What is the difference between the source type and the sink type of Siemens PLC modules?

Q: When using Siemens modules, I often encounter two types of modules: active and leakage. Also, what are the differences between the relay type modules?

Answer: 1. Source type (source), the current flows out from the terminal, with the output characteristics of a PNP transistor; sink type (sink), the current flows into the terminal, with the output characteristics of an NPN transistor.

The so-called "leakage input" is an input form in which the input signal source is provided by the PLC internally, and one end of all input signals is aggregated to the input common connection terminal COM. It is also called "sink input". When the input sensor is a proximity switch, as long as the output driving force of the proximity switch is sufficient, the PLC input terminal of the leakage input can be directly connected to the output of the npn open collector proximity switch.

The so-called "source input" is an input signal power supply provided by the outside or the power supply provided to the input circuit by the PLC. All input signals are "active" signals and are independently input to the PLC. When the input sensor is a proximity switch, as long as the output driving force of the proximity switch is sufficient, the PLC input terminal of the source input can be directly connected to the output of the PNP open collector proximity switch.

2. S7-200 PLC can be connected to either sink type or source type, while 300 PLC is generally source type. Europe and the United States are generally source type, and the input generally uses a pnp switch, which is a high-level input. Japan and South Korea prefer sink type, and generally use an npn switch, which is a low-level input.

3. Source output means the output is the positive DC pole, and sink output means the output is the negative DC pole. So Siemens PLC output has both source and sink output, but it is generally source type.

4. Mitsubishi PLC has both source and sink inputs, but most of them are sink inputs. The proximity switch corresponding to the sink input is NPN type.