Conversion design method of relay diagram is converted with the original function within the same PLC ladder diagrams. This equivalent conversion is a simple shortcut of programming method, conversion method of advantages many, one, original following electrical control system after long-term using and test, has was proved can completed system requirements of control function; second, following electrical circuit diagram and PLC of trapezoidal figure in said method and analysis method Shang has many similar of at, so according to following electrical circuit diagram to design trapezoidal figure simple shortcut; its three, this design method General not need changes Control Panel, keep has original system of external characteristics, Operators do not have to change longstanding habits.
1. Basic methods
According to the circuit diagram of relay contactor to when designing PLC ladder diagram, the key is to catch them one by one, namely corresponding to control functions, logic functions, hardware components and software for PLC and relay components.
2. Conversion design steps
① understand and become familiar with the controlled device process and mechanical functioning, according to relay diagram analysis and principle of master control system, so that you can know when designing and debugging the system.
Determining PLC input and output signals, draw the external wiring diagram of PLC.
Relay diagram for AC contactors and electromagnetic valve actuators use PLC output relay to replace their hardware coil connected to the outputs of the PLC. Button switches, limit switches, proximity switches and control switch replaced by a PLC input relay, used to provide control and feedback signals to the PLC, their contacts are connected to the input of the PLC. In the determination of the input of the PLC signal corresponding input and output signal relay component and output relay number, draw the external wiring diagram of PLC.
③ determine of PLC ladder diagram auxiliary relay (m) and the timer (t) components.
Relay diagram relay time relay function using PLC auxiliary relay and timer in place, and define their relationship.
According to the corresponding relations draw a ladder diagram of PLC.
Second and third step set up a relay diagram of hardware components and relationship between software components in a ladder diagram, ladder diagram relay diagram into corresponds.
II according to the controlled device process and mechanical movements and basic rules of ladder diagram programming, optimization of ladder diagram, ladder diagram is consistent with control requirements, and with rationality, order and reliability.
⑥ ladder diagram write according to their corresponding instruction list.
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