In the wiring between PLC module and field equipments, there are usually two connection methods, source type (NPN) and drain type (PNP), which are very important for equipment safety. The following introduce these two connection methods for your reference:
Output of PNP shares the negative pole with the power supply, controls the on-off of the positive pole, and outputs a positive voltage. NPN is on the contrary, its output shares the positive pole with the power supply, controls the on-off of the negative pole, and outputs a negative voltage.
Japanese prefers to use NPN, Europe and America prefer to use PNP. However, most products now support both connection methods. However, generally only one of the input signal types of the same PLC can be selected. For temporary emergency use, a small relay can be used to switch the signal polarity.
Both NPN and PNP sensors use two states of saturation and cut-off of triodes
Take the I/O point as an example, the source type means that the current flows out from the I/O point; the sink type means that the current flows in the I/O point.
NPN: when a signal is triggered, the signal output line OUT and GND are connected, which is equivalent to OUT outputting low level.
PNP: When a signal is triggered, the signal output line OUT and VCC are connected, which is equivalent to OUT outputting a high level.
Output high or low levels are related to working characteristics, and can refer to analog electronic circuits.