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Old 07-18-2012, 04:34 PM   #11
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Quote:
Originally Posted by carlisle_bob View Post
Hi

If you tape the probe to a keg, and then swap around kegs, your controll point is going to change every time you do anything. Regardless of where the controll point is, you *will* need to calibrate things. That calibration will only be valid for a single control location. Why do it the hard way? There is 100+ years of engineering experiance out there on how to do this...

Bob
If you tape the probe to the freezer wall, you will need to adjust the controller temperature every time the ambient temp outside the keezer changes.

There is no re-calibration needed if switching between 1 keg and another, because it is a direct indicator. This is exactly why it is the preferred method, along with numerous other benefits. In this case, the 'control location' never changes, and is irrelevant anyway, because we are using a direct indicator regardless of where the beer is positioned.

Your approach isn't even using a secondary indicator for feedback, it is using the primary input (cold freon) as the indicator.

I don't know what control theory you are using, but I have never heard of one that favors staying as far removed as possible from the primary indicator (the beer). Even worse, one that uses the primary input (cold freon in this case) as a secondary indicator.

And I understand your position that the beer acts as an integrator, which makes it possible to control the temp more tightly using a secondary indicator. I also understand that would involve much more tuning and dependence on ambient conditions, something which you repeatedly/conveniently leave out, and neither of which the average person on these forums has either the desire to do, knowledge of, or control over. They want the simplest and most suitable solution.

Using your logic and theory, using a small bottle will give the same results as your approach, without having to worry about cooling coil location and without needing any temp offsets- just adjusting the differential for acceptable cycling freq.

RE:control loop reacting fast- We don't want the control loop acting fast for compressor based systems. This is exactly why everyone (else) recommends putting the probe on something massive, setting a small differential (~1F) and the desired temp (~38F), then calling it good; while you, confusingly, recommend setting an abnormally high differential (8F) with the probe on some object whose temp is far removed from the beer temp, then go about searching for what temp to set on the controller to get the beer temp you want.

Does that about sum it up?

Maybe you and Cat22 should battle it out over 'probe in air' (even for fermenting according to him) and 'probe on cooling coil'. The common element to both of your arguments is the insertion of another controller (yourself) into the loop- Cat22 with himself adjusting the control temp offest multiple times a day/week during ferment, and you fiddling about trying to determine the proper temp offset and differential because you are using the primary input as the indicator.
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Old 07-18-2012, 04:50 PM   #12
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Originally Posted by carlisle_bob View Post
Hi
There is 100+ years of engineering experiance out there on how to do this...

Bob
The engineering that has been going into appliances for 100+ years is to figure out how to save $.02 while still getting 'acceptable performance', and making it past the warranty period. When building a keezer or ferm chamber, using appliance engineering tactics is not a good course to follow. Flat out copying them is even worse.
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Old 07-18-2012, 06:05 PM   #13
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I submerse my probe in water. Get a 20-30 minute cycle every 4-6 hours. I have mine set at 3 celcius with a 3 degree differential. Works flawlessly

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Keg #2: Empty :(
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Ferment #1: Empty :(
Ferment #2: Empty :(
Ferment #3: Empty :(

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Old 07-18-2012, 06:22 PM   #14
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I submerse my probe in water. Get a 20-30 minute cycle every 4-6 hours. I have mine set at 3 celcius with a 3 degree differential. Works flawlessly
I think some guys have had their probes get water damage even though they are 'waterproof'. Some use gel, or a thermowell of some sort to avoid this.

You could probably tighten your temp diff without too much extra cycling. If your current probe vessel is smaller than your smallest bottle/keg, you might be able to reduce cycling and/or reduce temp swings by putting the probe on/in a larger vessel.

Interestingly, for fermenting, strapping/taping the probe to the outside of the vessel, then insulating over it, works better than a thermowell in the middle of the vessel. This allows some influence of the chamber air on the probe to control overshoot as well as reduce cycling freq and help minimize the effects of short term air temp spikes (lid openings, new warm keg). It also prevents radial temp stratification in the vessel at late ferm stages caused by using a thermowell.
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Old 07-19-2012, 11:35 PM   #15
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Quote:
Originally Posted by cwi View Post
If you tape the probe to the freezer wall, you will need to adjust the controller temperature every time the ambient temp outside the keezer changes.

There is no re-calibration needed if switching between 1 keg and another, because it is a direct indicator. This is exactly why it is the preferred method, along with numerous other benefits. In this case, the 'control location' never changes, and is irrelevant anyway, because we are using a direct indicator regardless of where the beer is positioned.

Your approach isn't even using a secondary indicator for feedback, it is using the primary input (cold freon) as the indicator.

I don't know what control theory you are using, but I have never heard of one that favors staying as far removed as possible from the primary indicator (the beer). Even worse, one that uses the primary input (cold freon in this case) as a secondary indicator.

And I understand your position that the beer acts as an integrator, which makes it possible to control the temp more tightly using a secondary indicator. I also understand that would involve much more tuning and dependence on ambient conditions, something which you repeatedly/conveniently leave out, and neither of which the average person on these forums has neither the desire, knowledge, or control over. They want the simplest and most suitable solution.

Using your logic and theory, using a small bottle will give the same results as your approach, without having to worry about cooling coil location and without needing any temp offsets- just adjusting the differential for acceptable cycling freq.

