How to Wire Discrete DC Sensors to PLC - Part 2

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✅ Check out the full blog post over at
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How to Wire Discrete DC Sensors to PLC - Part 1:
realpars.com/discrete-sensors...
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In this video, you will learn how to wire a 3-wire DC sensor, like an inductive proximity sensor, to a PLC input card.
You will also learn what a 3-Wire Discrete sensor is and recognize some of the common types of 3-Wire Discrete sensors.
DC sensors can be used to indicate the state of a device or a process to the PLC program.
Knowing these input states can allow the PLC program to make decisions, such as, when to start or stop a conveyor motor.
There are many types of discrete 3-wire DC sensors that can be wired to a PLC input.
Some 3-wire devices are NPN or “sinking” sensors, and some are PNP, or “sourcing” sensors. The difference is in how the device operates when the switch actuates.
NPN switches “sink” DC common to the black wire when the switch is activated.
PNP switches “source” 24 Volts DC to the black wire when the switch is activated.
Remember, in both cases, the black wire is connected to the PLC input channel terminal.
For most 3-wire devices, there is typically one brown wire, one blue wire, and one black wire.
A schematic of your specific DC digital PLC input card is required to determine how your specific device should be wired.
For a 3-wire PNP discrete input device, the brown wire will be connected to +24 Volts DC, the blue wire will be connected to DC common, and the black wire will be connected to the PLC digital input channel terminal.
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[@caffeinatedinsanity2324]

To those who might struggle with sinking vs sourcing input plc cards: Sinking means that the input needs to be connected to +24 V to cause it to be detected as "activated". Sourcing cards mean that you need to connect the inputs on the negative of the 24 V. And now for PNP vs NPN: PNP: when the sensor detects something, it's signal (or load. Black wire) gets connected to +24 V, so it "pushes" or "sources" 24 V. NPN: when detecting something, the signal wire gets connected to the negative, so it will "pull" or "sink" current. Same logic applies if you want to use 2 wire sensors in both types of cards.

[@enverismail6864]

So on the npn card you need -24 power supply. That must be connected to the bottom of the IO card (the very last slot) and the common must be connected to the very first slot; where the +24 would normally be supplied. It's the only way this is making sense to me

[@remingtonnathaniel6730]

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[@mikeduman358]

I have been an electrician for 20 yrs I understood the concept but the kiddies on the job always took the PLC wiring and us older guys did the heavy lifting, motors,conduit this helped me greatly thank you

[@suchayanmondal9858]

Very Informative videos. Thanks for providing us for the knowledge. Please produce more nice videos on several PLC related topics like this in future. Awaiting for the next.

[@isaacadokwah2739]

One of the best PLC videos ever. Very elaborate for easy understanding. Thanks for these great videos.

[@realpars]

What a great compliment, Isaac! Thanks a lot! We are always extremely happy to hear such positive feedback! If you ever have any questions, feel free to reach out to us. Happy learning!

[@rodrigocardenassill4700]

The best channel to learn, thank you for your valious content

[@realpars]

Thanks for your comment! Happy to hear that!

[@eugenepohjola258]

Howdy. Nice presentation. A couple of comments. 1. Using 2 -wire sensors (= Namur) the leaking current may be large enough to be detected as ON by the PLC DI card. To remedy this an external resistor of, say 10 k, may be connected over the input channel to deliver proper "sinking". 2. Separate 24 VDC power supplies should be used for input circuits and outout circuits. This prevents inductive load backspikes from generating "ghost" ON detections in input circuits. Alternatively the +24 rail may be splitted into two secondary + rails using two diodes in a back-flow blocking configuration. P600J is a 6 A diode. One secondary + rail powers the inputs and the other powers the outputs. The output secondary + rail should be fitted with a large electrolytic capacitor after the diode, say 2200 uF, between the + and the - to provide a place to go for possible backfire spikes. Electrolytic capacitors are not necessarily fast enough to kill spikes effectivery so a plastic capacitor of, say 1 uF, may be connected in parallel with the electrolytic capacitor. Regards.

