Spike Brewing 12.5 Conical Fermenter Giveaway - Enter Now!

Home Brew Forums > Home Brewing Beer > Electric Brewing > Multiple RTD's?

Reply
 
LinkBack Thread Tools
Old 01-02-2013, 01:15 PM   #1
goybar
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2010
Location: Southern Maine
Posts: 250
Liked 6 Times on 6 Posts
Likes Given: 2

Default Multiple RTD's?

Can you use multiple RTDs sensors on a PID?

Multiple inputs to help get more consistent temperature throughout the mash?

I do BIAB, and recirculate with a pump, I monitor the temperature from the bottom of the kettle (sight glass with Thermometer), and at the wort return (into mash).

I'm currently using propane, but will be going electric once the funds and plan is finalized.

I would like to insert a thermowell into the lid of the BK/MT to get a reading there as well as under the "false bottom" (wire rack today/possibly Bayou Classic basket in future).

Am I just being to overly concerned about consistent mash temps?

As long as I'm recirculating it really shouldn't be an issue?

Should I just RDWHAHB?

Chris

__________________
goybar is offline
 
Reply With Quote Quick reply to this message
Old 01-02-2013, 02:37 PM   #2
aquenne
Feedback Score: 0 reviews
Recipes 
 
Join Date: Oct 2011
Location: Paris, Ontario
Posts: 226
Liked 5 Times on 5 Posts
Likes Given: 6

Default

A PID controller will perform best when controlling 1 enviroment. When you run the auto tune to set the P, I and D gains, the controller is measuring the way the system reacts to changes (the "inertia"). The various places were you want to have different sensors would change those auto tune terms.

For the price of a PID controller, I would run seperate ones for each control location.

__________________
aquenne is offline
 
Reply With Quote Quick reply to this message
Old 01-02-2013, 09:13 PM   #3
warthog
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2006
Location: Park City, Utah
Posts: 63
Liked 1 Times on 1 Posts
Likes Given: 2

Default

most pid controllers have only one rtd input. if you were to attach multiple sensors, the result would likely be totally messed up. rtd's are resistance based, a bunch of resistors in parallel will not give you the average resistance. 1/r= 1/r1+1/r2, so your resistance is exactly 1/2 the average resistance (since you are thinking about using 2 probes - it would be 1/3 the average with 3 probes, and so on). the resulting temperature will be considerably lower than the actual temperature.

choosing the best location for a probe, is always a challenge (unless you are an alien abductor). in reality, you will have hot spots and cold spots, even if you recirculating. but they will be very small variations. i assume that you are actually recirculating the runnings, (as opposed to running a loop of hot water around your bag) in which case i would suggest that you monitor the temperature of the recirculating wort, as it reenters your BK/MT. you will likely have to apply some offset, to equate the temperature of your returning wort to the average temperature of your mash. we all play around a bit to figure out what the best settings are for our particular brewing rigs.

__________________

more beer for me

warthog is offline
 
Reply With Quote Quick reply to this message
Old 01-03-2013, 11:58 AM   #4
aquenne
Feedback Score: 0 reviews
Recipes 
 
Join Date: Oct 2011
Location: Paris, Ontario
Posts: 226
Liked 5 Times on 5 Posts
Likes Given: 6

Default

oh I took what you wanted to do was switch inputs from various sensors.

If your thinking about hooking up multiple RTDs, you will need to create some kind of conditioning circuit to average the resistances. Its do-able, but your probably further ahead, to stick with one sensor.

__________________
aquenne is offline
 
Reply With Quote Quick reply to this message
Old 01-03-2013, 12:29 PM   #5
goybar
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2010
Location: Southern Maine
Posts: 250
Liked 6 Times on 6 Posts
Likes Given: 2

Default

Thanks for the replies.

Warthog, yes I recirculate by taking the wort from the bottom (ball valve) and pumping it back up through the lid. I currently play the game of monitoring both the output and input of the wort and trying to adjust the temperature manually. Going electric and using a PID will in all likely hood be better and more consistent than my curent method.

Aquenne, I was thinking/hoping that the PID might be able to read multiple rtd's at the same time and use its logic and auto tuning to compensate for the differences.

