Hardware design and software design and debugging of PLC - Database & Sql Blog Articles

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1.plc hardware design

PLC hardware design includes: PLC and peripheral line design, electrical circuit design and anti-interference measures design.

After selecting the PLC model and assigning I/O points, the main content of the hardware design is the design of the schematic diagram of the electrical control system, the selection of electrical control components and the design of the control cabinet. The schematic of the electrical control system includes the main circuit and the control circuit. The control circuit includes the I/O wiring of the PLC and the detailed connection of the automatic and manual parts. The selection of electrical components is mainly based on the selection of buttons, switches, sensors, protective appliances, contactors, indicator lights, solenoid valves, etc. according to control requirements.

2.PLC software design

The software design includes the system initialization program, main program, subroutine, interrupt program, fault emergency measures and auxiliary program design. The small switch quantity control is generally only the main program. First of all, according to the overall requirements and the specific conditions of the control system, determine the basic structure of the program, draw a control flow chart or functional flow chart, simple can be designed with empirical methods, complex systems are generally designed with sequential control design.

3. Debugging of software and hardware

Debugging is divided into analog debugging and online debugging.

After the software is designed, it is usually used for analog debugging. Analog debugging can be debugged on the computer by emulation software instead of PLC hardware. If there is PLC hardware, you can use the small switch and button to simulate the actual input signal of the PLC (such as start and stop signals) or feedback signal (such as the limit switch is turned on or off), and then through the output bits on the output module. The indicator light, observe whether the output signal meets the design requirements. When an analog signal I/O is required, a potentiometer and a multimeter can be used together. In the programming software you can use the state diagram or status diagram to monitor the operation of the program or to force certain programming elements.

The analog debugging of the hardware part is mainly to test the wiring of the control cabinet or the console. The switch input signal outside the PLC or the command switch of the operation button can be simulated on the terminal block of the console to observe the status of the corresponding PLC input point. Use the programming software to forcibly turn ON/OFF the output point, observe whether the PLC load (indicator, contactor, etc.) in the corresponding control cabinet is normal, or whether the status of the output signal on the corresponding terminal is changed correctly.

When debugging online, download the programmed program to the PLC in the field. When debugging, the main circuit must be powered off, and only the control circuit is debugged online. Through on-site debugging, you will also find new problems or improvements to certain control functions.