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Process Control


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#1 cjc

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Posted 21 June 2011 - 06:15 PM

So I got a Netduino last Friday and so far I have been able to:
- Update it to the 4.1.1 1-Wire Beta firmware
- Get the serial-parallel LCD "Hello World" example going
- Read the temp of a DS18S20 1-wire temp sensor.

Fairly happy with stuff so far. (background: C# programmer by trade, home brewer by hobby, just learning more about netduino and circuits)

The plan is to get a Netduino Plus (Solarbotics is out currently, so just playing with a Netduino for now) to do the following:
- Read a 1-wire sensor network (automatic enumeration and simple config)
- Log data to the SD
- display process data on the LCD
- allow config files on the SD to be altered over Ethernet (e.g. push from a web server)
- allow data to be queried over Ethernet (e.g. pull to a web server)
- allow the process to be paused and started over Ethernet (e.g. push from a web server)
- Drive the process logic via config files on the SD
- Control relays based upon the process logic

Use Case:
Control gas and water valves and a pump for a HERMSsetup for step mashing, completely automated.

I know how I am going to accomplish most of this (but feel free to comment on anything), but I want a nice set of config files to define the process. I will be attempting to write something pretty generic (so it could be used for anything that needs to control relays based on sensors and time - like sous vide or fermentation temp control, or just weather logging). What I am hoping exists is a standard language for process definition so I don't need to invent my own (although I am good with that if need be).

E.G.
Step 1. Heat water to 77C
Step 2. Transfer 20L of water from HLT to MT
Step 3. Refill HTL.
Step 4. Heat water to 74C
Step 5. Recirculate water.
Step 6. Wait.
...

So for right now one question: Does anyone know of an industry standard "language" for process control config files? that's free? no too specific?

I figure I will need a file that abstracts things (the 1-wire sensor addresses into process controls, relays to actions, etc.) and a file detailing the actual process.

Once things gel a little more I will start posting the pieces of the project.

Cheers,
Corey

#2 Mario Vernari

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Posted 22 June 2011 - 03:32 AM

That's my main interest! Well, about the "programmability" it's a long debate. PLCs use primarily the ladder logic, but it is not enough, even for a simple task as yours. The most "powerful" PLCs embed a language similar to Pascal, that would be compiled into a standard machine language. All that is ISO-compliant, but it sounds much pretty like as the Netduino+MF already does. I dig a lot around this argument, and I considered that the best and simplest way is to program it using C#: simple, powerful and well-known. Also consider that alternative solutions would require resources that a Netduino Plus does not own. Hope it helps. Cheers
Biggest fault of Netduino? It runs by electricity.




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