Six types of pnp and npn sensors (switch type)
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Six types of pnp and npn sensors (switch type)

Posted Date: 2024-02-04

The pnp and npn types actually use saturation and cutoff to output two states, and are switch-type sensors. But the output signals are completely opposite, that is, high level and low level. The output of pnp is low level 0, and the output of npn is high level 1.

Pnp and npn type sensors (switch type) are divided into six categories:

1. npn-no (normally open type)

2. npn-nc (normally closed type)

3. npn-nc+no (normally open and normally closed common type)

4. pnp-no (normally open type)

5. pnp-nc (normally closed type)

6. pnp-nc+no (normally open and normally closed common type)

PNP and NPN type sensors generally have three lead-out lines, namely power line vcc, 0v line, and out signal output line.

1. npn class

npn means that when a signal is triggered, the signal output line out is connected to the power line vcc, which is equivalent to a power line that outputs a high level. For the npn-no type, when there is no signal trigger, the output line is floating, that is, the vcc power line and the out line are disconnected. When a signal is triggered, the same voltage as the vcc power line is emitted, that is, the out line is connected to the power line vcc, and a high level vcc is output.

For the npn-nc type, when there is no signal trigger, the same voltage as the vcc power line is emitted, that is, the out line is connected to the power line vcc, and a high level vcc is output. When a signal is triggered, the output line is floating, that is, the vcc power line and the out line are disconnected. For the npn-nc+no type, there is actually one more output line out, which can be chosen according to needs.

2. pnp class

pnp means that when a signal is triggered, the signal output line out and the 0v line are connected, which is equivalent to outputting a low level, 0v. For the pnp-no type, when there is no signal trigger, the output line is floating, that is, the 0v line and the out line are disconnected. When a signal is triggered, the same voltage as 0v is emitted, that is, the out line is connected to the 0v line, and the output output is low level 0v. For the pnp-nc type, when there is no signal trigger, the same voltage as the 0v line is emitted, that is, the out line is connected to the 0v line, and a low level 0v is output. When a signal is triggered, the output line is suspended, that is, the 0v line and the out line are disconnected. For the pnp-nc+no type, it is similar to the npn-nc+no type, with one more output line out and two output lines with inverted signals, which can be selected according to needs. What we generally use is the npn type, which is the high-level active state. pnp is rarely used.

First find the power terminal and output terminal of the proximity switch. If it is a two-wire system, there should be a +vdc terminal, output terminal) or a "-" terminal! For source input plcs such as Modicon, Siemens, etc. (check which plc you use), you can connect the +24v sensor power supply that comes with the plc to the +vdc end! The output terminal of the proximity switch can be connected to the input terminal of the plc! For source input plc, once the switch is close to the action, the plc input terminal will get a DC voltage that is slightly smaller than the plc sensor power supply, thus making the plc switch input valid! For PLCs such as Mitsubishi, since it receives a leaky input, the proximity terminal should be connected to the input terminal (such as x10), and the output (or the "-" terminal should be connected to the power ground terminal. Once the proximity switch operates, the proximity switch output becomes low (or close to ground potential), which makes the plc input valid! The three-wire proximity switch must be connected to the positive power supply and ground terminal of the sensor!

The sensor power supply must be the same power supply as the proximity switch power supply or there should be current to form a loop to work! There is no need to distinguish Mitsubishi, because its switching input already has its own power supply! Note: Although some proximity switches are two-wire, they have three wires, one of which is a shielded wire, which should be distinguished!

Review Editor: Huang Fei


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