to PID or not to PID

I've been working on a temperature controller and researching control theories.  PID is proportional integral derivative control theory.  It's very quick to correct temperature but requires both a cold and heat source to work together.

My question is this.  Generally speaking, how quickly can a yeast be cooled without harm?

I've seen a recipe/process that recommended a temperature change of only 5F per day.  That seems pretty slow...

I 'think' the reason for going slowly is to prevent yeast shock/death, which might cause yeast to 'evacuate' undesirable compounds as they give up the ghost. 

Perhaps that is like hot-side aeration on our scale, and more a fear than a reality.  Dunno.

If you get it to pitching temperature, pitch yeast and the put it onto the controlled environment, I'm not sure where your problem lies.
You are only talking about a very few degrees of fluctuation and no matter how fast you change the temperature by two or three degrees it's not going to matter.
I am interested in what design you come up with though.
I'm planning on building something this winter.
I was thinking of something to do heat and cooling also.  I thought a freezer or large fridge wouldn't need much more than a light to heat it when it's indoors.  Cooling is obviously take care of.

My reason for concern was a recipe that required a full day to drop temp by 5 degrees F.  I have no experience in large temp changes so was hoping for some experienced input.

My gadget is entirely home grown using factory parts.  I use the CAINetworks "WebControl" which is a household (industrial) single board computer.  It has 8 temperature sensor ports along with 8 output ports.  There is a lot more "stuff" there but these 16 ports are what I use.

The board uses DS18B22 temperature sensors which are single wire sensors.  Actually they are V+ V- and a communications wire.

I put it into an acrylic Plexiglas box with a regular wall plug for my heat ( 60w light bulb ) and cold ( freezer ) AC plugs.  I put two mini-phone jack plugs in the face for my temp probes.  I actually have three but I split the one inside the freezer.  The probes are ROM coded so they can be paralleled with out mixing them up.  I also have a mini-phone jack for 12V to my computer fan inside my freezer.  The fan reduces over shoot of the freezer by a couple degrees.

The fun part is what I was asking in my post.  The webcontrol board has space for firmware code which actually makes decisions based on the temperatures read.

There are basically three theories on temp control.  PID is the hottest as far as intellectual investment.  I had it working but my freezer was working over time and I didn't want to wear it out early.  The next is SMC which is sliding mode control.  It is a better design theory for basic on off like a freezer but there is so little practical information.  The third is a basic home thermostat Bang Bang.  Really, Bang bang.  I'm not making that up. 

What I finally settled on was an intelligent bang and coast.  haha.  I take all three temperatures into a formula that predicts what temperature my freezer has to drop to in order to get my wort to coast to the target temp.

I can post a parts list if you're  interested.

Forgot to mention.  The temp probes I use are water proof so I put one into the wort for highly accurate temperature.

I did a log of my temp change from 75F to 62F and once it got there it maintained my temperature to plus or minus 0.2 degrees F.  Pretty sweet.

I'm curious what your using for relays on the output side of the controller. Reading the spec sheets on the controller the max output was 5 volt. Not sure if would be easier to use SC1000, where its 110volt and the hot and cold relays build into the controller.

I use SSRs ( Solid State Relay ).  I tried mechanical relays rated at 110vac and 10amps ( my freezer runs at 1.8a but surges to 8a on start up ) but the constant on/off eventually fused the contacts closed.  I woke up to find my fermentation bucket frozen solid and my freezer temp at 28F.  Fortunately it was a test run and the bucket was filled with water.

I bought them on ebay but they are also available at "Marlin P. Jones & Assoc. inc.", www.mpja.com.  On ebay they can be found for $3 to $5 or retail at about $8 for a 480vac 10a relay.  They trigger on 3 to 32 vdc and draw 6 to 20ma.  The output on the webcontrol board has 20ma available so at only 5vdc trigger from the board I figure the relay is drawing about 10ma max.

Be sure to buy only brand new unused relays.  I bought a couple used and one failed; this time on the heat side.  My 200 watt bulb melted some of the inside of my freezer. haha.  Some of the plastic liner on the lid looks like it has pimples. 

That's pretty neat. Did you ever consider the bcs-460? Seems like it has a lot of neat software interfaces.

Just did check out the bcs-460.  It looks way more complex than what I'm doing.  I only have a boil kettle and a freezer so I don't need anything that complex.  Maybe after I win the lottery.

My gadget was built for under $100 in parts.  It's a DIY gadget that happened to hit it right, so far.  I do have a little software that both makes the HTML user interface available but will log temperatures as well.  Over time I expect to create a more robust user interface but for now I'm just making beer and feeling my way around in side my freezer.

Thanks for the tip though.

BTW: here is a pic of my gadget, attachment.

MaltLicker:  Your reply seems most likely.  I know that yeast can't take large temperature changes but the size of "large" is a mystery.  I might just stick to 5F per day.  I'd hate to lose a batch just because I was impatient.

I may be gone for a while so I thought I should post some warnings about building your own temp controller using the cainetworks webcontrol board. 

First: look over the programming section of the user manual.  The PLC language used is not for everyone.

