There are two common types of sensor switches: NPN type and PNP type, so what are the differences and differences between them?
For example, there is a switch VT in the NPN type open collector output circuit, and the output OUT is connected to the power supply 0V through the switch VT, and when the main circuit has a trigger signal, the switch tube is full of conduction, that is, the output OUT and the power supply 0V are connected. For example, PNP type collector electrode open circuit output circuit also has switch tube VT, and its output circuit OUT is connected to power supply +V through switch tube VT, when the main circuit has a trigger signal, the switch tube is full of conduction, that is, the output end OUT and power supply +V are connected. From the above, it can be seen that the NPN type and PNP type sensors have a low level output (0V) and the latter a high level output (+V).
In general, when the PLC is connected to the proximity switch, although the wiring is only brief, it is necessary to distinguish the proximity switch of the NPN type and the PNP type sensor in the specific use. The PLC we use is divided into European and Japanese, the switching module of the European PLC is mostly a source input circuit, and the switching module of the Japanese PLC is mostly a leaky input circuit.
Therefore, the source input circuit is actually from the point of view of the terminal block of the switching module, because there are input terminals and common terminals. In the case of source input circuits, current flows from the common terminal and then from the input terminal. The terminal blocks of the switch star module of the leakage input circuit also have a common terminal and an input terminal, and the current flows out of the input terminal and flows in from the common terminal for the leakage input circuit.
Therefore, when the switch star module of the PLC is connected to the close switch, it is a Japanese PLC such as Mitsubishi and Omron, and the input terminal of the switch star module is the current outflow, which should be connected to the low-level output close to the switch, that is, the NPN type sensor. It is a European PLC such as Siemens, and the input end of its switching module is current flowing, and it should be connected to a high-level output close to the switch, that is, a PNP sensor. All in all, look at the current at the input end of the PLC switch star module from which it flows in or out, so as to choose the kind of close switch connection.
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