RE:control loop reacting fast- We don't want the control loop acting fast for compressor based systems. This is exactly why everyone (else) recommends putting the probe on something massive, setting a small differential (~1F) and the desired temp (~38F), then calling it good; while you, confusingly, recommend setting an abnormally high differential (8F) with the probe on some object whose temp is far removed from the beer temp, then go about searching for what temp to set on the controller to get the beer temp you want.

Does that about sum it up?

Maybe you and Cat22 should battle it out over 'probe in air' (even for fermenting according to him) and 'probe on cooling coil'. The common element to both of your arguments is the insertion of another controller (yourself) into the loop- Cat22 with himself adjusting the control temp offest multiple times a day/week during ferment, and you fiddling about trying to determine the proper temp offset and differential because you are using the primary input as the indicator.
Hi

There are a few things that are pretty obvious here:

1) You don't do this for a living, and you are not an engineer. Indeed I am an engineer and I do this for a living. What you know is from reading threads and guessing at stuff.

2) For what ever reason, you have a really big issue with accepting that there are multiple valid ways to do this, each with their plusses and minuses.

3) There is absolutely no way you will ever listen to anything but your own ideas. You have made that abundantly and violently clear.

Bob
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Old 07-20-2012, 12:25 AM   #16
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fwiw, I'm also an engineer, been one since 1973, practicing multiple disciplines, and I think taping a temperature probe to a freezer wall is pretty much the opposite of a sound way to keep beer at any specific temperature.

Whether carboy or keg, I strap the probes on my Ranco controllers directly to the middle covered with a chunk of 1" thick closed cell foam insulation, set the desired beer temperature, dial in a degree or two of differential, then let everything work...perfectly. If I want raise or lower the beer temp I can do it at will and the controller will hit it on the nose and keep it within the differential. No short cycling, ever...

Cheers!

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Old 07-20-2012, 09:03 PM   #17
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Quote:
Originally Posted by carlisle_bob View Post
Hi

There are a few things that are pretty obvious here:

1) You don't do this for a living, and you are not an engineer. Indeed I am an engineer and I do this for a living. What you know is from reading threads and guessing at stuff.

2) For what ever reason, you have a really big issue with accepting that there are multiple valid ways to do this, each with their plusses and minuses.

3) There is absolutely no way you will ever listen to anything but your own ideas. You have made that abundantly and violently clear.

Bob
Indeed it seems pretty obvious that you are not very good at seeing the obvious. You also seem to be describing yourself, since I have already admitted that with enough tuning, your way can produce tighter control, it just isn't feasible.
You also conveniently and repeatedly leave out about 99% of the work involved in your approach.

Algorithm for your "probe on wall" approach:
(with some old school GOTOs in there just for fun)
Code:
IF you don't already know where it is.
   Find where the last place is that the cold freon reaches on the inner 
   wall of the freezer.
   Tape the probe as far away from that spot and next closest freon 
   line as possible.
Set the controller temperature to some magical offset number 'a bit', 
scientifically speaking, colder (or maybe warmer, who knows) than you want 
your keg.(Warning this temp setpoint + offset may change over time for a variety 
of reasons due to this approach) 
Set the differential to a magical number that will control cycling freq. 
(Warning this differential may change over time for a variety of reasons 
due to this approach)
IF your controller doesn't have ASD.
   Go to the store and buy a new freezer because your compressor is fried 
   due to a hot start condition.
IF you don't have an extra temperature monitor.
   Buy a temperature monitor to see what your actual beer temp is as a result
   of the secondary temperature setting on the controller.
Monitor your beer temp repeatedly waiting for it to stabilize.
(Should only take a week or so.)
IF it isn't at the temp you want
   adjust the offset
   GOTO: previous step
If your cycling frequency isn't acceptable
   increase the differential
   GOTO: step 1
IF the ambient temp external to the chamber changes
   GOTO: step 1
Algorithm for the direct indicator 'probe on vessel' approach:
Improved with a hard coded relative offset GOTO- for her pleasure.
Code:
Tape/strap the probe to a keg of beer, or some facsimile, then insulate.
Set the temp of the controller to exactly the temp you want your beer.
Set the differential to exactly your temp tolerance level (down to ~.5F).
Wait one day.
Drink your perfect temperature beer.
IF your cycling freq is too high.
   Use a larger facsimile, add a fan, or more insulation over the probe,
   or give up some temp tolerance in favor of compressor life.
   GOTO 3 steps previous
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Old 07-20-2012, 09:06 PM   #18
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Quote:
Originally Posted by carlisle_bob View Post
Hi

Indeed I am an engineer and I do this for a living.
Bob
Please provide a list of projects you have worked on. I need to know for personal safety reasons.
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Old 07-20-2012, 09:10 PM   #19
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Quote:
Originally Posted by day_trippr View Post
Whether carboy or keg, I strap the probes on my Ranco controllers directly to the middle covered with a chunk of 1" thick closed cell foam insulation, set the desired beer temperature, dial in a degree or two of differential, then let everything work...perfectly.
This approach is mandatory for Ranco's, at least all the ones I have seen in use for homebrewing (the ones sold at LHBS), since they do NOT have any ASD.
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Old 07-20-2012, 09:20 PM   #20
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Sounds like some of our brew brothers need a beer. Try what sounds logical to you and see what works. What works well for me is a 20oz water bottle with the probe (wrapped in a plastic bag to prevent corrosion) submersed, stuck through a hole drilled in the cap. The bottle sits on the hump.

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