Sinking and Sourcing Concept in PLC and their Difference

Sinking and Sourcing in PLC and their Difference

In this article we will learn about the sinking are sourcing concept and their difference in PLC wiring and their concept and can greatly affect the reliability and functionality of your control system.

Sinking in PLC Input Modules

The input card of a Sinking PLC input module is internally connected to the ground, so, the module receives current from a Sourcing field input device while it provides a ground connection for the external logic circuit.

Sourcing in PLC Input Modules

A Sourcing PLC input module has its input card wired internally to a positive voltage, so it sends out current from its control terminal to a Sinking field input device thereby providing a voltage source for the external logic circuit.

Sinking in PLC Output Modules

A Sinking PLC output module will have an electric current flowing into its control terminal from the connected load.

Sourcing in PLC Output Modules

A Sourcing PLC output module will have electric current flowing out of its control terminal into the connected load.

Difference between sinking and sourcing

Sinking	Sourcing
A sinking input circuit provides a path to ground for the sensor or switch connected to it.	A sourcing input or output provides the DC voltage to the load.
A sinking IO channel of a PLC requires a NPN transistor.	A sourcing IO channel of a PLC requires a PNP transistor.
A sinking input will have current flowing into it.	A sourcing input will have current flowing out of it.

Conclusion

Sinking and sourcing in PLC systems are essential concepts for managing current flow in digital input and output modules. By understanding the differences and knowing how to apply them, you can design more effective and reliable control systems. Whether dealing with buttons, sensors, or relays, this knowledge ensures your PLC setup operates seamlessly.

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