Sinking Sourcing I/O

“Sinking” and “Sourcing” terms are very important in connecting a PLC
correctly with external environment. These terms are applied only for DC
modules.
The most brief definition of these two concepts would be:
SINKING = Common GND line (-)
SOURCING = Common VCC line (+)

Most commonly used DC module options in PLCs are:
*Sinking input and
*Sourcing output module

  • Sinking I/O circuits on the I/O modules receive (sink) current from sourcing field devices. Sinking output modules used for interfacing with electronic equipment.
  • Sourcing I/O: Sourcing output modules used for interfacing with solenoids.

PLC AC I/O circuits accommodate either sinking or sourcing field devices. Solid-state DC I/O circuits require that they used in a specific sinking or sourcing circuit depending on the internal circuitry.

PLC contact (relay) output circuits AC or DC accommodate either sinking or sourcing field devices.