What Is The Difference Between Sink And Source Inputs/Output?

Sink and source refer to the direction of current flow between an I/O point on an I/O module and the connected device. It is only relevant for DC circuits with positive and negative polarities since current flows both directions in an AC circuit. It is important to select a sink or source I/O module based on the devices that you are going to connect. If the incorrect type module is selected, your circuit will not function properly. Sink (NPN) inputs and source (PNP) outputs are the most common in automation world.

Sink Input

For a sink input module, the current flow is from the connected device to the input.

Source Input

For a source input module, the current flow is from the input to the connected device.

Sink Output

For a sink output module, the current flow is from the connected device to the output.

Source Output

For a source output module, the current flow is from the output to the connected device.