The switch input module is used to receive switch signals from on-site input devices, convert the signals into low-voltage signals received internally by the PLC, and achieve electrical isolation between internal and external signals of the PLC. When making a choice, the following aspects should be considered:
1) Type and voltage level of input signal
There are three types of switch input modules: DC input, AC input, and AC/DC input. The selection is mainly based on on-site input signals and surrounding environmental factors. The delay time of the DC input module is relatively short, and it can also be directly connected to electronic input devices such as proximity switches and photoelectric switches; The communication input module has good reliability and is suitable for use in harsh environments with oil mist and dust.
The voltage levels of the input signal of the switch input module include DC 5V, 12V, 24V, 48V, 60V, etc; Exchange 110V, 220V, etc. The selection is mainly based on the distance between the on-site input device and the input module. Words? V. 12V and 24V are used for transmission distances that are relatively close, such as 5V input modules, which should not exceed a maximum distance of 10 meters. Modules with higher input voltage levels should be selected for those that are far away.
2) Input wiring method
The switch input module mainly has two wiring methods: junction type and group type,
All input points of the switch type input module share a common terminal (COM); The grouped switch input module divides the input points into several groups, each group (several input points) has a common terminal, and the groups are separated from each other. The price of grouped switch input modules is higher than that of sink type. If there is no need to separate input signals, sink type is generally selected.
3) Pay attention to the number of input points connected simultaneously
For selecting high-density input modules (such as 32 point, 48 point, etc.), it should be considered that the number of points that the module is connected to at the same time should generally not exceed 60% of the input points.
4) Input threshold level
In order to improve the reliability of the system, the size of the input threshold level must be considered. The higher the threshold level, the stronger the anti-interference ability and the farther the transmission distance.
