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Old 07-20-2012, 02:13 PM   #71
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Originally Posted by Eighty2Fifty1 View Post
Okay, I set up your code into the original and it works fine. I take it that later I could set up a way to change the setpoint and deadband variables with buttons or something, so I don't have to rewrite the code every time. Now I need figure out how to set up a multiple sensor network, and a way to log everything.
Hi

As you network them up, be sure to include some "what if the network is down" protection in the code. It's easy to put that off as a do it later task. Usually later turns into never or it's a major re-write when you do get around to it. Much better to include at lest some basic checks and protection right from the start.

Bob
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Old 07-20-2012, 03:10 PM   #72
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Originally Posted by carlisle_bob

Hi

As you network them up, be sure to include some "what if the network is down" protection in the code. It's easy to put that off as a do it later task. Usually later turns into never or it's a major re-write when you do get around to it. Much better to include at lest some basic checks and protection right from the start.

Bob
Like if something gets disconnected or a sensor fails? I think the code that I started with had something that would send an error message to the serial port if the sensor returned -127 deg C or something like that. I take it to mean that a failed sensor will return that value? So I'm guessing that the way the code sits now, I'd get the error message, but it would keep the heat on. Sounds like a potential fire hazard. Maybe I could hardwire a thermal fuse in there to cut power if a temp gets above a set value, say 80 deg F. Is that what you mean or is there something else?
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Old 07-20-2012, 08:10 PM   #73
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Is overswing a big problem for people? My fridge must have really low thermal mass, or something. I just stick a probe on the side with a bit of insulation and do a .5 degree deadband. An elaborate formula has just never been necessary for me.
Overshoot isn't a problem for most things like a keezer or a ferm chamber made from a fridge/freezer. Like you say, the 'thermal interia' (for lack of a better term), of the freon continuing to cool after shutoff is very small compared to the mass of a typical batch. In fact, when the probe is taped to the side of the vessel under some insulation, there is some predictive input from the air temp which causes an early shutoff prior to the vessel temp reaching the setpoint. Same goes for activation, but causes early turn on. That is why 'probe taped to the side of the vessel' has been crowned king.

Because these guys seem to be interested in sub 0.00001F temperature control, I had mentioned adding a lot of thermal mass pre-chillled to ferm temp. There is a chance that during the active phase the passive mass's temp could be lowered enough to cause overshoot when the ferm slows down. Not an issue for most people.

Same as you, the physical improvements available- mass, fans, probe placement, etc.- to me, seem much simpler and effective than trying to dial in some control equation.
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Old 07-20-2012, 08:16 PM   #74
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If you read a lot about the UberFridge, what he did was have temperature measurement of the liquid and the air. He then wrote some logic into the PLC that did predictive control. Essentially working out the thermal response of each batch. He's got all sorts of graphs showing the validation of his design. It was a really well laid out project and I'm grateful for him sharing it all.
I read his stuff about a year ago, but haven't checked what his latest incarnation looks like. He seemed single mindedly focused on trying to do everything with the control equation/logic. He also had to hand tune every batch- not exactly a generalized control system. Adding simple physical improvements like I mentioned earlier could improve his system even further. Also, like I mentioned previously, taping to the side of the vessel under some insulation mimics what his control system does- predictive input. The only difference is you can do it with a $25 ebay temp controller and some foam, and just need to change the insulating factor to vary the predictive input.
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Old 07-20-2012, 09:49 PM   #75
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Hi

Since most people are controlling something other than a fermenter, it's not a very good example of what they are trying to do.

It is actually quite easy to do reasonably tight control (0.1F) of a normal keg sitting in a keggerator. There is a very large body of theory that lets you set it up. It can be done without unduly cycling compressors *or* wearing them out by running too long on each cycle.

Bob
I used the fermenter example because it is the more general/difficult case, and also because fermenting was specifically mentioned in the post immediately preceeding my post, as well as being the subject of the last few pages..

If you are (again) talking about controlling by placing the probe on freezer's wall as a secondary indicator for the controller input, please include your complete process, not just stating that 'a large body of theory' says it is possible.

Most people do not want to go to the lengths required to tune that type of system, especially when the temp variation can be limited to 1F quite easily by just placing the probe on/in the keg, or a facsimile, and setting the temp on the controller. No complicated hunting for a temp offset, or the proper differential- just set them directly on the controller.

Here is a link to my psuedo-code of your 'probe on coil/wall' approach and the 'probe on vessel' method.
http://www.homebrewtalk.com/f35/keez...4/#post4266918

Please feel free to add detail or submit your own version of the 'probe on coil' process, since the only information you have provided is regarding the method is - place the probe about halfway to somewhere, talk about theories, add magic, then... perfect temp control.
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Old 07-20-2012, 10:00 PM   #76
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I believe it boils down to "over-engineering is fun!"
I am a big fan of overkill. There is a difference, though, between state of the art, and making the best out of what you have.

Multi-input loops using fixed speed compressors became old school once variable speed compressors using either DC or VFDs became economical enough. Last I checked, the uber fridge guy still had to model every different batch and hand tune his loop. External ambient changes introduced even more tuning.
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Old 07-20-2012, 10:44 PM   #77
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Like if something gets disconnected or a sensor fails? I think the code that I started with had something that would send an error message to the serial port if the sensor returned -127 deg C or something like that. I take it to mean that a failed sensor will return that value? So I'm guessing that the way the code sits now, I'd get the error message, but it would keep the heat on. Sounds like a potential fire hazard. Maybe I could hardwire a thermal fuse in there to cut power if a temp gets above a set value, say 80 deg F. Is that what you mean or is there something else?
Hi

Sensor failure is something that's also worth thinking about.

With a network, the issues are usually with data buffering. If it goes into the buffer, but doesn't go out... there's only so much ram. The same sort of thing thing applies on the input side, gizmo looks for command input, waits , repeats. No network = a lot of repeats and waits. There are only so many CPU cycles.

Bob
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Old 07-21-2012, 01:30 AM   #78
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Quote:
Originally Posted by carlisle_bob

Hi

Sensor failure is something that's also worth thinking about.

With a network, the issues are usually with data buffering. If it goes into the buffer, but doesn't go out... there's only so much ram. The same sort of thing thing applies on the input side, gizmo looks for command input, waits , repeats. No network = a lot of repeats and waits. There are only so many CPU cycles.

Bob
So I'd want something that would take a faulty sensor out of the equation? Like if it returns an obviously wrong value, it stops using that sensor to cycle the heater and cooler?
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Old 07-21-2012, 02:26 AM   #79
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So I'd want something that would take a faulty sensor out of the equation? Like if it returns an obviously wrong value, it stops using that sensor to cycle the heater and cooler?
What to do when a sensor goes out depends heavily on what the sensor was reading.

You mentioned previously using multiple sensors at various locations, averaging them, then using that value to determine the set point to keep your ferment vessel at the correct temp? Is that still your plan?

You also mentioned the desire to control multiple active batches within one chamber space. Is that still the goal?
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Old 07-21-2012, 02:51 AM   #80
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My current plans involve 5 sensors in the chamber to run the controls, plus a sensor in my ice chamber and one on the outside of the entire chamber for data logging. I don't have the parts I need for a thermowell, and I'll be filling my conical tomorrow, so that'll have to wait for a few weeks until the IPA is done dry hopping

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