One device is a PLC input module, and the second device is a push button switch. Based on the connection polarity, the Sinking module will have the current flowing into it from the switch. Based on the connection polarity, the sourcing module will have the current flowing out of it.
Current can flow in either direction through a push button switch because it is a passive device and not polarity-dependent. There are many active digital input devices used in industry today that are polarity-dependent. They must be wired correctly or they will not work at all. These active devices will be labeled as either Sinking or Sourcing.
If you recall, earlier we said that when there are two devices with current flowing between them, one device will be sourcing and one will be sinking. The current is flowing out of the PLC module because it is a Sourcing type. The current is flowing into the PLC module because it is a Sinking type. What is a Transistor Working Principles.
If you have any questions about the Sinking and sourcing PLC inputs or about PLC modules in general, add them in the comments below and we will get back to you in less than 24 hours. Got a friend, client, or colleague who could use some of this information? Please share this article. For example, the NI Datasheet contains the figure below.
The figure below shows that the current flows from the Vsup pin connected to the external power supply to the AO pin. Additionally, from the datasheet we can see that the current range of the NI is from 0 mA to 20 mA.
With these two pieces of information, we know that the NI can only source current, it cannot sink current from its Analog Out pins. This content is not available in your preferred language. Reported In. Reported In shows products that are verified to work for the solution described in this article. The light in this case is always attached to the power line, so when the switch is turned on, the neutral ground is connected sinked to the light, turning it on.
Sinking and Sourcing in Industrial Control Circuits. The kitchen light example simplifies the difference between sinking and sourcing circuits. PLCs work a little differently than your kitchen light or a simple control relay, however.
PLCs were developed to automate and simplify control relay circuits, eliminating much of the wiring and adding greater flexibility. PLCs can manipulate control systems programmatically rather than by hard wired control relays. PLCs use input cards to read the feedback of the control circuits.
Input cards connect internally to power or ground. An input card wired internally to ground is typically regarded as a sinking input card. If the input card connects internally to power, it is typically regarded as a sourcing card.
Think of the input card as the kitchen light, except in this case the light comes pre-wired to power or ground. Also See: Sink vs Source Animation. Sinking and Sourcing. For a sink logic, an NPN transistor provides a path to ground for the electrical load.
In other words, a sink logic circuit needs to be connected to a source logic circuit. Figure 1 shows a sinking digital output that is connected to a sourcing digital input. The input circuit is connected between the positive power supply side Vcc and NPN transistor.
For a source logic, a PNP transistor provides a path to voltage for the electrical load. In other words, a source logic circuit needs to be connected to a sink logic circuit.
This helps you visualize the current flow from the voltage source to load to the ground. A lot of my support was done remotely on the phone. That made wiring support very challenging. To be sure that I don't damage my customers' PLCs, I used to print the wiring diagrams out and then trace the current flow from the voltage source, to the electrical load, all the way to ground.
In order for a PLC sourcing output to trigger a sinking input on the driver, we need to make sure that everything has the power it needs. Sufficient voltage and current need to enter a positive terminal from the PLC side, through the output circuit, to the input circuit electric load , and then exit out from another terminal back to ground of the power supply to complete the circuit.
In order to save space, sometimes terminals are grouped together and thus called "common". This "common" could either be the voltage source, or ground. More info later. It's important to pay attention to the type of logic or transistor in order to determine the correct wiring method. In addition, there is also a difference with regard to safety. However, if the source logic was used, the input circuit is not directly connected to the positive power side Vcc , therefore earth leakage or short circuit of a signal line would not turn the input on.
That's why it's considered as one of the safer connection methods. Sink and Source are terms used to define the flow of direct current in an electric circuit.
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