It was just a thought. I'll stick with one RTD...... and try to figure out the best placement...

Chris

__________________
goybar is offline
 
Reply With Quote Quick reply to this message
Old 01-03-2013, 03:25 PM   #6
BadNewsBrewery
Basement Brewer
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
BadNewsBrewery's Avatar
Recipes 
 
Join Date: Oct 2012
Location: Severn, MD
Posts: 1,083
Liked 108 Times on 89 Posts
Likes Given: 38

Default

I have my RTD in a tee off the outlet from the tank, before it goes into the pump. It's the same way Kal does it, and in my opinion the best way - you get a steady flow of liquid (no stagnation) and with the pump running your constantly getting a nice mix too.

__________________
Building a Bad News Brewery - eHERMS

2014:
5gal Scottish Wee Heavy
5gal Saison
15gal American Pale Ale
20gal Belgian Wit (10 dumped)


Keg 1: Apfelwein
Keg 2: Belgian Wit (Failure)
Keg 3: American Pale Ale
Fermenting: Belgian Wit (Take 2)
BadNewsBrewery is online now
 
Reply With Quote Quick reply to this message
Old 01-03-2013, 07:10 PM   #7
jCOSbrew
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2012
Location: Colorado Springs, CO
Posts: 611
Liked 37 Times on 33 Posts
Likes Given: 7

Default

I use a cheap waterproof rtd and stick it right in the middle of the mash. In theory the input or output temp should be just as accurate with good recirc and the correct offset.

If you want to check extra temps an oven or BBQ thermo might work. I have also seen some panel mount thermometers for about $5 on eBay and amazon.

__________________
jCOSbrew is offline
 
Reply With Quote Quick reply to this message
Old 01-03-2013, 08:25 PM   #8
Shockerengr
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2007
Posts: 438
Liked 20 Times on 17 Posts
Likes Given: 1

Default

it's possible to wire 4 RTDs together in a way that averages their readings together. it would appear to the PID as if it was a single RTD, but you'd be getting an average reading.

That would only work if they are all reading the same enviroment however (say 4 different spots of the mash tun)

To wire it, you put two sets of RTDs in series, and then run those two sets in parallel.

This may not be what you're after however.

__________________
Shockerengr is offline
 
Reply With Quote Quick reply to this message
Old 01-03-2013, 08:36 PM   #9
warthog
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2006
Location: Park City, Utah
Posts: 63
Liked 1 Times on 1 Posts
Likes Given: 2

Default

not a bad idea. it should work

__________________

more beer for me

warthog is offline
 
Reply With Quote Quick reply to this message
Old 01-03-2013, 10:41 PM   #10
goybar
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2010
Location: Southern Maine
Posts: 250
Liked 6 Times on 6 Posts
Likes Given: 2

Default

Quote:
Originally Posted by Shockerengr View Post
it's possible to wire 4 RTDs together in a way that averages their readings together. it would appear to the PID as if it was a single RTD, but you'd be getting an average reading.

That would only work if they are all reading the same enviroment however (say 4 different spots of the mash tun)

To wire it, you put two sets of RTDs in series, and then run those two sets in parallel.

This may not be what you're after however.
That is inline with what I had in mind.

So if it is possible, does it make sense to do it?

Will the results lead to a more efficient, consistent mash, that is repeatable?

Or will it led to a less consistent mash, or end up with a mash that is too high or low than intended?

Is it worth the expense of an additional 3 RTDs?

Anything will be more consistent than my current method, which will no doubt lead to better results.

But I would also like to make the system, with in reason, the best it can be.

Chris
__________________
goybar 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
Multiple Burners Multiple Tanks oakbarn Equipment/Sanitation 1 08-28-2012 03:03 PM
Many RTD's only one controller yellow Electric Brewing 14 03-28-2012 07:54 AM
For Sale - Auber PID's, timer, RTD's fastev For Sale 6 02-08-2012 05:49 PM
Best locations for RTD's cdelap DIY Projects 8 02-07-2012 08:25 PM
Multiple mashes? bjl110 Beginners Beer Brewing Forum 2 01-01-2012 05:22 PM



Newest Threads