PLC in practical applications often run into two problems: one is the PLC I/O points is not enough and needs to be expanded, however increased I/O points will increase costs; second, the PLC has selected an Extensible I/O points are limited and cannot be increased. Therefore, on the premise of meet the system requirements, the rational use of I/O points to minimize the I/O required points is of great significance. Here‘s some common measures to reduce I/O points.
1. Matrix output
Figure 6-17 matrix 4×4 with 8 outputs, 16 output devices (load). You want a load connected, as long as the control in which it is row and column the corresponding output relay can be connected, for example, to load the KM1, Y0 and Y4 output must be controlled through.
Special attention should be paid: when only a row corresponding to the output relays are connected, each column corresponds to any of the output relay can be connected, or when the corresponding output relay switch on only one column for each row corresponding to any of the output relay can be connected, otherwise an error will occur through the load. Therefore, using matrix outputs, the load must be connected at the same time, in the same row or in the same column, you cannot control.
2. grouped output
When the two sets of output device or load does not work via external switch or by means of a PLC control electrical switch contacts, so each PLC output points can control two different work loads. As shown in Figure 6-18, KM1, KM3, KM5 KM2, KM4, KM6 group does not turn on, switch to switch SA.
Figure 6-18 grouped output
3. the parallel output
When two switching status is identical load, parallel use of PLC outputs. But beware of PLC outputs drive multiple loads at the same time, should consider the adequacy of the PLC output drive capability.
4. output devices multifunction
Using PLC logic functions, an output device for a variety of purposes. For example the relay system, an led indicates a State and PLC systems, is easy to implement with a permanent and flashing the lights output control, so that an led to indicate the two States both led and reduced output points.
5. some output devices may not PLC
Some relatively independent, relatively simple system control section, directly by PLC controlled external hardware circuits.
Some common measures to reduce I/o points, only for reference, practice should be based on specific circumstances, flexible use. Also should be careful not to reduce the I/0 points of PLC, and complicate external additional circuits, thereby affecting the reliability of the system.