(1) the analysis of the existing system works
Understand the process of the controlled device and mechanical functioning, according to relay diagram analysis and principle of master control system.
(2) PLC I/O distribution
Determine the system‘s input and output devices, the PLC I/O allocation, draw the PLC wiring diagram.
(3) correspond to the establishment of other components
OK relay diagram relay, time relays, auxiliary relays and timers in the PLC correspondence.
(2) and (3) two steps set up a relay diagram of all the components and PLC programming elements within the relationship, for the purposes of transplantation method, it is very important. In this process should deal with several problems:
1) implementation of components in the circuit of the relay corresponding to the PLC output relays, such as AC and DC contactors, solenoid valves, solenoid, lights, etc.
2) master in electrical relay circuits corresponding to the PLC input relay, such as button, position switches, selector switch, etc. Thermal relay contacts can be used as input of the PLC can also be connected to the PLC in the external circuit, surplus is mainly look at whether the PLC input points. Notice deal with the PLC internal and external contacts are normally open and normally closed.
3) relay in the circuit relay corresponding to the PLC auxiliary relay.
4) relay in the circuit time relay corresponding to the PLC timer or counter, but be careful, time relays are power–delay and off–delay of the two, while the timer only “power–delay“.
(4) design of ladder diagram programs
According to the correspondence, will relay diagram “translated“ into the corresponding “ladder diagram“, then according to the rules of ladder diagram programming “ladder diagram“ into structured ladder diagrams. For complex control circuits can be classified as zero, partial conversions, finally together again.
(5) proofread carefully, seriously and debugging
Convert ladder make sure you proofread carefully, after serious debugging, in order to ensure its control functions consistent with the original image.
PLC ONE 