While connecting field devices to Programmable
Logic Controllers we always get confused about sinking and sourcing operations.
Also this sinking & sourcing concept is useful to answer PLC interview questions.
Sinking and sourcing operations refer
to electrical configurations of the circuit in the module & field input
device provides current when it is ON it is said to be sourcing current.
device receives current when it is ON it is said to be sinking current.
are both sinking & sourcing field devices as well as sinking & sourcing
But it’s a common practice to use input
module in sinking current mode.
Field devices on the positive side (+VDC) of the field power supply
are sourcing field devices.
Field devices on the negative side (DC COM) of the field power supply
are sinking field
Sourcing field devices must be connected to sinking I/O cards and vice
Sinking field devices must be connected to sourcing I/O cards and vice