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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →In a typical three-wire DC sensor, a PNP output sources positive voltage to the load, while an NPN output sinks current toward 0 V. That means a PNP sensor normally pairs with a sinking PLC input, and an NPN sensor with a sourcing PLC input. Check the PLC input module’s wiring diagram and the sensor datasheet before connecting or replacing a sensor.
PNP vs. NPN at a glance
| Feature | PNP | NPN |
|---|---|---|
| What the active output does | Supplies positive voltage to the load | Pulls the load toward 0 V |
| Typical PLC input pairing | Sinking input | Sourcing input |
| Load connection | Between the sensor output and the negative rail | Between the positive rail and the sensor output |
| Normally open or normally closed | Either | Either |
| Regional usage tendency described by Balluff | Common in Europe and North America | Common in Asia |
The regional usage descriptions are tendencies, not rules for choosing a sensor. Use the PLC module’s specified input type.
What do PNP and NPN mean on a sensor?
PNP and NPN describe the arrangement and polarity of the sensor’s output transistor. A bipolar transistor has three semiconductor regions; Toshiba’s transistor reference explains the opposite NPN and PNP arrangements and their operating polarity.
In common three-wire DC sensor terminology, the output stage determines what happens on the signal wire when the sensor switches on: PNP supplies positive voltage, and NPN provides a path toward 0 V. Schneider Electric summarizes the distinction as “PNP type: switching on the positive voltage load” and “NPN type: switching on the negative voltage load” in its sensor-output wiring FAQ.
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- Detectable object: magnetic metal [iron, iron alloy, nickel, etc.] (non-magnetic metal has a short detection distance)
- Hysteresis: less than 10% of the working distance (for standard detection objects)
- Power supply voltage: 12~24V DC±10%
- Current consumption: 15mA or less
- Control output: Load power supply voltage below DC26.4V, load current below 100mA, open collector output (NPN/PNP output varies according to the model)
How to wire a three-wire PNP or NPN sensor
Typical DC sensors use brown for the positive supply, blue for 0 V, and black for the switched output. Wire colors and connector pin assignments can vary, so confirm them in the exact sensor datasheet.
PNP sensor
Connect the load or PLC input between the sensor’s switched output and the negative rail (0 V). When active, the PNP output supplies positive voltage through the load. This is why it normally works with a sinking PLC input, which provides the return path for current.
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- Inductive Proximity Switch Type: SN04-P, 3 Wire PNP NO. Detecting Distance: 4mm. Supply Voltage: 5-30VDC, Current Output: 300mA.
- LED working indicator: signal indicator, when sensing metal objects the light is on for normally open, the light is off for normally closed.
- Wiring Method: Brown connect to Positive, Blue connect to Negative, Black connect to Load (signal output).
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- You will get 4pcs SN04-P inductive proximity switch + 4pcs SN Bracket
NPN sensor
Connect the load or PLC input between the positive rail and the sensor’s switched output. When active, the NPN output pulls the signal toward 0 V. It normally works with a sourcing PLC input, which supplies current to the input circuit.
These are typical arrangements, not substitutes for the module’s wiring diagram. Schneider Electric cautions that the sensor output type must match the PLC input card and its wiring.
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- Inductive proximity sensor detects, without contact, a metal object within its magnetic field to count or monitor
- Metal 30-mm tubular body is flush mountable and offers multiple functions for use with various applications
- Sensor has 2-wire AC/DC wiring for PNP or NPN input, a normally open (NO) contact output, and a 2-m electrical cable
- Package Dimensions: 13.208 L x 4.318 H x 9.398 W (centimeters)
Is PNP sourcing or sinking?
A PNP sensor output is sourcing: when active, it supplies positive voltage to the load. Its usual PLC partner is a sinking input, which completes the current path toward 0 V.
An NPN sensor output is sinking: when active, it pulls the load toward 0 V. Its usual PLC partner is a sourcing input, which supplies current from the positive rail. “Sourcing” and “sinking” describe current-path roles; they do not mean the sensor and input should have the same label.
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- Input pulse signal: NPN/PNP open collector ,contact switch, contactless switch, level pulse
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PNP/NPN and NO/NC are different choices
PNP or NPN identifies the output transistor topology; NO (normally open) or NC (normally closed) describes the output’s switching state relative to the sensor’s unactuated condition. A sensor can be PNP NO, PNP NC, NPN NO, or NPN NC. Check both properties in the datasheet rather than inferring one from the other.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Can you replace an NPN sensor with a PNP sensor?
Not automatically. The PLC input circuit must accept the replacement sensor’s output type, and the replacement must also meet the application’s electrical and mechanical requirements.
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- Confirm whether the PLC input module requires a sourcing or sinking sensor output; follow its wiring diagram.
- Check the sensor supply voltage and output-current rating.
- Verify sensing distance, connector and pinout, and environmental rating.
- Confirm the required NO or NC switching behavior separately from PNP or NPN.
A replacement with the wrong output type may not register at the PLC even if it physically fits and its indicator LED turns on.
If the sensor LED is on but the PLC input is not
Before replacing the sensor, check the electrical path from the output through the PLC input:
- Verify that the input card’s sourcing or sinking class is compatible with the sensor output.
- Check the input common and reference wiring against the module diagram.
- Confirm supply polarity and the sensor’s brown, blue, and output-wire connections against its datasheet.
- Check that the sensor’s NO/NC behavior matches the expected switching condition.
A lit sensor LED does not establish that the PLC input wiring or output type is compatible.
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