[@realpars]

Thank you, Eugene! We appreciate your insightful comments!

[@TheGoodSon89]

Massive respect for sharing knowledge. Keep going!

[@realpars]

Much appreciated!

[@D0m1n4t0r33]

Thanks alot for your videos, they surely are helpful if you're setting up stuff for the first time!

[@realpars]

Great to hear that, Bas! Thanks for sharing.

[@mernilodeleon4081]

Yes sir...thanks a lot everyday i am watching your shared videos ...coz directly related to my work now...i wish i ciuld able to join your training....one of these day. Thanks and more power....

[@realpars]

Thank you Mernilo! Glad to hear that you're enjoying the videos.

[@marcbiss5953]

Very clear and informative! Thanks

[@realpars]

Great to hear that, thank you!

[@bobbyyoung2831]

Great Free advice and videos. Much appreciated.

[@realpars]

Glad you like them!

[@yem.t.3930]

Very comprehensive ! Thanks

[@realpars]

You're very welcome!

[@thairaltimemy7287]

Thanks a lot for your good ,brief , explanation....keep going

[@realpars]

You are very welcome, Thair! Happy learning.

[@darbarisid]

Very good explanation

[@zukhriddinmirzaumarov1758]

Thanks, really good job!

[@realpars]

Great to hear! You are very welcome.

[@eng.mohamedfandod1937]

excellent Go ahead i will support your channel in every where .

[@realpars]

Thanks a lot for your support, Mohamed!

[@spatikmedia]

Awesome..thank you Realpars

[@realpars]

You're very welcome!

[@sntgjmb6195]

Thanks for the information, from Ecuador

[@realpars]

You're very welcome! Happy to have viewers from all over the world! Happy learning ;).

[@javierferrer4634]

Very nice video!

[@ardentdfender4116]

Along with this very well explained video, can you please add a video for “loop Checking” or how to properly Loop Check of devices to Terminal Block or Input Card/ Output Card module for the RealPars video team to do.

[@realpars]

Thank you, Ardent! I have gone ahead and forwarded your topic suggestion to our creator team. Hopefully, they can add it to the list. Thanks again!

[@franciscojorge6568]

That's so cool plc exemple.

[@jimbass924]

Very informative, great graphics!!

[@realpars]

Much appreciated!

[@andyhandyman2118]

Always like and subscribed!

[@realpars]

Thank you, Andy!

[@mernilodeleon4081]

Great job...more technician like could benefits this learning....please continue...

[@realpars]

Thanks for watching Mernilo!

[@glaucioferreira13]

Thanks for this usefull video!

[@realpars]

You are welcome, Glaucio!

[@hayel2015]

You are the best to explain the PLC💝💝💝👍👍👍

[@mailalex27]

Tnx a lot guys. You’re the best

[@realpars]

You're very welcome, Alexander!

[@SinhPV]

Useful a video ! Thank for sharing...

[@realpars]

You're very welcome!

[@DannyJaves]

The best information excellent

[@WangsaGiri]

Hello.. Thankyou for your clear explanation about this. I am just learning about this PLC thing. but i have more question. how do you connect multiple let say 4 Proximity sensor. Thanks again

[@MrPromerican]

Thank you real pars

[@realpars]

You are very welcome!

[@GRant16NCH]

Thanks for video

[@sakirdag2976]

Tank you very much for very informative vedios

[@realpars]

Thank you! We are always extremely happy to hear such positive feedback! If you ever have any questions, feel free to reach out to us. Happy learning!

[@suhail8086123757]

Wonderful videos

[@suhelpatel2028]

Beautiful 👌

[@KevinNguyen-tw5ml]

Thank you very much !

[@realpars]

You are welcome!

[@Rexbo12]

Really well explained. Thank you

[@realpars]

Glad you liked it!

[@Rexbo12]

I'm just starting to learn about plc as its going to be needed for my new position thanks a lot even dumb ass like me can understand

[@jcerranom]

Simply Awesome!!

