What is PLC Sinking and Sourcing? What is the difference between them? Sinking vs Sourcing in PLC

PLC (Programmable Logic Controllers)
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There are three popular types of output (Digital Output) cards.

1.Relay 2.Sourcing 3.Sinking.

Relay cards are very easy to interface but suffer from the mechanical limitation of low-speed operation and limited lifespan.

DC Sinking and Sourcing output card can switch output quickly and dont suffer from mechanical wear but exhibit some interface limitations.

Sourcing Output Card

Sourcing output cards are called P-N-P because the switching element was traditionally a P-N-P transistor.

PLC sourcing output module - Working

The PLC card connects V+ to the load.In sourcing output module during switch closure V+ is connected to the load and current flows as shown.

PLC sourcing output-Current flow

Advantages of Sourcing Output Card are - 1.Easier interface since only one power supply is required.

Disadvantage of PLC sourcing output card. 1.Voltage to the load is limited to the card supply voltage.

Sinking Output Card

Sinking output cards are called NPN because the switching element was traditionally a NPN transistor.

PLC sinking output module - working

These PLC cards connect ground to the load.

In sinking output module during the switch closure the load is connected to ground to the switch.The switch is hooked to ground and load is connected to the V+. Sinking PLC output module current flow

Advantages of PLC sinking output card. 1.Ability to switch voltages higher than card supply voltage.

Disadvantages of PLC sinking output module 1.Two power supplies are required for proper interfacing.

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Difference Between Sinking and Sourcing in PLC

Sinking vs Sourcing in PLC

Parameters Sinking Sourcing
Definition Devices that, when turned on, connect to the ground side of a circuit are referred to as sinking inputs/outputs, or I/O. When enabled, sources of inputs and outputs (I/O) supply current to the load.
Current Flow Direction Between the load to the input/output (I/O) device, current flows. The input/output (I/O) device sends current to the load.
Wiring Configuration The input/output (I/O) device is linked to the power supply’s negative terminal. The input/output (I/O) device is connected to the power supply’s positive terminal.
Typical Use Frequently utilised in DC circuits where grounding is necessary for the load to function. Frequently utilised in DC circuits where a positive voltage is needed for the load to function.
PLC Input Designation Current is sunk by the input device into the PLC input. Current is supplied to the PLC input via the input device.
PLC Output Designation Current is sucked from the PLC output by the output device. The PLC output is the source of current for the output device.
Common Devices Relays, switches, and sensors that need to be grounded. Voltage-supplying sensors, switches, & relays for a load.
Compatibility Requires matching input/output devices for sinking or sourcing. Requires matching input/output devices for sinking or sourcing.
Safety Considerations Reduced chance of unintentional short circuits because of grounding. Higher positive voltage means a higher chance of unintentional short circuits.
Circuit Symbol Usually represented with the symbol for ground. Usually represented by the sign for positive voltage.