Shadowing Practice: Sinking and Sourcing PLC Inputs Explained | What is the Difference? - Learn English Speaking with Video
Creating lesson...
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In this video, we're going to talk about syncing and sourcing PLC digital input modules and how they're connected to field devices.
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We will be using a Siemens digital input module with this part number.
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If you want to order this module online, you can head on over to the RealPars Marketplace or simply click on this link here.
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The two types of PLC input modules are digital and analog.
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A digital input module accepts inputs from digital devices such as switches and proximity sensors.
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The input module will detect one of the two possible conditions of an input device, open or closed.
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For example, a push -button switch is a digital device and can either be open or closed.
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We will examine how the input module detects the input device condition later in this video.
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The focus of our video is on digital input modules.
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Okay, let's go.
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As we said earlier, a digital input module will detect one of the two possible conditions of an input device, open or closed.
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So, the question is, how does the input module know if the input device is open or closed?
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All we need to do is construct a closed circuit containing the input device,
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the PLC input module, and a 24 volt DC power supply.
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If the switch is open, there is 0 volts at the module input terminal.
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If the switch is closed, there is a positive 24 volts at the module input terminal.
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The input module will detect either a no voltage or voltage condition at the input.
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These voltage conditions represent the open or closed conditions of the switch.
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These voltage or non -voltage conditions are represented by ones and zeros in the PLC memory.
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Every input device is connected the same way.
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If you have a 64 input module, it's possible to have 64 separate circuits.
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We'll show you more examples later.
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Alright, now that we know how the digital input module determines the input device condition,
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let's talk about the current flow between the power supply and the input module.
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There is a current flow, but it is very small and usually under 10 milliamps.
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Notice in our example that the current is flowing into the PLC module.
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Depending on the type of PLC input module and how it's connected with the input device, the current could flow in or out of the module.
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That's where the terms sinking and sourcing come into the picture.
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Let's spend some time clearing up any misconceptions you might have about these terms.
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When we talk about sinking and sourcing, it's all about defining the direction of conventional current flow between two devices.
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Think of it this way, current is flowing between device number 1 and device number 2.
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Ask yourself, which direction is the current flowing?
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The current is flowing from device number 1 to device number 2.
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Therefore, we say device number 1 is sourcing the current, and device number 2 is sinking the current.
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Okay, what if the current is flowing from device number two to device number one?
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In this case, we say device number two is sourcing the current, and device number one is sinking the current.
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In every situation where you have a current flow between two devices, one of the devices will be sourcing and the other will be sinking.
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PLC vendors manufacture both sinking and sourcing digital input modules.
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Let's explore what they are and how they differ.
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Remember what we discussed earlier, it's all about the direction of conventional current flow.
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Let's have a look at two devices with current flowing between them.
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One device is a PLC input module, and the second device is a push -button switch.
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Based on the connection polarity, the syncing module will have the current flowing into it from the switch.
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Ok, let's do that again, but this time our PLC input module will be a sourcing module.
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Based on the connection polarity, the sourcing module will have the current flowing out of it.
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Current can flow in either direction through a push -button switch because it is a passive device and not polarity -dependent.
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There are many active digital input devices used in industry today that are polarity -dependent.
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They must be wired correctly or they will not work at all.
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These active devices will be labeled as either syncing or sourcing.
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You can learn more about active sensors in our other videos.
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We'll direct you there at the end of this video.
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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 syncing.
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If the input device is a sourcing type, the PLC input module must be a syncing type.
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If the input device is a syncing type, the PLC input module must be a sourcing type.
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Adding confusion to already murky concepts,
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some vendors refer to syncing and sourcing input devices as NPN and PNP.
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You can learn more about NPN and PNP in our other videos.
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We'll direct you there at the end of this video.
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Here's something to remember.
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An NPN device is a syncing device.
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A PNP device is a sourcing device.
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The Siemens Digital Input Module 6ES7521 -1BH50 -0AA0 is a sourcing type.
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If you want to order this PLC module to use in your project, you can find the link in the video description.
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Let's connect a push -button switch and a syncing proximity sensor to two of the inputs.
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The current is flowing out of the PLC module because it is a sourcing type.
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Let's have a look at a syncing module.
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The Phoenix Contact Digital Input Module AXLSEDI16 -1 is a syncing type.
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You can find the link to order this PLC module in the video description as well.
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Let's connect a push -button switch and a sourcing proximity sensor to two of the inputs.
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The current is flowing into the PLC module because it is a syncing type.
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If you want to learn more, you might want to review two of our other videos called
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How to Wire Discrete DC Sensors to PLC Part 2 and What is a Transistor Working Principles.
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You can find the links to these videos in the description.