[@realpars]

Glad you like it, Julio!

[@mprv3755]

Great video. Possibly a video on how to use “scale/ scaling ” PID instruction on Analog instrumentation on Siemens or Allen Bradley?

[@realpars]

This topic is covered in a 9-part course on using the PID instruction in an S7-1500 on the Realpars.com learning site. Come subscribe and give it a try!

[@xhuljan11]

Thanks a lot ❤️

[@boothhits6144]

great channel thank you so much

[@realpars]

Thanks for your support!

[@shuhaibvk2456]

Very informative👌🏼

[@realpars]

Happy to hear that! Thank you, Shuhaib!

[@dilantharuwan7373]

Nice explane and great work.keep it up

[@realpars]

Glad you liked it, Dilantha!

[@adriandeluna8906]

Perfect video congrats to your channel..

[@realpars]

Thank you very much, Adrian!

[@user-ro6ou5vb8y]

Thanks God for sharing this matter i indeed very interested and i wish i could learn more about plc such as how to program.

[@realpars]

You are welcome!

[@kittylayyon2789]

Thanks real pars

[@realpars]

You are very welcome!

[@juliuscontrolsandautomatio6861]

So great! So good! 👏👏👏👏 I'd like to learn about how to Wire Discrete DC Sensors to Variable Frequency Drive.

[@realpars]

Great suggestion! Thanks for sharing and happy learning, Julius!

[@grow8151]

Very good

[@andersonsardinha1504]

Perfect 😃

[@michaelcostello6991]

well explained with appropriate diagrams. Only guys like you should have a license to teach !!!

[@realpars]

That's a great compliment, Michael! Thanks a lot!

[@amilabalasooriya8944]

Thanks.keep going

[@realpars]

Thanks for watching!

[@eliosgreek8028]

Great video

[@realpars]

Thank you, Elios!

[@hiwaabdulrazaq7920]

Thanks

[@alhassanalmusawy2056]

thanks,and please keep going

[@realpars]

You are very welcome! Thanks for your support!

[@charliechimples]

Great vid once again, well explained. 🐵

[@realpars]

Thanks a lot!

[@mikemwabilwa572]

Many thanks

[@realpars]

You are very welcome, Mike!

[@ahmedadebakin8189]

Really nice video but I have one question concerning NPN sensors. If I give positive to the brown wire from the PLC will I still connect same to common of the Input card?

[@keerthi47kv]

Please keep going

[@night_grinder1378]

Greatvideo. Real pars. Can you make video how to troubleshoot devices.? Thanks it will help a lot.

[@realpars]

Thanks for your support, Christian! And thanks for the topic suggestion, I will definitely go ahead and forward this to our creator team. Happy learning!

[@davidmejia9011]

Awesome

[@lukaskohout419]

8:00 i think there is error in diagram--- if we talk about Voltage which is difference in potential between two poles then if you are showing +24VDC as positive pole and -24VDC as negative pole then you have potential of 48V! So it should be +24V and 0V or +12V and -12V etc...

[@realpars]

The blue wire is common, or the negative side of the 24VDC power supply. The voltage difference between +24VDC and what is shown as -24VDC (common) is 24VDC. To be clearer, the common connection should have been shown as 0 VDC. Thank you for the observation and comment.

[@samisrour3129]

great videos.. hope to be fine

[@priceless55]

Simplicity is the key. :)

[@realpars]

Definitely! ;)

[@maruthiprasad8184]

Team,Thank you so much for valuable information. I have a doubt on control valve resolution concept from long time. Is it possible to make a video on this concept. It will be great help to everybody.

[@realpars]

Hi Maruthi! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

[@GRant16NCH]

Make vedio.. different connection AI, AO analog detection

[@industrialautomationknowle373]

I like it

[@BW-xz6ol]

14:30 if connecting to plc input 3 shouldn’t black wire Goto B? I think you meant to say if it connects to plc input 2 then it goes to terminal A. I’m new to all this... so thank you very much for all your videos

[@nileshpatil5644]

Awsome.....

