How to connect optical sensor modules in series and parallel

Optical sensors can be connected in series for AND logic or in parallel for OR logic, but careful attention to voltage drops, current limits, and sensor type is essential.

Series Connection (AND Logic)

In a series connection, the sensors are wired so that the load is activated only when all sensors detect the target condition. This is commonly used for safety or redundancy purposes . Wiring Steps:

• For PNP sensors (sourcing type):
  1. Connect the positive terminal of the power supply to the positive input of the first sensor.
  2. Connect the output of the first sensor to the positive input of the second sensor, and so on.
  3. Connect the output of the last sensor to the positive terminal of the load.
  4. Connect all negative terminals (sensors, load, power supply) together.
• For NPN sensors (sinking type):
  1. Connect the negative terminal of the power supply to the negative input of the first sensor.
  2. Connect the output of the first sensor to the negative input of the second sensor, and so on.
  3. Connect the output of the last sensor to the negative terminal of the load.
  4. Connect all positive terminals together. Considerations:
• Ensure the total voltage drop across all sensors does not exceed the supply voltage minus the minimum operating voltage of the load .
• Series wiring effectively implements an AND function, meaning the load only activates when all sensors are triggered.

Parallel Connection (OR Logic)

In a parallel connection, the load is activated if any one of the sensors detects the target condition . Wiring Steps:

• Connect all sensor outputs to the load input.
• Connect all sensor power terminals to the corresponding supply terminals.
• For PNP sensors, the outputs are tied to the positive side of the load; for NPN sensors, outputs are tied to the negative side. Considerations:
• The sum of the leakage currents of all sensors must be less than the maximum OFF-state current of the load to prevent false triggering .
• Adding diodes to each sensor output can prevent interference and maintain individual sensor indicator functionality.
• Parallel wiring implements an OR function, meaning the load activates if any sensor is triggered.

Additional Tips

• Always check the sensor type (NPN vs PNP) and ensure the wiring matches the logic type.
• Use series resistors if needed to maintain minimum voltage across sensors.
• For multiple sensors in parallel, consider diode isolation to prevent backfeeding.
• Verify the maximum number of sensors allowed in series or parallel based on voltage drop and off-state current specifications . By following these guidelines, optical sensor modules can be safely and effectively connected in series or parallel for your application.