Then: take an inventory of the tools needed, like a drill press is very handy, and soldering iron is mandatory.

Then: check out your local Goodwill or Salvation Army stores.  My power supplies were all formerly wall warts or HP printer inline power supplies.  I get one with the voltage and current capabilities I need then crack open the case and wire it in.  $1.99 will buy what ever I need at my local stores.  I don't know where they get them but they are abundant.

Then: the next most difficult thing to obtain is a suitable enclosure.  I used acrylic plexi-glass because I had a sheet on hand and it was cheap (given to me).

Here is my code for the cool side of the controller.  I haven't coded the warm side yet but it will be almost identical.

‘ ************************ CODE ****************************
' ******************** RESET REGISTERS ***********
START
SET VAR1 600 ‘ SET POINT
SET VAR2 0 ‘
SET VAR3 80 ‘ Kp
SET VAR4 3 ‘ Ki
SET VAR5 0 ‘
SET VAR6 0 ‘ LOGIC FLAG
SET VAR7 0 ‘
SET VAR8 0 ‘ OUTPUT TEMPERATURE
 
SET RAM1 0 ‘ DECISION – HEAT OR COOL
SET RAM2 0 ‘ PROPORTIONAL
SET RAM3 0 ‘ INTEGRAL
SET RAM4 0 ‘ WORKING
SET RAM5 0 ‘
SET RAM6 0 ‘
SET RAM7 0 ‘
SET RAM8 0 ‘ WORKING

MAIN:
SUB T1 VAR1 RAM1 ‘ PUT DECISION INTO RAM1
TSTGT RAM1 0 ‘ TEST FOR AMBIENT HIGHER THAN SET POINT
CALLSUB COOL_DOWN ‘ TRUE JUMP TO COOL DOWN ROUTINE
DELAY 20000 ‘ WAIT A 20 SECONDS
TSTGT RAM1 0 ‘ TEST FOR AMBIENT LOWER THAN FREEZER
GOTO MAIN ‘ FALSE GOTO MAIN
CALLSUB WARM_UP ‘ TRUE JUMP TO WARM UP ROUTINE
DELAY 60000 ‘ WAIT A MINUTE
GOTO MAIN ‘ RETURN TO MAIN LOOP

END
‘ **** SUB ROUTINES ****
COOL_DOWN:
TSTLE T3 VAR1 ‘ Wort at setpoint?
GOTO COOL_OFF ‘ Yes? Then goto turn off below
‘ No? calculate target temp
DIV RAM1 VAR3 RAM4 ‘ DIVIDE BY Ki
SUB VAR1 RAM4 VAR8 ‘ SET OUTPUT TO SET TEMP – TARGET TEMP
SUB VAR8 VAR3 VAR8 ‘ SUB PROCESS VARIABLE
SUB T3 VAR1 RAM4 ‘ SUB WORT TEMP FROM SET POINT
SUB VAR8 RAM4 VAR8 ‘ SUB DIFFERENCE FROM OUTPUT
TSTGT T2 VAR8 OP2 ‘ Freezer Temp greater than output then turn on
‘ cool else turn off
RET ‘ Back to MAIN:
COOL_OFF:
SET OP2 0 ‘ Turn off the freezer
RET ‘ Back to MAIN:

WARM_UP:
SET VAR6 1 ‘ For test Logic only
RET ‘ Back to MAIN:


‘ ************************* END ****************************

I use MS Word for my editor.  PLC doesn't like comments so I put them all
the way to the right and use alt-left click and drag to select a vertical column
of text, with out the comments, to copy and past into the controller.

( Just my two cents worth) Boy that's a lot of code to turn a freezer and light on and off.

Large daily swings in temp are unusual, especially when dropping the temp.  I would guess that is a lager starting warm and dropping temp.  That has been pretty much debunked as process for homebrewers to speed up lagers. 

The temp controller is cool and gadgets are sweet but mostly overkill.  You can get perfectly accurate temps from the outside of the carboy so there is no need to risk contamination by inserting a probe.  I am much more worried about infection that .2F temp swing.  Actually, yeast work well with mild fluctuation in temperature.

I have used a simple analog temp controller on my fridge for years.  I tape the probe to the outside of my glass or plastic carboy with a piece of silver insulated bubblewrap from homedepot.  I have had to reduce the temp a number of times.  I simply adjust the dial down a two degrees and head to work in the morning.  After work, I dial it down a couple more.    By the next morning, I am at my target. 

In the winter, I have a heating pad against the carboy that comes on every 15 minutes on a simple dial timer.  The fridge keeps the temp of the wort pretty constant.  That is, whenever I open the door and look at it, the temp is right where I want it.

If a PID and electronic controller helps you make better beer, then I say go all in!  It is all about what works best for you.

Cheers!

I agree that .2F is not necessary.  I was looking for a degree F plus or minus but was surprised by the result I actually got.  The upside of the Webcontrol is that I can monitor my temperatures from my living room couch or from the Ukraine.

BTW: Overkill is fun too.

Thanks for the input.

+2

chasinreno said:

The upside of the Webcontrol is that I can monitor my temperatures from my living room couch or from the Ukraine.

Click to expand...