[@realpars]

Thanks!

[@3498137]

Excellent¡

[@realpars]

Thank you!

[@runbou3485]

Thankអរគុណ👏

[@syedjawadable]

please make videos on encoders and resolver .

[@toddmaggio2032]

Thank you for your educational videos. I have a two question that you might have already answered elsewhere. If so I'd be grateful for the links. Can a proximity sensor be used as a SPDT switch? Say I want a conveyor belt go back and fort. Can the wiring be tweaked in such way that sensor reverses the direction of the electrical circuit and make the conveyor belt reverse its direction?

[@realpars]

A proximity sensor be used as a SPDT switch only if it is designed as a SPDT switch. Many (if not most) proximity switches used today are solid state, so there is only one output available, and it is transistor output, not a Form C contact. For your second question, you can use the proximity switch input as a trigger for PLC logic to act to reverse the belt. You likely will also need some timers in this logic as well. If you were to do this in a hardwired system, it can be done with a series of relays, sensors, and timers, but the proximity sensors would still be wired as shown in this video.

[@younismustafa5763]

Great

[@realpars]

Thank you!

[@wasuts.444]

Your videos very helpful, Thanks very much. and I saw the subtitles start at 15:35 explain about PNP but your are talking about NPN first, I think the subtitles was wrong place, just let you know.

[@realpars]

You're right! Thank you for letting us know.

[@wasuts.444]

RealPars You’re welcome.

[@eliehajj3777]

A "Sinking" PLC input card has (0 VDC) commonly connected to all its Inputs. Therefore it needs PNP Sensors to be connected to it. A "Sourcing" PLC input card has (+24 VDC) commonly connected to all its inputs. Therefore it needs NPN Sensors to be connected to it. So for the example in the video above the inputs (from I0.0 to I1.7 ) should be commonly connected to ( - ), therefore terminals 10 and 11 should be connected to ( - ), not to (+24 VDC) because it is a "Sinking" input card and only accept PNP sensors. I hope that I'm wrong.😀

[@bitebonumbere1426]

Awesome videos. Please can you upload the subtitles? The auto-generated one is difficult to follow. Thanks.

[@realpars]

Hi Bitebo, Thanks for your comment! We have English subtitles for almost all our KZbin video courses. Unfortunately, some of our older video courses do not have this, and only have the auto-generated option. Sorry about that, hopefully you are still able to enjoy them!

[@bitebonumbere1426]

@@realpars meaning is it impossible to add subtitles?

[@longhungtruong7980]

I have one question for RealPars: What exact function difference between 2-wire and 3-wire DC sensor? Use the 2-wire one is more easier than 3 wire when we connect with PLC. So, Why we don't have 2-wire DC sensor for Level switch and pressure switch? The information of this video is excellence. Please help me answer previous question. Thank RealPars.

[@realpars]

The difference is fairly simple to explain. Sensors that are simple contact closures, such as limit switches, flow switches, hall-effect proximity switches, and vibratory level switches are all two-wire devices. One wire is 24VDC+ and the other is common, or 0VDC. These sensors are either mechanically or magnetically actuated or can use the 24VDC+ wire to power the device. Sensors based on solid-state technology require 3 wires. Solid-state devices are based on transitor circuits which require 3 wires: 24VDC+ applied to the base, a signal wire that goes back to the PLC as the input from the collector, and a ground wire for the emitter. Solid state devices are smaller and many times configurable as to setpoint, trip point, etc., but they also require 3 wire connections. That is why it is important to understand how to properly connect these to the PLC.

[@longhungtruong7980]

@@realpars So, Thanks for your explanation. I'm clear about function of both sensors types. Please release more videos like this. I keep following and learning with you.

