PLC control system design content and design steps - Database & Sql Blog Articles

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1.plc control system design content

(1) According to the design task book, process analysis and determine the control plan, which is the basis of the design.

(2) Select input devices (such as buttons, switches, sensors, etc.) and output devices (such as relays, contactors, indicator lights, etc.).

(3) Select the model of the PLC (including model, capacity, I/O module, power supply, etc.).

(4) Assign the I/O point of the PLC and draw the I/O hardware wiring diagram of the PLC.

(5) Write the program and debug.

(6) Design the control console, electrical control cabinet, etc. and installation wiring diagram.

(7) Write the design manual and the instruction manual.

2. Design steps

(1) Process analysis

In-depth understanding of the process, work characteristics, control requirements of the control object, and divide the various stages of control, summarizing the characteristics of each stage, and the transition conditions between the stages, draw a control flow chart or functional flow chart.

(2) Select the appropriate PLC type

When selecting a PLC model, the following points are mainly considered:

1 function selection. For small PLCs, I/O expansion modules, A/D and D/A modules, and command functions (such as interrupts, PIDs, etc.) are mainly considered.

Determination of 2I/O points. Count the number of I/O points of the controlled system's switching and analog quantities, and consider the subsequent expansion (generally plus 10% to 20% of the spare amount) to select the PLC's I/O points and output specifications.

3 memory estimates. The memory capacity required by the user program is mainly related to factors such as the system's I/O points, control requirements, and program structure length. Generally, it can be estimated by the following formula: storage capacity = number of switching input points × 10 + number of switching output points × 8 + number of analog channels × 100 + number of timers / counters × number of 2+ communication interfaces × 300 + spare amount.

(3) Assign I/O points. Assign the input/output points of the PLC, write the input/output distribution table or draw the wiring diagram of the input/output terminals, and then you can carry out PLC programming and design and on-site construction of the control cabinet or console.

(4) Programming. For more complex control systems, according to the production process requirements, draw a control flow chart or functional flow chart, then design a ladder diagram, then write a statement list program according to the ladder diagram, simulate debugging and modification of the program until the control requirements are met. until.

(5) Design and on-site construction of the control cabinet or console. Design the electrical layout and installation wiring diagram of the control cabinet and the operation console; design the electrical interlock diagram of each part of the control system; perform on-site wiring according to the drawings and check.

(6) Overall debugging of the application system. If the control system consists of several parts, it should be partially debugged before the overall debugging; if the control program has more steps, it can be segmented and then connected.

(7) Prepare technical documents. The technical documentation shall include: electrical drawings such as external wiring diagrams of the programmable controller, electrical layout drawings, electrical component schedules, sequential functional diagrams, ladder diagrams with annotations and instructions.