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<== Date ==> <== Thread ==>

Subject: Re: CSS BOY and Raspberry Pi?
From: Ryan Pierce <rdpierce@pobox.com>
To: "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Date: Sun, 10 Jan 2016 22:37:26 -0600
First, thanks for the responses, both on and off list about this.

To provide a bit more background, I've written two blog posts about the project covering brewing theory, systems design, and what I'm trying to accomplish. They also include a number of photos of the system. I still need to write about the physical fabrication, electronics, and software.

http://www.mackenziegems.com/2015/12/25/cnc-beer-part-1-overview-and-theory/
http://www.mackenziegems.com/2015/12/28/cnc-beer-part-2-system-design/

The test I mentioned involved the hot liquor tank. (Part 1, first picture, top center keg.) This is filled with water, and it contains a copper coil that the beer wort passes through. (Part 2, third picture.) I was asked offlist if I could move the temperature probes or add more of them. What I'm trying to control is the temperature of the water near the coil, which accounts for the probe placement. I'm trying to regulate the temperature of the wort at the output of that coil, so the water temperature near the coil is most important to me.

I know the probes themselves have a good deal of lag. They are digital DS18B20 chips that take 750 ms to sample. But they are sealed inside thin stainless steel tubes. Grabbing the outside of the tube with my hand for, say, 10 seconds and letting go produces no immediate change. Then, after I release it, I can watch as the temperature starts to climb. I also imagine there's lag for convection to carry the hot water up past the coils. And the bottom of the kettle is still hot, so even after cutting off the flame, it still transfers heat to the water.

Matt Pearson suggested for larger setpoint changes using a larger deadband that after a period of time resorts to a smaller deadband. That sounds like it will work, and I know I can code it easily. I'm also interested in whether there are generic algorithms that can compensate for systems with lots of lag time. Eric Norum suggested a Smith Predictor. After researching it, I think I understand how that works, but it requires me having a mathematical model of what the system behavior should be, which I'd need more research to develop. I also received an offlist suggestion about a lead/lag block. If I'm not mistaken, that uses a Laplace transform, yes? If so, again, I'll need to do more math research.

I didn't hear anyone mention building CSS BOY on a Raspberry Pi. Has nobody tried this? With inexpensive touch screens for the Pi, it seems like one could make a small panel mount control console for under $150. I'm definitely planning on trying this myself, but it's on the backlog of things to do after getting the first batch of beer brewed.

Thanks,
Ryan

Replies:
Re: CSS BOY and Raspberry Pi? Jeong Han Lee

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