NPN, PNP and Two-Wire Sensor Output Reference
Compare sinking and sourcing sensor outputs, read simplified load-path diagrams, and check supply, input type, wire count, and exact product pinouts.
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Output function comparison
NPN and PNP describe common transistor output arrangements in DC sensors. Sourcing/sinking describes the current-path role of an output or input. Confirm whose terminal is being described: a sensor output and a PLC input can use opposite role names in the same connected circuit.
| Output | Active-state reference behavior | Load-path concept |
|---|---|---|
| PNP / sourcing output | Supplies the documented positive-side output path | The illustrated load returns toward the supply reference. |
| NPN / sinking output | Provides the documented low-side output path | The illustrated load is connected from the positive supply toward the output. |
| Push-pull / other output | A separately specified active output arrangement | Do not infer compatibility only from the words NPN or PNP. |
| NO / NC switching function | The output behavior relative to the defined sensing state | Not another spelling for NPN or PNP. |
Simplified current paths
Wire count and product pinout
| Description | Information to retrieve |
|---|---|
| Two-wire sensor | The specified series connection, operating range, load requirement, leakage and on-state drop. |
| Three-wire sensor | Supply, reference, and output functions from the exact diagram. |
| Four-wire or multi-function sensor | Whether the extra conductor is another output, complementary function, teach input, or another documented function. |
| Connector / cable colors | The exact pin-number view and cable/connector diagram; do not infer from the shell alone. |
The Schneider FAQ defines the output roles; OMRON’s guide distinguishes two-wire and three-wire connection conditions. Product wire colors and connector pinouts are not universal instructions for every industrial sensor.
Match the input
- Record sensor and input-module catalog numbers and supply requirements.
- Match output type and input current-path role using both manufacturer diagrams.
- Check reference/common arrangement, input thresholds, output current, voltage drop, leakage, and any isolation requirements.
- Confirm NO/NC behavior, response time, diagnostics, and commissioning requirements separately.
This reference does not select a PLC input module or approve safety-sensor use. Read the terminal reference for other device markings and keep observed configuration in the test record.