Key considerations for supporting NPN and PNP proximity switches
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Key considerations for supporting NPN and PNP proximity switches

Posted Date: 2024-01-16

NPN and PNP

Since each company has different definitions of source type, sink type, NPN and PNP, it is easy to be confused when talking about NPN or PNP individually.

Therefore, for the input side only need to determine:

If the common terminal is power supply -, it is a sink input and is connected to a PNP proximity switch;

If the common terminal is power +, it is a source input and is connected to an NPN proximity switch.

For the output side just make sure:

The M (N) terminal is power +, then it is a sink output;

The M (N) terminal is power supply -, which means it is a source output.

Does the S7-300 input module SM321 support connecting NPN and PNP proximity switches?

Most of them are sinking inputs (including 31xC type integrated DI), connected to PNP proximity switches;

Source input: 6ES7321-1BH50-0AA0, connected to NPN proximity switch;

Source/sink input: 6ES7321-1BP00-0AA0

Figure 1 Sink input, connected to PNP proximity switch

Figure 2 Source input, connected to NPN proximity switch

Does the S7-300 output module SM322 support both source and drain?

Most of them are source outputs (including 31xC type integrated DO)

Sink output: 6ES7322-1BP50-0AA0

For specific data of the S7-300 module, please refer to: SIMATIC S7-300 module data

Which modules available for S7-300 systems support NPN and PNP proximity switches?

In addition to what is mentioned in question 1, you can consider using distributed IO modules in distributed IO sites; whether NPN or PNP is supported depends on different models.

For details, please refer to: ET200 selection sample

Can NPN and PNP proximity switches be converted into each other?

It is recommended to use an intermediate relay for conversion; however, for high-speed signals, carefully determine the relay model and use, as it is easy to lose the signal.

Review Editor: Huang Fei


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