New Giveaway - Wort Monster Conical Fermenter!

Home Brew Forums > Home Brewing Beer > Automated Brewing Forum > DS18B20's or K-Type thermocouples




Reply
 
LinkBack Thread Tools Display Modes
Old 05-11-2012, 10:22 PM   #11
TheFlyingBeer
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2007
Location: Catonsville, MD
Posts: 425
Liked 13 Times on 12 Posts
Likes Given: 3

Default

I am using the DS18B20's throughout, made some tri-clamp thermowells for easy removal/cleaning:



The cost of monitoring additional temperatures throughout the brewing room becomes very low when using these digital sensors. Even at 750ms polling for the highest resolution you can use basic filtering to provide more timely inputs to control algorithms if needed.



__________________

Primaries: Air
Secondaries: Lakefront India Brown Ale

On Tap 1: Rootbeer, On Tap 2: NB White ouse Honey Ale, On Tap 3: Nitrogen, On Tap 4: Air, On Tap 5: Air
On Deck: DIPA, Imp Stout, Porter, Wheat, Black IPA

"No sense having empty carboys around when full ones take up just as much space. " - Me
TheFlyingBeer is offline
 
Reply With Quote Quick reply to this message
Old 05-12-2012, 01:14 AM   #12
kladue
Senior Member
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Dec 2006
Location: Turner, Oregon, Oregon most of the time now
Posts: 2,291
Liked 43 Times on 40 Posts

Default

Nice looking work there,
for your application the DS sensors would make sense as the process temperatures are not changing very fast with electric heating and the volumes involved. With the 10 bit resolution of the analog inputs on the Arduino platform the DS sensors make a lot of sense with the wide temperature range needed and lower resolution analog inputs available. It is when you get into higher heat inputs to small volumes that speed of response is needed, and increased resolution makes loop tuning easier with smaller steps in the input providing finer control of output.



__________________
kladue is offline
 
Reply With Quote Quick reply to this message
Old 05-12-2012, 01:49 AM   #13
TheFlyingBeer
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2007
Location: Catonsville, MD
Posts: 425
Liked 13 Times on 12 Posts
Likes Given: 3

Default

Quote:
Originally Posted by kladue View Post
It is when you get into higher heat inputs to small volumes that speed of response is needed, and increased resolution makes loop tuning easier with smaller steps in the input providing finer control of output.
Couldn't agree with you more. I would think that the thermowell or mechanical sensor interface is critical in high frequency measurements as any additional thermal mass acts as a low pass filter/delay.

As always, that is a lot of pretty equipment you are putting together. Seems as if you have enough extruded aluminum to build a roller coaster.
__________________

Primaries: Air
Secondaries: Lakefront India Brown Ale

On Tap 1: Rootbeer, On Tap 2: NB White ouse Honey Ale, On Tap 3: Nitrogen, On Tap 4: Air, On Tap 5: Air
On Deck: DIPA, Imp Stout, Porter, Wheat, Black IPA

"No sense having empty carboys around when full ones take up just as much space. " - Me
TheFlyingBeer is offline
 
Reply With Quote Quick reply to this message
Old 05-12-2012, 04:19 AM   #14
kladue
Senior Member
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Dec 2006
Location: Turner, Oregon, Oregon most of the time now
Posts: 2,291
Liked 43 Times on 40 Posts

Default

The automated system is 4 years old now, and was just a make work R&D exercise to work out the design for an automated gas burning indoor brewing system. Software applications were another make work exercise that combined recipe with process control features to see what could be included and made to work. First application was built in Java, which sucks at native memory management, second was a conversion to .Net which eliminated the problems when displaying process graphics that Java has.
Now the next make work exercise is to come up with a comparable touch screen modular control system with analog outputs for proportional control, and a flexible application with run time setup that eliminates the need for hard code changes.

