How to Wire Discrete DC Sensors to PLC - Part 2

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How to Wire Discrete DC Sensors to PLC - Part 1:

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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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[caffeinatedinsanity]

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.

[mikeduman]

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

[eugenepohjola]

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.

[isaacadokwah]

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

[bobbyyoung]

Great Free advice and videos. Much appreciated.

[suheladesilva]

Great video, cleared a lot of my doubts, thanks.

[TheGoodSon]

Massive respect for sharing knowledge. Keep going!

[rodrigocardenassill]

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

[Dmntr]

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

[mernilodeleon]

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....

[lukaskohout]

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...

[mernilodeleon]

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

[suchayanmondal]

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.

[adriandeluna]

Perfect video congrats to your channel..

[juliuscontrolsandautomatio]

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

[eng.mohamedfandod]

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

[BW-xzol]

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

[dilantharuwan]

Nice explane and great work.keep it up

[sakirdag]

Tank you very much for very informative vedios

[michaelcostello]

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