[@tomcasarella6061]

A PNP device is wired to a PNP card the common on the card is Negative input to the card is Positive

[@yosefali7729]

is it safe to power the Sensors and field devices through the PLC input card, most cards have really low limit on current so connecting like 10 - 12 devices might be risky, how about powering it through a Power supply instead from the PLC input card ? wouldn't that be better ? appreciate your efforts in simplifying this great effort

[@realpars]

Thank you for your question. In our videos, we focus on sensors specifically designed to interface with a PLC. The input cards are responsible for receiving signals from these sensors, while the output cards supply power to your device according to your engineering specifications and current requirements. If necessary, the output cards can also power relays for handling larger currents. Every industrial PLC manufacturer typically provides a manual detailing how to use and program their PLCs. Additionally, it's important to ensure you have a suitable power supply to energize your system. Happy learning!

[@davidpalmer963]

Image result for what can a inductive proximity switch detect? Inductive proximity sensors can only detect metal targets. They do not detect non-metal targets such as plastic, wood, paper, and ceramic

[@frankietrenado9327]

I believe if wiring into IO channel 0.3 the black input wire should go to terminal D

[@realpars]

It does. In video, terminal 1 is 24VDC, terminal 2 is I0.0, terminal 3 is I0.1, terminal 4 is I0.2, and terminal 5 is I0.3, connected to "D".

[@isidrovaldez2391]

I don’t think that an inductive proximity switch could detect a box. I was under the impression that an inductive prox only detected ferrous metals, and a capacitive proximity switch would be used to detect things like plastics, wood, liquids, and boxes.

[@aprilc6312]

What if the box is metal?

[@mnada72]

Sinking switch (NPN) needs sourcing module hence the common of the module is positive Sourcing switch (PNP) needs sinking module hence the common of the module is negative

[@imamulkabirhimel7477]

What if i want to connect npn switch. Should the brown be connected to 20 and blue to 10?

[@pradippatole1328]

plz share video related to potential free contact and wetted contact

[@realpars]

Glad to have you as a subscriber! :)

[@Logical_Controls]

Informative video. Thanks. FYI slight text error @ 7:53

[@realpars]

Thank you! Happy to hear! I just double checked to video. However, I couldn't spot any error.

[@Logical_Controls]

Thanks for the reply Realpars. Nothing major, it's just says +24VCD instead of +24VDC. Also shouldn't it be 0VDC for the blue wire as opposed to -24VDC which is a negative voltage instead of a ground?

[@chuchuokeke]

Also, plc terminal 2 is point A on the marshaling terminal block..i think you said point 3 is A..great work, very informative. Keep it up for more likes!

[@ikramantaki]

I WANT THE COURSES¡¡¡ WITH YOUR HELP I´LL GET A JOB

[@realpars]

Happy to hear your motivation! Have you looked at our course library yet? realpars.vhx.tv/browse

[@ikramantaki]

RealPars yes, I already subscribed

[@adhavtejashri]

How we can connect 2 proximity switches at 24 vdc common terminals.

[@realpars]

In the video, only one sensor is connected. If you have multiple sensors connected to the PLC card, external terminal blocks will be required. If you have a 16-point input card, there will ultimately be 16 connections to 24 COM. In this case, I would take 17 DIN-rail terminal blocks, jumper them together, connect the input common wires to the first 16 terminal blocks (one per block), and connect the 17th terminal block to 24 COM.

[@jawadkhan6531]

Connect two wire riela

[@psi23k]

@8:23 you show the brown wire from the npn sensor connected to the negative of the I/O card. Is that correct? Shouldn't it be connected to 10 or 11?

[@realpars]

For a sinking sensor, the brown wire is connected to the most positive terminal on the PLC card. In this configuration, 24VDC is applied to the common terminal of the PLC card, as shown. This is true for the Siemens DI card chosen, but it is always good to check the specific wiring diagram for the card you are using before connecting a sensor. Some manufacturers have different models of DI card depending on the sensor type (sinking or sourcing).

