Can One Controller Do It All? - 4. Process ControlWritten by Bob Nelson Wednesday, 23 September 2009 00:00
Table of contents
Availability of pre-engineered solutions, templates, and extensive libraries: Process users look to leverage pre-defined objects from libraries (i.e., cascade PID) rather than “rolling their own.” This speeds up configuration and makes the resulting project more consistent and maintainable. It would be advantageous if you could also create your own library objects based on your unique control strategy.
Ability to select program execution speed: The normal reaction to controller speed is “faster is better.” However, for process applications regulatory control loops normally scan in the 100 to 500 millisecond range. In some cases, it could be detrimental to have control logic execute any faster – possibly causing excessive wear on final control elements such as valves, resulting in premature maintenance and process issues. It is important to have the ability to select program execution speed.
Emphasis on design using a top-down approach to engineering: Process users spend a lot of time on up-front design and overall program structure. This focus on upfront design minimizes costs, compresses project schedules and creates applications that can be maintained by plant personnel over the long term. Since many process applications are large and plant-wide in scope, the ability to propagate libraries and templates throughout the application is very important to minimize rework and promote the use of standards.
Ability to be installed in a hostile environment: Many process applications are in hazardous (i.e., explosive) environments. Additionally, the environment may be moist or corrosive, potentially leading to damage of critical electronics. The automation platform and associated peripherals must withstand such environments without undue installation costs or complexity.
Embedded knowledge: Technology is just part of the challenge to produce an effective automation platform for process applications. It helps tremendously if the supplier knows process control and has embedded this knowledge in their technology and the available libraries. The result is a platform designed to meet the unique requirements of process applications “out of the box.”