__________________
kladue is offline
 
Reply With Quote Quick reply to this message
Old 05-18-2012, 08:32 PM   #15
crane
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2011
Location: San Diego, CA
Posts: 248
Liked 20 Times on 17 Posts
Likes Given: 1

Default

When considering a thermocouple's accuracy keep in mind that you also need to take into consideration the cold junction compensation temp sensors accuracy. TC's work by creating a voltage across a junction between 2 dissimilar metals. When the 2 thermocouple wires reach the electronics you get a second junction between the wires and the connector going into the PCB. To compensate for this second (cold) junction you need another temp sensor (thermistor, RTD, thermal diode, etc) located close to the second junction to get the temp out at the end of the probe. In practice this works by reading the CJC sensor and converting that into volts based off of a look up table. The you subtract that voltage off of the voltage measured by the TC. Finally you use another look up table to convert from volts to temperature. Also thermocouples produce an extremely small voltage that needs to be amplified before it can be read by any ADC. Any inaccuracies in you amplifier circuit (op-amp and resistor tolerances) will affect your overall accuracy. IMHO TC's are not nearly as accurate as RTD's or thermistors and are a lot more difficult to implement properly.

__________________
crane is offline
 
Reply With Quote Quick reply to this message
Old 05-19-2012, 02:39 AM   #16
kladue
Senior Member
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Dec 2006
Location: Turner, Oregon, Oregon most of the time now
Posts: 2,291
Liked 43 Times on 40 Posts

Default

Given that the PIC and Atmel chips only offer 10 bit analog inputs, direct connected RTD's or thermocouples are out of the question. With a suitable IC built for thermocouple or RTD use, they can render reasonably accurate readings via a voltage or digital output, and boards are available for this purpose. Thermisters are not a linear device and require formulas to correct the response across a typical brew system temperature range, but with appropriate resistance selection will yield an output suitable for the low resolution analog inputs on the popular microprocessors.

__________________
kladue is offline
 
Reply With Quote Quick reply to this message
Old 06-03-2012, 07:54 PM   #17
carlisle_bob
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2012
Location: Carlisle, PA
Posts: 1,205
Liked 27 Times on 26 Posts

Default

Quote:
Originally Posted by kladue View Post
Given that the PIC and Atmel chips only offer 10 bit analog inputs, direct connected RTD's or thermocouples are out of the question. With a suitable IC built for thermocouple or RTD use, they can render reasonably accurate readings via a voltage or digital output, and boards are available for this purpose. Thermisters are not a linear device and require formulas to correct the response across a typical brew system temperature range, but with appropriate resistance selection will yield an output suitable for the low resolution analog inputs on the popular microprocessors.
Hi

Thermistors are also quite cheap and they are easy to cable (unlike thermocouples). Getting a bunch of cheap thermistors to directly interchange - not so easy. If you can calibrate them individually, then that's not an issue.

Bob
__________________
carlisle_bob is offline
 
Reply With Quote Quick reply to this message
Old 06-03-2012, 11:48 PM   #18
kladue
Senior Member
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Dec 2006
Location: Turner, Oregon, Oregon most of the time now
Posts: 2,291
Liked 43 Times on 40 Posts

Default

Thermisters are sensitive to source voltage fluctuations, one of the reasons they see limited limited use, and are found where accuracy and stability are not required.

__________________
kladue is offline
 
Reply With Quote Quick reply to this message
Old 06-04-2012, 01:33 PM   #19
crane
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2011
Location: San Diego, CA
Posts: 248
Liked 20 Times on 17 Posts
Likes Given: 1

Default

When I use thermistors I measure the voltage across the thermistor and across the ref resistor to take voltage supply fluctuations into account. I have not found a need to individually calibrate each thermistor when I sample this way.

__________________
crane is offline
 
Reply With Quote Quick reply to this message
Old 06-04-2012, 10:44 PM   #20
carlisle_bob
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2012
Location: Carlisle, PA
Posts: 1,205
Liked 27 Times on 26 Posts

Default

Quote:
Originally Posted by kladue View Post
Thermisters are sensitive to source voltage fluctuations, one of the reasons they see limited limited use, and are found where accuracy and stability are not required.
Hi

As long as you do a ratiometric reading (same reference to the thermistor bridge as to the A/D) the voltage fluctuations drop out first order. Since the thermistor has a very high rate of change in resistance versus temperature, it's potentially a very high resolution sensor. They are indeed used in high accuracy applications when resolution is the key parameter.

One example is here:

http://us.flukecal.com/products/temperature-calibration/probessensors/5640-series-thermistor-standards-probes


Bob


__________________
carlisle_bob is offline
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools
Display Modes