FX series PLC ladder diagram programming elements names letters and digits, they represent the type of component and the component number, such as Y10,M129. Input relay output relay element, represented by the octal number, octal number only 0~7 the 8 digit symbol, follow the “every 8 into 1“ operation. For example, octal, X17 and X20 are two adjacent integers. Table 3–3 shows the FX2N series PLC input/output relay components.
1. Enter a relay (x)
Enter relay is the digital signals of PLC receives external input window. PLC optical Coupler, to read external signals into registers and stored in the input image. Input an external normally open or normally closed contacts, or series-parallel circuit consisting of multiple contact points or electronic sensors (proximity switches). In a ladder diagram, can be used multiple times to enter relay normally open contact and a normally closed contact.
Figure 3–6 shows a diagram of the PLC control system, X0 Terminal input of the external circuit is switched on, the input image register–1 status to which it corresponds, disconnected to a 0 State. Enter the relay status depends only on external input signal status, it is not possible under the control of the user program, and must not appear in a ladder diagram enter the relay‘s coil.
Because PLC is read at the beginning of each scan cycle time of the input signal, the input signal is ON or OFF duration should be greater than the PLC scanning cycle. If this condition is not met, input signal may be lost.
2. output relay (Y)
Output relay is the PLC sends signals to the external load window. Output relay output signal to PLc
To the output module, which then drive the external load. If the coil of ladder diagram in Figure 3-6 Y4 “power on“, relay output modules corresponding to the hardware relay normally open contact is closed, the external load work. Each hardware module relay output only a pair of constant open contacts, but in a ladder diagram, each output relay normally open and normally closed contacts can be used more than once.
PLC ONE 