Introduction to PLCs and Ladder Logic concepts. 

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+Reginald Alston II You are welcome. Thank you for the comment.

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+abdo boulanouar Thank you - glad you found it interesting.

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Industrial equipment often runs on 440 volts or higher and at many amps. Running wires for these gets expensive if you need to cover some distance and represents some level of hazard. It is more desirable to use low voltage, low current circuits for the control - particularly if there is come logic involved such as using limit switches or other sensors in a process. The relays let you separate the high voltage, high power circuits from the potentially complex control circuits.

to add to GeoffryThorpe123's response, (practically) all your modern computers and controls equipment run off of 24VDC, so they PHYSICALLY CANNOT send a signal strong enough to activate higher voltage circuits. For example, most motors you find in a factory run using 440/480 VAC (not DC), and require a current of several amps to turn on the motor ( called inrush current or Full Load Amps) because the electricity needs to physically turn the motor shaft. So instead of having a very expensive transformer ( to jump up voltage), Inverter (convert from DC to AC) and AMP (boost the signal strength) to get the signal of the controller compatible with the motor, you use an interposing relay. The relay takes a small 24VDC signal and physically closes a contact on the 480VAC circuit of the motor thus bypassing a ton of extra electrical equipment and adding the ability to physically separate 24VDC circuits ( safe to touch) and 120/480V circuits (hazard/deadly). and as Geoffrey said, not all equipment runs on a higher voltage circuit such as prox. switches ect, so adding high voltage equipment to the controller makes little sense. also, changes/updates to equipment and controllers are pretty common, so the more you separate differing voltage circuits the better. Example: if you had the transformer/inverter/amp ect. so you could just use switches and not relays like in your question, and then wanted to change the size of the motor. Now you have to change out all that expensive equipment to handle the new motor along with the motor itself. TIME + MONEY if you used relays all you have to change is the motor because everything from the controller to the relay would be the exact same. Plus changing motor stuff is fairly easy since industry uses MCC's ( Motor Control Center) which house all the high voltage motor stuff separate from the low voltage controls stuff.

Hsi S Relays can manage more current and isolate that circuit at the same time. ie. With a miniature switch you energize a relay that turns on/off a high(power=watts) lamp/bulb, or a powerful electric motor, using a relay. Relays are met to carry high amperage (current) without damage(burning) the switch.

I am not an expert but I will try to explain: you want separation between the running voltage of the motor and the low voltage of the controls. it's not safe to run 400V wires to where your controls might be. Also to start the motor you need a specialized contactor to deal with the arcing and inrush currents and so on.

if the switch holding the relay armature (which close the relay contact) is opened the system will either start or stop depending on which control switch is used. The switches handle low current and can be quite cheap,the relay contacts can handle high current ,high current switches are expensive and can burn out quite quick,whereas relays can be sealed and gas filled to avoid contact arcing and last much longer. Plus if the switches are just on and off,there is a risk of accidentally starting the device,because a toggle on/off switch can be knocked to the on position,whereas the feedback on/off system gives a bit more safety. So in short safety ,power handling and cost.

I find that Tim Wilborne ru-vid.com/show-UC_YccYdH0DBFp2ah0QuJ1lQ does a pretty good job.

Yea, pretty thin... Sorry. On the bright side, it's long gone.

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+rivendall Thank you for the comment. I'm glad this worked for you.

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+Jason Meyer Do I offer sympathy or congratulations? :-) Thanks for the comment.

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Some PLCs can be programmed in C (e.g. Siemens), many can not.

@@LightAndSportyGuy thank you sir for the reply.

Nope.

I had issues with the video quality and I need to re-record it when I get a chance.

+GeoffreyThorpe123 just upload them. u r good, i was looking how u start programming that device which u showed at start and which PLC software u use but .....plz upload fast.

Sorry that it wasn't fast, I have been out of the office. But it is now here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-GkuNgAK2sI8.html (I am moving the school related videos to a different channel and trying to clean things up a bit)

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Well, if you already know ladder programming then this video would have been 20 minutes of your life you will never get back - but my students typically have never seen any this and typically ask why can't we just program in C (which they know)... So I have to explain all this to them.

Sir, i would like you to understant that i am not against you and i really wish you the best. I did not watch the entire video, maybe that´s why ... And even if i had seen it all, it was not a waste of time, because i love to learn, and i don´t know everything so, it is always nice to watch other videos. I will watch now the entire video and give you my opinion later. I respect your way of teaching, and i hope you´ll get the recognition you deserve.

Mais vale voçe procurar outros videos que ensinem a programar ladder. Este não é o melhor, é muita conversa e pouca ação.

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