[@tipko1863]

Am I missing something or is the wiring diagram for the PNP type switch around 9:09 (where - is the common wire on the input cards) different than than the one shown around 13:57 where the +24V is the common for the 2 groups of inputs?

[@realpars]

No. in both cases, the (-) is attached to terminal 20 on the I/O card, which is common (blue wire).

[@tipko1863]

@@realpars Alright, so then the wires connecting pins 10 and 11 to 24 V are used to power those groups of inputs or something else?

[@photog1529]

New to this, but a question. at about 14:34, you state if the proximity switch is connected to terminal 3, the load wire would be connected to "A"...shouldn't the load be connected to "B"?

[@realpars]

At that point in the video, the schematic correctly shows a PNP sensor connected to the first channel of the PLC card, which is at terminal 2 of the input card, or terminal A on the marshalingpanel. The narration says "PLC input channel 3", the black wire should be connected to C, which is connected to screw terminal 4 on the PLC card.

[@abrahamgreenidge8924]

Hello, do you have any basic basic basic instructional video on the wiring of PLC? I’m neww to this & has 0 experience.

[@realpars]

This video and the companion Part 1 video provides good instruction on wiring discrete devices to the PLC. Other RealPars videos give instruction wiring other modules, power supplies, etc.

[@rahibqurbanov3116]

👍👏

[@jay_rana]

What will be the connection for npn switch?

[@realpars]

Watch this kzbin.info/www/bejne/aKHHp6mnoMyod5Y

[@sattara6901]

RealPars this link dosn't work

[@realpars]

Hey! I just checked the link kzbin.info/www/bejne/aKHHp6mnoMyod5Y and it works fine. Can you please try again? :)

[@scottsommer6480]

In the video linked at kzbin.info/www/bejne/aKHHp6mnoMyod5Y, start watching at about 6:30 for the discussion of wiring of an NPN device.

[@bobbyyoung2831]

Concerning the PNP prox. switch wiring portion...I'm confused about the following statement, "If we connect the proximity switch to PLC input channel 3 then the black wire will land on terminal A." 2 thru 9 are inputs. video shows A being 2 dose it not? I am a beginner at PLC's so please explain where I am going wrong. Thanks

[@realpars]

You are correct, to wire to channel 3, the black wire would land on marshalling terminal "C".

[@P.J16]

7:49 Blue wire should be -24 Vdc or just O V?

[@realpars]

It is best to consider the blue wire as common, or 0V.

[@phillyo51]

How can you find out which cards are compatible with PNP or NPN?? I've checked the siemens support website but have found no information. Cheers.

[@realpars]

Check out this article: support.industry.siemens.com/cs/document/23451499/what-is-the-meaning-of-the-terms-sinking-(german%3A-p-lesend-)-and-sourcing-(german%3A-m-lesend-)-in-digital-modules-of-simatic-?dti=0&lc=en-WW The cards compatible with NPN and PNP wiring are listed toward the bottom of the article referenced above.

[@venkatvijayakumar6176]

Hi, I have two Level Sensors which is 4-20mA type. But, I have only one 24 VDC supply adapter. Is it possible share the DC supply to two sensors to get the 4-20mA output?

[@realpars]

Yes, as long as your power supply can output at least 50ma (20ma for each sensor). This is normally how analog circuits are set up: common power supply with individual milliamp signals back to an analog input card. The sensor is the device that regulates the milliamp signal.

[@venkatvijayakumar6176]

@@realpars Thanks a lot, I'll check on that.

[@MegaRyad]

if you put electrons going in and out in the animation it would have been better to understand this pnp and npn sensors , thank you

[@realpars]

Thanks for the feedback! I will happily go ahead and pass this on to our course creators. Thanks again for sharing and happy learning

[@richatpurba9047]

so if we accidentally buy a PNP switch when it should be an NPN switch, we can't just switch the wiring termination to make it works?

[@realpars]

This can be done only if the PLC card supports sourcing and sinking type switches. An NPN sensor requires a sourcing PLC input and a PNP sensor requires a sinking PLC input.