The most appropriate application for PLCs in process plant is on the packaging lines where high speed discrete control and synchronized motor drives are required. The following can be used as a guideline for those who are considering PLCs on the process side:
• Future growth at the site- will the site is growing in size or scope? If so, it is much easier to expand DCS architecture than PLC architecture while still keeping one integrated control system.
• Need to make change frequently- Does the user need to modify control logic or graphic frequently? These tasks are easier to do with a DCS and can be done while the system is running so there’s no need to stop the controller to add new logic.
• Integration requirements- what are the needs around workflow of operators and control engineers? Do they need access to history, alarms, live trends, live view of control strategies, system diagnostics, etc? These are built in to Experian PKS environment. Also, integration of other systems (PLC, SCADA, etc), devices, applications the enterprise? These can all be more tightly integrated with a DCS and with less engineering.
• Robustness- PLC controllers are very robust, the concern is at the HMI/application/engineering layer. What is the tolerance for loss of view, loss of data, downtime associated with servers/HMI/applications?
• Network – What are the networking skills of the plant folks? Setup and configuration of the network are designed into Experian PKS as a part of plant network environment. Compatibility of various components are tracked and tested, patches are tracked and tested, etc, making the network maintenance load much simpler than a PLC system.