Electronics?

[kladue]

Here is a I2C bus relay board that can be connected to the I2C pins on the connector plug http://www.ereshop.com/index.php?main_page=product_info&cPath=143&products_id=605. For isolated binary input here is another board for that http://www.ereshop.com/index.php?main_page=product_info&cPath=143&products_id=602. For analog inputs here is a board http://store.gravitech.us/i2c128anco.html or if you want a friendlier board with analog output http://www.bipom.com/products/us/643.html. These can be wired to share I2C bus and addressed individualy with jumpers. This is enough off the shelf I/O to handle most systems, and additional boards are available for thermocouple inputs alsohttp://www.bipom.com/products/us/319237.html(not cheap as it requires analog input board also).

 

[kladue]

After a bit more research it looks like a person could put together a control system with off the shelf hardware for flow, temperature, pressure inputs, and relay or dc output to SSR's. With basic soldering and wiring skills you could assemble a control system from the various boards and sensors out there, the schematic for complete system will still need to be built by user. The hardware is low cost per item but the complexity of the system will drive final part count and cost. The coding for I/O is not that complex, and user interface, sensor range/calibration, and control sequence code will need to be developed. The question now is what scale of system do you want to build and how much time and funds can be commited to the system build. After building a touch screen application in Java that controls a SIRIM system, the code has taken much more time than the hardware build, but it includes more features than is needed for simple process control.

 

[kladue]

Here are a couple general templates for automation system planning, for the hardwarehttp://picasaweb.google.com/kevin.ladue/AutomationTemplates#5474574674613263634 and for the programming http://picasaweb.google.com/kevin.ladue/AutomationTemplates#5474574686684469362These have more than probably is needed so size to fit your needs.