Have you ever heard of the terms “Sinking” and “Sourcing” in relation to PLC digital output modules? If you’ve been in the instrumentation and automation field for some time, you probably have. In this article, we will delve into the concepts of sinking and sourcing and clear up any misconceptions you may have.
Understanding Sinking and Sourcing
Sinking and sourcing are all about defining the direction of conventional current flow between two devices. Imagine current flowing from Device #1 to Device #2. In this case, Device #1 is sourcing the current, and Device #2 is sinking the current. Conversely, if the current were flowing from Device #2 to Device #1, Device #2 would be sourcing the current, and Device #1 would be sinking the current. In any situation where there is current flow between two devices, one device will be sourcing, and the other will be sinking.
Now that we have cleared up the basics, let’s explore how sinking and sourcing digital output modules work with real-world devices.
Sinking and Sourcing Digital Output Modules
PLC vendors manufacture both sinking and sourcing digital output modules. The difference between the two lies in the direction of conventional current flow. Let’s consider two devices with current flowing between them: a PLC output module and a relay.
In a sinking module, the current flows into the module from the load. On the other hand, in a sourcing module, the current flows out of the module and into the load. Essentially, one device is sourcing the current, while the other is sinking it.
Some vendors may refer to sinking and sourcing outputs as NPN and PNP outputs, respectively. An NPN module is a sinking module, while a PNP module is a sourcing module. These names originate from the types of transistors used in the output modules to complete the circuit. NPN modules utilize NPN transistors, while PNP modules use PNP transistors.
It’s worth noting that while an NPN module is always a sinking module, a sinking module may or may not be an NPN module. Manufacturers may employ other solid-state devices, such as MOSFETs, for switching in sinking modules.
To quickly identify whether a module is sinking or sourcing, you can examine the wiring diagram. If the wired-together load terminals connect to the plus terminal of the power supply, you have a sinking module. Conversely, if the load terminals connect to the negative terminal of the power supply or ground, you have a sourcing module.
FAQs
Q: What types of PLC digital output modules are there?
A: PLC digital output modules come in two types: solid state and relay.
Q: How can I identify if a module is sinking or sourcing?
A: One way to identify the type of module is by examining the wiring diagram. If the wired-together load terminals connect to the plus terminal of the power supply, it’s a sinking module. If they connect to the negative terminal of the power supply or ground, it’s a sourcing module.
Conclusion
Sinking and sourcing are essential concepts to understand when working with PLC digital output modules. By comprehending the direction of conventional current flow and identifying the type of module, you can ensure proper connectivity between your devices and optimize the operation of your PLC system.
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