The PLC Pro Tutorial Framework
PLC Pro Tutorials follow a common example application through the activities required to develop its control system. The work begins by defining what the customer needs the equipment to accomplish, then follows the application through the design and programming considerations addressed by PLC Pro Methods.
Define the Customer Need
Whenever practical, the PLC Pro should participate early enough in the design process to understand the customer’s requirements and contribute controls-related considerations, including control architecture and component selection, before the equipment design is finalized.
Whether or not the PLC Pro participates in the equipment design, the customer’s expectations, requirements, standards, and operating constraints must be understood before the control program is developed.
That understanding must be translated into application-specific requirements, guidelines, and measurable criteria that can guide development and later be used to evaluate the completed solution.
Develop the IO Schedule
Before useful PLC programming can begin, the PLC Pro must determine how the control program will direct, coordinate, and verify the equipment actions required by the application. The IO Schedule is the working product of that controls-oriented review of the equipment design. In it, the PLC Pro will identify the sensors, actuators, drives, safety interfaces, communications, and other devices or systems the control program has available to get the job done.
The resulting IO Schedule is broader than a list of discrete inputs and outputs. It identifies the actual PLC interfaces to the equipment and surrounding systems, including physical IO, intelligent devices and communications data, together with the information needed to locate and use each interface in the control program.
The IO Schedule remains with the equipment throughout its service life. During development and commissioning it is maintained as the programmer's current working reference, and after commissioning it becomes a primary maintenance document for understanding the control system and locating its interfaces. Whenever wiring, hardware, addresses, devices, or communications interfaces change, the schedule is updated to reflect the equipment as it actually exists.
Map the IO
With the workstation IO identified and documented in the IO Schedule, the PLC Pro can establish the program interface between the physical IO and the internal variables used by the control application. IO Mapping provides that defined interface for both inputs and outputs.
This separation keeps physical IO addresses out of the workstation control logic. Hardware changes can therefore be accommodated in the mapping without chasing address references throughout the program, while the organized mapping provides maintenance and troubleshooting personnel a predictable place to relate program variables to the actual workstation IO.