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
devices.
When a
device provides current when it is ON it is said to be sourcing current.
When a
device receives current when it is ON it is said to be sinking current.
There
are both sinking & sourcing field devices as well as sinking & sourcing
input module.
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
devices.
· Sourcing field devices must be connected to sinking I/O cards and vice
versa.
· Sinking field devices must be connected to sourcing I/O cards and vice
versa.
