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

(1) Analyze the controlled object and propose control requirements

Begin by thoroughly analyzing the process and operational characteristics of the system being controlled. Understand how the mechanical, electrical, and fluid components interact. Based on this analysis, define the specific control requirements for the PLC system. This step helps in developing a clear control plan and drafting a detailed design specification.

(2) Determine input/output devices

Identify all necessary input devices such as buttons, limit switches, selector switches, and sensors, as well as output devices like contactors, solenoid valves, and indicators. This helps determine which I/O points will be connected to the PLC, allowing you to calculate the required number of I/O ports.

(3) Select the PLC

Choose an appropriate PLC model based on the system's capacity, I/O module requirements, power supply specifications, and other relevant factors. Refer to section 2 of this chapter for more detailed guidance.

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

1. Assign I/O points: Create a mapping between the PLC’s I/O points and the actual input/output devices. This can also be done during step 2.

2. Design the peripheral hardware: Draw the electrical schematic for the rest of the system, including the main circuit and control circuit not integrated into the PLC. The complete system diagram includes both the PLC I/O connection layout and the peripheral electrical circuits. At this stage, the hardware configuration is finalized.

(5) Program design

Develop the program according to the system’s control requirements using suitable design methods. The program must fulfill the system’s functional needs, implementing each control task step by step. Additionally, the program should typically include:

A. Initialization routines: Upon startup, the PLC usually requires some initialization steps to prepare the system, such as clearing memory areas, resetting counters, setting relays, or displaying initial states.

B. Diagnostic and monitoring procedures: These are often added later in the development cycle and help detect faults or monitor system status.

C. Protection and interlock logic: Essential for ensuring safe operation and preventing errors caused by improper actions.

2. Simulate and debug the program

Simulate the real-world environment to test the program. There are two common simulation methods:

A. Hardware simulation: Use additional devices like another PLC or signal generators to simulate field signals and connect them directly to the PLC inputs. This method offers better real-time performance.

B. Software simulation: Implement a separate simulation program within the PLC to generate the necessary signals. It is easier to implement but may have less real-time accuracy. Segmentation debugging and programmer monitoring tools can be used for better results.

(6) Hardware implementation

Focus on designing and installing the control panel, wiring, and related hardware. Key tasks include:

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

B. Creating the electrical interconnection diagram for the entire system.

C. Performing on-site wiring and conducting thorough inspections.

Since programming and hardware installation can be done in parallel, the overall design time is significantly reduced.

(7) Online debugging

After simulation, perform online testing by connecting the PLC to the actual input and output devices, and then gradually introduce the real load. If the system does not meet expectations, adjust the hardware or modify the program accordingly. Usually, only minor program changes are needed.

Once all tests are complete, the system is ready for operation. After a period of normal use, if no further modifications are needed, the program should be stored in EPROM to prevent data loss.

(8) Organize and write technical documentation

Prepare comprehensive technical documents, including design specifications, hardware schematics, installation wiring diagrams, component lists, PLC programs, and user manuals. These documents ensure clarity and ease of maintenance for future reference.