Design principles of PLC application system

At present, PLC systems can handle almost all tasks in the field of industrial control, and are most suitable for situations with poor industrial environments, high requirements for safety and reliability, and complex control processes. The following principles should be followed when designing PLC application systems.

(1) Meeting control requirements

The primary premise of designing a control system is to maximize the process requirements of the controlled object. This requires designers to conduct in-depth field investigations and research before designing, collect field data and effective control experience for system design.

(2) Safe and reliable

Whether the control system can be safe, reliable and stable in long-term operation is an important principle in designing the control system. This requires comprehensive consideration in system design, device selection and software programming. For example, in hardware and software design, it should be ensured that the PLC program can not only run correctly under normal conditions, but also run normally under some abnormal conditions (such as sudden power failure and power on, wrong button pressing). The program can accept and only accept legal operations, and can reject illegal operations, etc.

(3) Economical and practical

Under the condition of meeting the control requirements, on the one hand, we should expand the project benefits, and on the other hand, we should pay attention to reducing costs. The design must be reasonable and economical to give full play to the control advantages of the PLC system, which requires the control system to be simple and economical, and easy to use and maintain with low cost.

(4) Adapt to development

When designing a PLC system, it is necessary to consider future functional expansion, which requires that appropriate redundancy be left when selecting PLC models and I/O modules.

Designing a PLC application system mainly includes the following contents:

1) Formulate the technical conditions for control system design, usually in the form of a design brief.

2) Select the electrical transmission form and actuators such as motors and solenoid valves.

3) Select the PLC brand and model.

4) Prepare the PLC's I/O address allocation table or draw the I/O terminal wiring diagram.

5) Write the software specification according to the system design requirements, and then use the corresponding programming language (commonly ladder diagram) to perform program design.

6) Understand and follow user cognitive psychology, attach importance to the design of human-machine interface, and enhance the friendly relationship between people and PLC.

7) Design operating tables, electrical cabinets and non-standard electrical components.

8) Prepare design specifications and operating instructions.

According to the specific design tasks, the above content can be adjusted appropriately.