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Old 10-16-2012, 01:59 AM   #1
TnFarmer
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Default Temperature probe location

I have a temperature controller for an extra fridge that we have. I mainly make ales and I have a couple of questions.
1. Should I secure the temp probe to the side of my primary carboy?

2. Should I set the temp controller to the low end or even slightly below the low end of the recommended temps for my yeast to account for the heat being given off?

Thanks

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Old 10-16-2012, 02:05 AM   #2
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Ideally you would use a thermowell which places the probe down the center of the liquid. With that you can set the temperature on the exact number you desire. Otherwise, tape the probe to the side of the carboy/bucket along the middle with some foam or bubble wrap over it. I would suggest setting the temperature on the bottom value of the recommended range in this scenario.

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Old 10-16-2012, 03:49 AM   #3
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Quote:
Originally Posted by jeepinjeepin View Post
Ideally you would use a thermowell which places the probe down the center of the liquid.
This may not be a good idea, as you can get some severe oscillation /overshoot in temperature. The body of liquid that is your beer will have a huge thermal mass, and as such a probe in a thermowell will react very slowly to temperature changes.

Example: you put a temperature probe in wort at 70 and want to chill to 65. This could take a couple hours. Until that temperature is reached, your cooling device, perhaps a freezer, will be active. This would cause the compartment to become far colder than you intend.

If you do something like a thermowell, you need a "smarter" PID controller.

My suggestion is to just set the temperature probe near the fermenter (lately I've been placing mine on top of the buckets I've been fermenting in.) This will get you some pretty stable temperatures.
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Old 10-16-2012, 04:02 AM   #4
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What stephelton says is true. I have five probes logging data. It has always been better to control the temp outside the fermentation vessel. You will get wild swings if you run the controller based on core temp or side of vessel.

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Old 10-16-2012, 04:09 AM   #5
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It might just be my set up but I have never experienced these "wild swings" with my thermowell. The most my system has ever overshot the set point was 0.5 C and that was only when the initial temperature was far off from the set point. It then rises to the end of the deadban (0.5 C) and turns back on. After its fairly close to the set point, the range is about -0.2 to +0.5 C. I'm just using a simple on/off relay with my fridge.

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Old 10-16-2012, 04:12 AM   #6
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Quote:
Originally Posted by stephelton

This may not be a good idea, as you can get some severe oscillation /overshoot in temperature. The body of liquid that is your beer will have a huge thermal mass, and as such a probe in a thermowell will react very slowly to temperature changes.

Example: you put a temperature probe in wort at 70 and want to chill to 65. This could take a couple hours. Until that temperature is reached, your cooling device, perhaps a freezer, will be active. This would cause the compartment to become far colder than you intend.

If you do something like a thermowell, you need a "smarter" PID controller.

My suggestion is to just set the temperature probe near the fermenter (lately I've been placing mine on top of the buckets I've been fermenting in.) This will get you some pretty stable temperatures.
The "huge thermal mass" would be slow to change temperature, but the probe being in the center of it would change quickly according to its surroundings.

When making a large temperature change the compartment will be warmer or cooler than the bucket. This doesn't matter though. We are concerned with the temp of the wort not the chamber. It may swing past the desired temperature a few times due to the outside of the bucket being heated or cooled quicker than the wort can conduct the heat all the way through. My suggestion there would be to chill the wort to below yeast pitching temperature and let it warm without a heat source to pitch temp and then pitch the yeast. That should eliminate any temperature swings of any consequence.

He said he has a temperature controller.
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Old 10-16-2012, 04:16 AM   #7
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Quote:
Originally Posted by pelipen
What stephelton says is true. I have five probes logging data. It has always been better to control the temp outside the fermentation vessel. You will get wild swings if you run the controller based on core temp or side of vessel.
Now this interests me. What is your setup like. Are the five probes on separate vessels? Separate chambers? Airflow?
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Old 10-16-2012, 04:18 AM   #8
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Sorry, I totally thread-crapped on you. I'll take a stab at your other question:

Quote:
Originally Posted by TnFarmer View Post
2. Should I set the temp controller to the low end or even slightly below the low end of the recommended temps for my yeast to account for the heat being given off?
I usually try to set the setpoint and range/tolerance around the average temperature I want. I've got a Marzen fermenting right now which I wanted to ferment about 51. So I set the setpoint (the point at which the controller deactivates) to 50 and the range (the amount the controller will tolerate before activating) to 2. This means the controller swings from 50 to (50 + 2) which should average close enough to 51.
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Old 10-16-2012, 04:19 AM   #9
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Quote:
Originally Posted by stephelton
If you do something like a thermowell, you need a "smarter" PID controller.
How would a PID work with a fridge? A PID controller looks at the magnitude of the error, the integral of the error, and/or how fast the error is changing. It then adjusts the output according to the tuning parameters. Fridges are simply on or off so you can't adjust the output.
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Old 10-16-2012, 04:31 AM   #10
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Quote:
Originally Posted by Ryush806 View Post
How would a PID work with a fridge? A PID controller looks at the magnitude of the error, the integral of the error, and/or how fast the error is changing. It then adjusts the output according to the tuning parameters. Fridges are simply on or off so you can't adjust the output.
PID:

P - proportional - represents the absolute difference between setpoint and actual temp at a given time
I - integral - accumulates as error is not corrected
D - derivative - represents the change in "direction" (are we getting better or worse)

Your output is either on and off, as you say. At any instantaneous point in time, you could be either on or off, but over a period of time, you could potentially be on and off in any combination (on for 5 minutes, off for 5 minutes). A PID controller that I wrote for a fermentation chamber I built a few years ago does just this. The trouble with a compressor (e.g. a freezer / fridge) is that it's duty cycle has a large impact on its lifespan.

However, in my original example, a PID controller could certainly be used to avoid excessive overshoot. The contribution of D (the derivative) is what would allow a PID controller to work in this case.
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