Sinking and Sourcing are two common terms used to describe the electrical connections between field devices (such as sensors, switches, and actuators) and programmable logic controllers (PLCs) in industrial automation. These terms refer to how the current flows in the external circuit when the device is activated by the PLC.

1. Sinking (NPN):

• In a sinking configuration, the load (e.g., an indicator lamp, solenoid valve, or relay coil) is connected to the positive voltage supply (Vcc), while the PLC's input or output module provides a path to ground (0V) when activated.
• When the PLC activates the output, it sinks current from the load, completing the circuit by providing a path to ground.
• Sinking inputs are often represented by "PNP" (positive-negative-positive) or "NPN" (negative-positive-negative) symbols in circuit diagrams.
• Commonly used with NPN-type sensors and devices.

2. Sourcing (PNP):

• In a sourcing configuration, the load is connected to the negative voltage supply (ground), while the PLC's input or output module provides a path to the positive voltage supply (Vcc) when activated.
• When the PLC activates the output, it sources current to the load, completing the circuit by providing a path to the positive voltage supply.
• Sourcing inputs are often represented by "NPN" (negative-positive-negative) or "PNP" (positive-negative-positive) symbols in circuit diagrams.
• Commonly used with PNP-type sensors and devices.

Comparison:

• Sinking (NPN):
  • Load connected to positive voltage supply (Vcc).
  • PLC provides path to ground (0V) when activated.
  • Current flows from positive to negative (load to ground) when activated.
  • Commonly used with NPN-type sensors/devices.
• Sourcing (PNP):
  • Load connected to negative voltage supply (ground).
  • PLC provides path to positive voltage supply (Vcc) when activated.
  • Current flows from positive to negative (Vcc to load) when activated.
  • Commonly used with PNP-type sensors/devices.

Choosing Between Sinking and Sourcing:

• The choice between sinking and sourcing depends on the type of field devices (sensors, switches, etc.) being used and the specifications of the PLC's input/output modules.
• Many PLCs support both sinking and sourcing configurations, allowing flexibility in system design and integration.
• It's essential to ensure compatibility between field devices and PLC inputs/outputs when configuring the electrical connections.

Understanding sinking and sourcing configurations is crucial for proper wiring and interfacing of field devices with PLCs in industrial automation systems. Incorrect wiring can lead to malfunctions, damage to equipment, and safety hazards.