Design of PLC control system and debug steps

(A) analysis of controlled objects control requirements and


Detailed analysis of control processes and characteristics about control of interaction between mechanical, electrical, fluid, made the control requires control of PLC control system, identification of programmes, development proposal.


(B) determine the input/output devices


According to the system requirements, and determine all of the required input devices (such as push button, position switches, switches and sensors, and so on) and output devices (such as contactors, solenoid valves, signal lights, and other devices, and so on) to determine the associated with the PLC input/output devices, to determine the PLC I/O points.


(C) select PLC


PLC selection including the PLC model, capacity, I/O modules, power supplies and other options, as described in section II of this chapter.


(D) allocation of design PLC I/O and peripheral hardware lines


1. allocation of I/O points


Draw the PLC I/O points corresponding to the connection diagram input/output devices, or relational tables, which can be carried out in the 2nd step.


2. PLC peripheral hardware circuit design


Draw the electrical wiring diagram for other parts of the system, including the main circuit and do not enter the PLC control circuit and so on.


By the PLC I/O connection diagrams and PLC peripheral electrical wiring diagram the electrical schematics of the system. End system hardware circuit has been identified.


(E) programming


1. program design


According to the system requirements, using appropriate design methods to design the PLC program. Procedures to control to meet the system requirements as the main line, write the control functions or tasks one by one program, gradually improved the system to the specified function. In addition, programs should also include the following:


1) initialization program. PLC poweron, are generally required to do some initialization operations, to start the necessary preparations to avoid malfunction of the system. Initializes the main elements of the program are: to clear certain data, counters and other, to restore some data requirements data, to set or reset certain relays, to display certain initial state, and so on.


2) detection and trouble diagnosis and display program. These programs are relatively independent, generally when the program is completed, adding.


3) protection and linkage programs. Protection and chain are indispensable parts of the program, must be seriously considered. It can avoid the control logic confused due to illegal actions.


2. program debugging


Program the basic idea of staging is to facilitate simulations in the form of actual state, to run programs to create the necessary conditions. According to the signal in different ways, staging a hardware simulation and software simulations in two forms.


1) hardware simulation method is to use a hardware device (such as a PLC or other input device, and so on) simulate signals, and these signals to hard wire connected to the input of the PLC system, its effectiveness is stronger.


2) software in PLC, the modeling method is writing a simulation program, analog provide local signals, its simple, but time is not easy to ensure. In the staging process, methods that can be used to debug and program monitoring function.


(F) the hardware implementation


Hardware implementation is mainly to control cabinet (set), such as hardware design and field construction. Main content:


1) designing control cabinets and floor plan and console and other parts of the electrical installation wiring diagram.


2) design the electrical interconnection between the different parts of the system.


3) according to the construction drawings for field wiring, and to conduct an examination.


Due to programming and hardware implementation may simultaneously carry on, so can shorten the design cycle of PLC control system.


(G) debugging


Debugging is to further online tracking through the staging process. Debugging process should be gradual, from the PLC connected input device, and then connect the output device, and then connect to the actual load step by step debugging. If you do not meet the requirements, then adjust hardware and programs. Often only part of the program.


After the full commissioning, delivery operation. After a period of time, if working properly, the program does not need to be modified, procedures should be cured in the EPROM, in case the program is missing.


(H) the collation and preparation of technical documents


Technical documentation including design specifications, hardware schematics, wiring diagrams, electrical components, PLC program, and use the schedule description
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