Detailed steps for PLC system design and commissioning - Database & Sql Blog Articles

(1) Analyze the controlled object and propose control requirements

A thorough analysis of the process and working characteristics of the controlled object is essential to understand how the machine, electrical system, and fluid components interact. Based on this understanding, specific control requirements for the PLC system are defined. This step also involves determining the overall control strategy and preparing a detailed design task specification.

(2) Determine input/output devices

Based on the system's control needs, all necessary input devices such as buttons, position switches, transfer switches, and sensors are identified, along with output devices like contactors, solenoid valves, and signal indicators. This helps in determining which I/O points will be connected to the PLC, ensuring proper configuration for system operation.

(3) Choose PLC

Selecting an appropriate PLC involves choosing the right model, capacity, I/O modules, and power supply. The selection should align with the system's functional and performance requirements. For more details, refer to Section 2 of this chapter.

(4) Allocate I/O points and design PLC peripheral hardware circuits

1. Assign I/O points

Create a connection diagram or mapping table between the PLC's I/O points and the corresponding input/output devices. This can also be done during the earlier stage of device selection.

2. Design the peripheral hardware circuit

Draw the electrical schematic for the rest of the system, including both the main circuit and the control circuit that does not interface directly with the PLC. Once completed, the entire system’s hardware layout is fully determined.

(5) Program design

Programming

Based on the system’s control requirements, the PLC program is developed using suitable design techniques. The program must meet the system’s control functions and be structured to implement each sub-task systematically. In addition, the program typically includes:

A. Initialization procedures. After power-on, certain initialization steps are needed to prepare the system for operation, avoiding potential malfunctions. These include clearing data areas, resetting counters, restoring required data, and setting initial states.

B. Detection, fault diagnosis, and display routines. These are usually added later in the development process and operate independently.

C. Protection and interlock procedures. These are crucial for preventing logic errors caused by unauthorized operations, ensuring safe and stable system behavior.

2. Program simulation and debugging

Simulation debugging aims to replicate real-world conditions in a controlled environment. There are two common methods: hardware simulation and software simulation.

A. Hardware simulation uses external devices like another PLC or input modules to generate signals that are connected directly to the PLC inputs, offering better real-time performance.

B. Software simulation involves writing a separate program within the PLC to simulate field signals. It is easier to implement but may have limitations in timing accuracy. Segmented debugging and the use of programmer monitoring tools can help improve efficiency.

(6) Hardware implementation

This step focuses on designing and installing the physical components such as control panels and cabinets. Key tasks include:

A. Drawing up the layout and wiring diagrams for the control cabinet and console.

B. Creating interconnection diagrams between different parts of the system.

C. Performing on-site wiring according to the plans and conducting thorough inspections.

Since programming and hardware work can be done in parallel, the overall project timeline is significantly reduced.

(7) Online debugging

Online debugging involves fine-tuning the program after it has been simulated. It should be conducted step by step, starting with input devices, then output devices, and finally the actual load. Adjustments to both hardware and software may be required if the system doesn't perform as expected. Usually, only minor program changes are needed.

After full testing and successful operation, the program is finalized and stored in EPROM to prevent data loss.

(8) Organize and write technical documentation

Technical documentation includes design specifications, hardware schematics, installation wiring diagrams, component lists, PLC programs, and user manuals. These documents ensure clarity and support for future maintenance and system upgrades.