How to set a fiber optic sensor to normally open and normally closed

You can switch a fiber optic sensor between normally open (NO) and normally closed (NC) modes using its configuration settings or teach-in function, depending on the sensor model.

Understanding NO and NC Modes

• Normally Open (NO): The sensor output is open (no current flows) when no object is detected and closes (current flows) when an object is detected .
• Normally Closed (NC): The sensor output is closed (current flows) when no object is detected and opens (no current flows) when an object is detected . The choice between NO and NC depends on your system requirements and how you want the sensor to interact with the control module.

Methods to Adjust NO/NC State

1. Using Sensor Buttons or Teach-In Function Many fiber optic sensors, such as the Wenglor OPT2041, allow you to toggle between NO and NC modes via a teach-in function or control panel buttons. This function also lets you adjust the sensing range to ensure accurate detection . Typically, you follow these steps:
   • Enter the teach-in mode using the designated button or input.
   • Select the desired output mode (NO or NC).
   • Confirm the setting and exit teach-in mode.
2. Using External Inputs or Configuration Software Some sensors, like the Keyence FS-V31, allow external input signals or software configuration to set the output mode. You can select NO or NC and adjust sensitivity or threshold values digitally .
3. Wiring Considerations (PNP vs NPN)
   • PNP (Sourcing) Output: Current flows from the sensor to the load. NO/NC mode determines whether the output is high (+24 V) or low (0 V) when the sensor is triggered .
   • NPN (Sinking) Output: Current flows from the load to the sensor. NO/NC mode determines whether the output is low (0 V) or high (+24 V) when the sensor is triggered . Ensure the sensor's output type matches your control system to avoid wiring conflicts.

Practical Tips

• Always check the sensor manual for the exact procedure, as the method can vary by model.
• Use the teach-in function to calibrate the sensing range before switching NO/NC modes to prevent false triggers.
• Verify the output with a multimeter or digital monitor to confirm the correct NO/NC behavior after configuration.
• For sensors with multiple outputs, some models allow simultaneous NO and NC outputs for flexibility . By following these steps, you can reliably configure a fiber optic sensor to operate in either normally open or normally closed mode, ensuring proper integration with your automation system.