What is sinking and sourcing in PLCs ?

Before going to discuss how to wired PLCs .We need to understand the concept of sinking and sourcing.

This is required to appropriately select the sensors, actuators, as well as the IO cards of the PLCs in the project.

Consider the circuit diagram shown here, we can see a power source and a switch and a lamp in series with it,

when the switch is closed, current flows through a circuit and lamp turns on.

As we can observe current first enters the switch, and then the lamp,

your switch is this sourcing type.

Now, let us modify this circuit, a bit. Let us first connect the lamp, to the power source, and then connect the switch in series in this circuit.

When we close the switch the lamp turns on. However, here, the current first enters the lab, and then the switch your, the switch acts as a sinking type, and the current sinks in the switch.

The same terminology is used to denote the sinking, or sourcing types of input or output modules of a PLC, or a controller.

If one has understood the circuit diagrams explained it would be clear that if a sensor is sourcing type, then the input module required would be a sinking type.

If the sensor is a sinking type, then the module would be a sourcing type. When the sensor gives a true condition. It acts as a closed switch. And in false condition. It acts as an open switch

in the figure shown the input module is a sinking type ,& the V positive, of all sensors will be connected to the positive point on the module and output of different sensors will be connected to the individual points on the input module.

When a sensor is triggered current first flows into the sensor, as shown in the figure, and then into the input module.

Hence, the input module acts as a sinking type. The same terminology can be used for a sourcing type input module.

When using a sourcing type input module. Care should be taken to connect the common of all the sensors to the ground terminal of the module.

Understanding this concept of sinking and sourcing will help us to select the sensors and actuators properly for the project, as well as the IO module of a PLC

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