGuy Automated Brewing Forum 9 06-22-2012 09:27 PM
Fermenting temperature accuracy boomtown25 Beginners Beer Brewing Forum 4 07-06-2011 08:11 PM
Hydrometer accuracy at high temps rack04 Equipment/Sanitation 11 04-04-2011 02:41 AM
Temperature strips accuracy PavlovsCat Beginners Beer Brewing Forum 5 02-25-2009 08:29 PM


Forum Jump