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Old 01-18-2013, 12:31 PM   #21
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No problem. Is there a simple way to set the PID not to heat other than backing the setpoint down? Manual mode at 0%? Any other method?
The only ways I know are as you described. You could also unplug the RTD from the panel, which would cause the PID to go into alarm and stop sending signals. Unfortunately, the 2352 sounds an alarm tone if that happens (the SWA-2451 does not), so if you don't have an on/off switch on your alarm then that rapidly becomes a terrible idea.
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Old 01-18-2013, 04:21 PM   #22
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BadNews,

I have a single PID control panel that I just finished with one RTD going to my HLT and one to my BK, I plan on unplugging the RTD to the HLT and plugging in the RTD to the BK after I finish mash-in. I've tested this with a simple walk-through with water in my vessels but ran out of wire and never connected my alarm (my next to-do item) -I don't have a switch to turn off my alarm -is there any configuration setting that I can use in the 2352 to disable the alarm upon disconnecting an RTD? -I still want the alarm to go off when my BK reaches 205F, but I don't want it to go off when I swap RTDs.

Note: I do have an on/off switch for the PID controller itself. If I could just turn off the PID, then swap the RTDs and then turn it back on that is a workaround that would work for me, but I'd prefer to disable the "disconnected RTD" alarm.


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Old 01-18-2013, 04:23 PM   #23
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Apologize for the thread hijack; Badnews's post just instantly concerned me while I'm only 7 days away from brewing my first batch on this system.

Adam

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Old 01-18-2013, 05:58 PM   #24
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Answered via PM to stay on topic.

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Old 01-18-2013, 07:07 PM   #25
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I'm still baffled by the whole "fuzzy logic" terminology. It sounds to me like another way of describing the inherent function of PID. In other words, what makes PID smarter than a simple on/off controller that happens to have a hysteresis setting. When set point is a long way away, we expect the PID to run the element balls out until it gets close, then ease back on the power cycles as it gets closer and closer. . Autotune essentially tests a few different cycle times out to see how fast the system responds and then sets the PID values appropriately.

Auber seems to suggest this unit is different than typical PID function but I'm not smart enough to understand how.

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Old 01-18-2013, 08:32 PM   #26
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I'm still baffled by the whole "fuzzy logic" terminology. It sounds to me like another way of describing the inherent function of PID. In other words, what makes PID smarter than a simple on/off controller that happens to have a hysteresis setting. When set point is a long way away, we expect the PID to run the element balls out until it gets close, then ease back on the power cycles as it gets closer and closer. . Autotune essentially tests a few different cycle times out to see how fast the system responds and then sets the PID values appropriately.

Auber seems to suggest this unit is different than typical PID function but I'm not smart enough to understand how.
Bobby, I'm not smart enough either, but I did long ago understand fuzzy logic. It is really just a different method for expressing an algorithm, in an analog fashion in more or less natural language, rather than a digital one in equations. The advantage for a continuous control system should be that is easier for human beings to implement and optimize the algorithm, thus more likely (or less costly to get the algorithm there) to result in faster convergence to the setpoint and a tighter error band. I'm pretty sure that there is always an equivalent "traditional" algorithm to the fuzzy one, and vice versa.

While grossly oversimplified, the traditional algorithm would know that error = -10 def F, while the fuzzy one might have defined a function for "negative error" where anything greater than or equal to the setpoint would yield 0, anything less than 100 deg F below the setpoint would yield 1, and everything in between would yield something in between 0 and 1. Then the fuzzy algorithm could be specified with statements like "If error is negative then do x." It really just provides a layer of abstraction allowing for specification more "in words" than "in numbers."
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Old 01-18-2013, 09:00 PM   #27
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I really think we're over thinking this. Auber makes no mention of a "break in period" which is what this sounds like you're talking about. You autotune the device and so long as during the auto tuning you're running your pumps at the same flow rate as you would when you're pumping wort, the PID parameters will be set pretty darn close. The PID learns how much energy your system can put in and how much it losses. If you change that somehow then you need to re-tune.

Regardless, once set, it doesn't change those settings. I haven't seen my PID's overshoot their set temperature by more than 0.1*F.

I too am baffled a bit by the fuzzy logic statements. It tends to imply the values used are more of a possible range of values. Perhaps this is to offset some of the integral windup?

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Old 01-18-2013, 09:19 PM   #28
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I really think we're over thinking this. Auber makes no mention of a "break in period" which is what this sounds like you're talking about. You autotune the device and so long as during the auto tuning you're running your pumps at the same flow rate as you would when you're pumping wort, the PID parameters will be set pretty darn close. The PID learns how much energy your system can put in and how much it losses. If you change that somehow then you need to re-tune.

Regardless, once set, it doesn't change those settings. I haven't seen my PID's overshoot their set temperature by more than 0.1*F.

I too am baffled a bit by the fuzzy logic statements. It tends to imply the values used are more of a possible range of values. Perhaps this is to offset some of the integral windup?
Agreed regarding the over-thinking, but at least we answered the original question. Parameters change on autotune, or when you manually change them. End of story.

Now, back to the over-thinking on fuzzy logic. Yes, Auber's answer to me certainly implied that one thing the fuzzy logic algorithm does is detect an acceleration of the rate of change and offset the integral windup. Not that one could not do the same with a non-fuzzy algorithm, lol.
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Old 01-18-2013, 11:55 PM   #29
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And I thank ya for that!

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Old 01-21-2013, 03:32 PM   #30
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By reading that, I thought that if I just left my PID alone, it would learn the setup over time. I could force the learning by using Auto-Tune, but it wasn't a required step as the PID would work it all out. We now know that this is not true, per Auber.
Interesting. I did indeed think that the PID would (over maybe half a dozen or so batches) "learn" the system without having to manually force auto-tune. Based on this thread it appears this is incorrect and that you should force an auto-tune the first time the setup is used and every time you make any changes to the setup.

I'll go change it on my website just to be clear that auto-tune should be run. It'll be updated in a few minutes...

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No ding on Kal - like I said, he's the veritable Godfather of electric brewing. One bit of misinformation out of the veritable tomes he has written... that's not a bad average.
It still bugs me. I don't like mistakes.

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