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Ok, let's review what we've covered in this video.
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A digital input module will detect one of the two possible conditions of an input device, open or closed.
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Digital input modules detect either a no voltage or voltage condition at the input.
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A sinking input module will have the current flowing into it.
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A sourcing input module will have the current flowing out of it.
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PLC vendors offer both syncing and sourcing digital input modules.
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An NPN device is a syncing device.
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A PNP device is a sourcing device.
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Want to learn PLC programming in an easy -to -understand format
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and take your career to the next level? head on over to realpars .com
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Vocabulary and speaking notes for this lesson
This speaking lesson is built on the video “Sinking and Sourcing PLC Inputs Explained”. The speaker keeps coming back to these words: input, device, module, current, sourcing. This video has 83 sentences and 1146 words to shadow. The speech runs for 8:30. The speaker talks at a steady 135 words per minute, a comfortable pace for shadowing. Only 74% of the words are among the 3,000 most common in English, so the vocabulary is demanding.
Key vocabulary in this video
15 words from the video worth learning, with pronunciation and meaning:
| Word | Pronunciation | Meaning |
|---|---|---|
| input noun | /ˈɪnpʊt/ | The act or process of putting in; infusion. |
| module noun | /ˈmɑd͡ʒul/ | A self-contained component of a system, often interchangeable, which has a well-defined interface to the other components. |
| sync noun | /sɪŋk/ | Harmony. |
| sink verb | /ˈsɪŋk/ | To descend or submerge (or to cause to do so) into a liquid or similar substance. |
| voltage noun | /ˈvəʊltɪd͡ʒ/ | The difference in electrostatic potential between two points in space, especially between live and neutral conductors or the earth. |
| detect verb | /dɪˈtɛkt/ | To discover or find by careful search, examination, or probing. |
| connect verb | /kəˈnɛkt/ | To join (to another object): to attach, or to be intended to attach or capable of attaching, to another object. |
| sensor noun | /ˈsɛn.sɚ/ | A device or organ that detects certain external stimuli and responds in a distinctive manner. |
| proximity noun | /pɹɒkˈsɪm.ɪ.ti/ | Closeness; the state of being near in space, time, or relationship. |
| vendor noun | /ˈvɛn.dɚ/ | A person or a company that vends or sells. |
| circuit noun | /ˈsɝ.kɪt/ | The act of moving or revolving around, or as in a circle or orbit; a revolution |
| terminal noun | /ˈtɚmɪnəl/ | A building in an airport where passengers transfer from ground transportation to the facilities that allow them to board airplanes. |
| dependent adjective | /dɪˈpɛndənt/ | Relying upon; depending upon. |
| conventional adjective | /kənˈvɛnʃənl̩/ | Pertaining to a convention, as in following generally accepted principles, methods and behaviour. |
| format noun | /ˈfɔːɹ.mæt/ | The layout of a publication or document. |
Phrasal verbs you will hear
| Word | Pronunciation | Meaning |
|---|---|---|
| clear up verb | /klɪəˈɹʌp/ | To clarify, to correct a misconception. |
Sentences worth repeating
Short, complete lines from the video that you can reuse in everyday conversation:
- We'll show you more examples later.
- Let's explore what they are and how they differ.
- Let's have a look at a syncing module.
Pronunciation to watch
The speaker uses 6 contractions and reduced forms, such as we'll, they're, we're. Say them the short way, as you hear them.
- The “sh” and “zh” sounds: conventional /kənˈvɛnʃənl̩/, confusion /kənˈfjuːʒən/, misconception /ˌmɪs.kənˈsɛp.ʃən/
- Long words — get the stress right: proximity /pɹɒkˈsɪm.ɪ.ti/, polarity /pəˈlæɹɪti/, misconception /ˌmɪs.kənˈsɛp.ʃən/
How to practise with this video
- Listen to the whole video once without speaking and note the words you do not know.
- Shadow it sentence by sentence at normal speed, repeating each one until your rhythm matches the speaker.
- Record yourself and compare with the original, paying attention to words like input, module, sync.
What is the Shadowing Technique?
Shadowing is a science-backed language learning technique originally developed for professional interpreter training and popularized by polyglot Dr. Alexander Arguelles. The method is simple but powerful: you listen to native English audio and immediately repeat it out loud — like a shadow following the speaker with just a 1–2 second delay. Unlike passive listening or grammar drills, shadowing forces your brain and mouth muscles to simultaneously process and reproduce real speech patterns. Research shows it significantly improves pronunciation accuracy, intonation, rhythm, connected speech, listening comprehension, and speaking fluency — making it one of the most effective methods for IELTS Speaking preparation and real-world English communication.