A PLC program is a set of instructions that control a physical process or machine using a programmable logic controller (PLC). A functional specification is a document that describes the requirements, inputs, outputs, logic, and behavior of the PLC program. In this article, you will learn how to create a PLC program from a functional specification in six steps.
The first step is to analyze the functional specification and understand the purpose, scope, and details of the PLC program. You should identify the main functions, features, and components of the process or machine, as well as the inputs, outputs, and parameters of the PLC. You should also note any assumptions, constraints, or special conditions that affect the PLC program.
Whenever I have a functional specification document, I review it thoroughly and divide the required logic into categories I.e. error handling, screen management, production mode, test mode, homing sequence etc. The next step is to document all the required inputs and outputs. Design the control system I.e. electrical diagram. Start coding according to the categories you have made. The most important thing is coordination and collaboration with the stakeholder throught the process to avoid misunderstanding.
The second step is to design the program structure and decide how to organize the PLC program into blocks, routines, and tags. You should follow the programming standards and conventions of your PLC platform and use a consistent naming scheme for your variables and functions. You should also consider the readability, modularity, and maintainability of your PLC program.
The third step is to implement the program logic and write the code that executes the functions and features of the PLC program. You should use the appropriate programming language and tools for your PLC platform, such as ladder logic, function block diagram, structured text, or sequential function chart. You should also test and debug your code as you go along and make sure it matches the functional specification.
The fourth step is to document the program and provide clear and comprehensive information about the PLC program. You should include comments, descriptions, and annotations in your code to explain the purpose, logic, and parameters of each block, routine, and tag. You should also create a user manual, a data sheet, and a flow chart that describe the functionality, operation, and troubleshooting of the PLC program.
The fifth step is to simulate the program and verify that the PLC program works as expected in a virtual environment. You should use a PLC simulator software or a built-in simulator feature of your PLC platform to test the PLC program without connecting it to the actual process or machine. You should check the inputs, outputs, and logic of the PLC program and look for any errors, bugs, or discrepancies.
The sixth and final step is to deploy the program and transfer the PLC program to the physical PLC device. You should use a PLC programming software or a communication cable to download the PLC program from your computer to the PLC memory. You should also connect the PLC to the process or machine and monitor its performance and behavior. You should make any adjustments or modifications as needed and ensure that the PLC program meets the functional specification.