Why Output Type Matters
When selecting a proximity sensor, the output must match the device receiving its signal. A sensor may detect the target correctly but still fail to communicate with the controller if the electrical interface is incompatible.
NPN and PNP describe two common transistor output types. The explanation below applies to typical three-wire DC sensors.
How an NPN Output Works
An NPN output sinks current. When the output turns on, current flows from the positive supply, through the load or input circuit, and into the sensor output toward 0 V.
The load is connected between the positive supply and the sensor output.
How a PNP Output Works
A PNP output sources current. When the output turns on, current flows from the sensor output through the load or input circuit toward 0 V.
The load is connected between the sensor output and the negative supply.
| Feature | NPN Output | PNP Output |
|---|---|---|
| Output function | Sinks current | Sources current |
| Load connection | Between supply positive and output | Between output and 0 V |
| Typical compatible PLC input | Sourcing input | Sinking input |
Check the controller’s wiring diagram to confirm compatibility. Some input modules support both arrangements, depending on how they are wired.
NPN and PNP Are Different from NO and NC
NPN or PNP describes the electrical output arrangement. Normally open or normally closed describes when the output switches.
- Normally Open (NO): The output turns on when a target is detected.
- Normally Closed (NC): The output is on when no target is detected and turns off when a target is detected.
These are separate choices. A sensor may be specified as NPN NO, NPN NC, PNP NO, or PNP NC, depending on the model.
Selecting a Sensor for Your Equipment
Start with the controller or PLC input documentation. Confirm the required output type and follow the specified connection diagram.
Next, check the exact sensor model for:
- Supply voltage compatibility.
- NO or NC switching operation.
- Output current rating and input electrical requirements.
- Cable or connector pin assignments.
When replacing a sensor, record the full model number and existing wiring before choosing a replacement. Matching the housing size and sensing distance alone is not enough.
Disconnect power before wiring, and use the model-specific diagram rather than assuming that all sensors share the same connections.
Get Help Confirming Compatibility
Send YPROX your existing sensor model, controller input specifications, or wiring diagram, together with your detection requirements. These details help us identify a suitable sensor configuration for your equipment.