The FX1N input circuit can use either positive-going PNP signals or negative-going NPN signals. The SS terminal establishes the input common: connect SS to the supply polarity opposite the polarity switched into the X input.
Identify the required input logic
Choose one logic convention for the input group. With PNP sourcing logic, the field device applies the positive 24 VDC conductor to an X input. With NPN sinking logic, the field device applies the negative conductor to an X input.
| Input logic | Connect SS to | Signal applied to X input |
|---|---|---|
| PNP / sourcing | Negative supply conductor | Positive supply conductor |
| NPN / sinking | Positive supply conductor | Negative supply conductor |
Wire PNP sourcing inputs
For a PNP input arrangement, connect SS to the negative side of the 24 VDC supply. Wire the field sensor or switch so that it applies the positive side of that supply to the required input terminal, such as X0 or another X input.
Wire NPN sinking inputs
For an NPN input arrangement, connect SS to the positive side of the 24 VDC supply. Wire the field sensor or switch so that it completes the circuit by applying the negative supply conductor to the required X input.
Verify the circuit before operation
- Confirm whether the installed sensor switches a positive output for PNP or a negative output for NPN.
- Confirm that SS is connected to the opposite supply polarity: negative for PNP or positive for NPN.
- Confirm that the sensor and PLC input circuit use the same 24 VDC supply reference, whether the supply is internal or external.
- Activate the sensor or switch and verify that the intended X input changes state.
The available evidence does not include the referenced manual diagrams or exact FX1N terminal arrangement. Verify the physical terminal labels and the permitted use of the internal or external supply against the manual for the installed PLC before energizing the circuit.
FAQ
How do I connect a PNP sensor to an FX1N input?
Connect SS to the negative side of the 24 VDC supply, then connect the sensor so its positive switched signal reaches the required X input.
How do I connect an NPN sensor to an FX1N input?
Connect SS to the positive side of the 24 VDC supply, then connect the sensor so its negative switched signal reaches the required X input.
Can FX1N inputs use an internal or external 24 VDC supply?
The evidence identifies both internal and external 24 VDC supplies as possible sources. Confirm the exact terminals and supply-reference connections in the manual for the installed FX1N before wiring.