When starting a new controls project, it’s important to know what you don’t know in terms of process control and hardware component control (electrical & mechanical) that your controls system is controlling and the limitations of both the process and the hardware.
First, it is important to develop a gap analysis or preliminary requirements from the stake holders such as the customer or internal customer starting from the component level design & control, working to the process and higher-level control design where multiple hardware components are controlled in parallel. This design process is called the bottom-up or inside-out design approach. This design approach is somewhat time consuming initially but allows the controls engineers as well as the mechanical/electrical design engineers to have a better understanding of the process and hardware. Then one can create a formal functional requirements document listing out the tasks to control each individual hardware component and later the design of the process or overall motion control. This formal Functional Requirements Document (FRD) will have control tasks associated with each requirement. The requirement section can be tied to tasks in MS Project Management or Jira. One can determine what tasks can be developed in parallel and which can be done sequential. From there it is a matter of creating sprints or time intervals where a group of tasks can be completed during this time interval within the controls engineering team. Having a formal functional requirements document is important as it is the road map for your control system product. It is important to allow for expandability for both controls hardware and software (via OOP), redundancy for mission critical sensors and actuators, and keeping things as simple as possible reducing software and hardware complexity which allows for better control code troubleshooting and maintenance. Once the FRD is completed, then you can start selecting your sensors and actuators. Design the external sensor and actuator interface schematics which tie into you proposed PLC IO rack. Next, design your PLC IO rack based on PLC bus & sensor/actuator power consumption. Add and link your PLC IO control variables to the IO modules in your PLC IO tree and create device driver to translate your IO module signal counts to actual physical signals (e.g., pressure, flow, velocity, etc.) and so forth. Then you are off to the races with electrical & mechanical component control and high-level process/motion control!
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AuthorGraham is a control system engineer enthusiastic about controls, design, hockey, and art! Archives
April 2023
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