Design of PLC control system the main steps to be followed and the content

(1) technical analysis
In-depth understanding of process control object, features, requirements, and dividing control of all phases, summarized the various stages of, and between the various stages of transition conditions, draw the flowchart control flow chart or function.
(2) select the appropriate PLC type
When you select the PLC model, mainly consider the following points:
 1 choice of functions. For small PLC main I/O expansion module, a/d and d/a modules and features of the directive (such as interrupt, PID, etc).
 2 I/O number to determine. Statistical control system switches, analog I/O point numbers, and consider future expansion (General plus 10%~20% spare capacity), to choose the PLC I/O points and output specifications.
 3 memory estimate. User program memory required is mainly with the system‘s I/O points and control requirements, length of program structure and other factors. General estimation according to the following formula: storage capacity = switch input points x8+ points X10+ switch output analog channel number x100+ number x300+ number X2+ communications interface standby timer/counter.
(3) allocation of I/O points. Distribution PLC input/output points, write input/output allocation table or input/output terminals the wiring diagram, and PLC programming, both control cabinet or console design and field construction.
(4) program. For more complex control systems, according to the production requirements, draw the flowchart control flow chart or function, and then design a ladder diagram, again according to the prepared statement form the ladder program, staging and modifications to the program, up until the requirement is met.
(5) the controller or console design and field construction. Designing control cabinets and work station layout and installation of electric wiring diagram; design components of the control system of the electrical interlock diagram according to drawings for field wiring and check.
(6) using the integrated debugging. If the control system consists of several components, you should first make a local debugging, and make the whole debugging; more if you control the sequence, the segment can be debugged, and then dispatching and connected.
(7) prepare technical documents. Technical papers should include: programmable controllers wiring diagram electrical engineering, electrical layout, electrical component breakdown, sequential function chart, ladder diagram with notes and descriptions.

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