When you look at an industrial control panel wiring diagram despite how many pages they include they most probably consist of two sections One is the Power or main circuit and the other is the Control circuit In this video we’re going to turn this control circuit into a PLC control circuit and draw the whole wiring diagram using EPLAN which is
an Electrical CAD software Then, you’ll learn how to convert this electrical wiring diagram into a PLC program The logic behind this electrical diagram is this conveyor system which is designed to move some pallets toward
a check weigher machine for that, it is equipped with a
three-phase electric motor Sometimes the operator must stop the conveyor and sometimes turns on the conveyor in the reverse direction to move the pallets backward Actually, this is a forward-reverse
motor control system or Clockwise and
Counter-Clockwise control system It is possible to implement this mechanism without a PLC but as you may know these days, even for small-size processes we use PLC systems to control all of the mechanisms in the process reduce the cabling works and have more control over the process now, it’s time to take a look at the old electrical diagram and turn it into a PLC-based wiring diagram There are lots of Electrical CAD software such as Automation Studio AutoCAD electrical EPLAN and so on but in this video I used EPLAN to draw the wiring diagrams Let’s draw the main or power circuit as this is the common circuit between the old and PLC wirings In this chapter, you’ll gain
some basic information about how to draw a
wiring diagram with EPLAN As you see on the left pane I’ve already created a new project First, I need a symbol for a
three-phase circuit breaker with thermal and short circuit protection Instead of drawing the symbol of this
specific standard device by myself I can access a quite complete
library of the symbols by easily clicking the “Insert” menu and then click on the “Symbol” submenu There are different libraries
according to different standards I open up the “IEC symbol” folder and then choose the
“Electrical engineering” subfolder I click over the “Protection device” and here I should search for a
three-phase disconnector switch and here it is! I choose it and tap OK After I insert the device I should adjust the parameters Other devices we need are two contactors one for Forward movement and
the other for reverse movement I just need the contacts
of a contactor here and will use their coils on
the control wiring diagram As you see when I want to place the
contactor under the circuit breaker the software automatically connects them I place them here and here I also need some terminals I need 4 of them and I place them one by one Now, I need a three-phase motor
symbol to add to our circuit I find it under
“power consumers” and place it as well The final action is to connect the mains power and the contactors So here I should choose
the “Interruption point” icon and insert three arrows corresponding
to the three phases of the mains power I name them L1 L2 and L3 There are some angled and Tee connections on the right-hand side toolbar
helping to connect the devices To connect the three-phase
power to the circuit breaker I need this one Ok, now we have power
on top of the switch To connect the reverse contactor I have to change the order of two phases and connect it to the output
connections of the forward contactor In this way, as we’ll
see later in this video the turning direction
of the three-phase motor will be changed As you see, I changed the order of the L1 and L3 I also have added a PE connection to the motor So, we’ve done with the power
section of the electrical drawing To save some time, I’ve drawn
the control circuits beforehand this is the OLD wiring diagram and
this is the PLC wiring diagram This Power circuit is applicable in
both systems without any changes So now let’s compare the two control
systems’ wiring diagrams step-by-step We have a video on “How to
read Electrical Wiring Diagrams” I suggest checking out that
if you haven’t already seen it as it helps you to get a better understanding
of industrial wiring diagrams Here when we push the Forward pushbutton the coil of the K1 which
is the Forward contactor will get energized and at the same time the K1’s normally open auxiliary contact will get closed to KEEP the circuit closed and maintain the power
to the contactor’s coil after we release the pushbutton The same thing will happen
to the Reverse contactor This time, as the order of the
two phases has been changed when the K2 contactor gets energized the rotation of the motor will be reversed To prevent the contactors from
functioning at the same time their NC auxiliary contacts
have been considered on the opposite circuit This is an NC contact from
the power circuit breaker which cuts the power
from the control circuit in case of overload or short circuit Therefore, to keep the motor safe the Run commands will be removed
from the motor immediately By pushing the Stop pushbutton as it has also a normally closed contact we can turn off the process manually So far, we saw that
everything was hardwired But in the PLC control systems things are a little bit different The PLC will replace and carry out the function of some of the hardware interlocks based on the software that we will write in the rest of the video Therefore, I’ve updated the control wiring as you see This page shows the PLC digital input card and the input signals that are wired to that This page shows the PLC output card and the signals that exit from that Let’s compare these two wiring diagrams on the same screen At the first glance the input devices are more or less the same The NO contacts that we have used for maintaining the power after releasing the Start pushbuttons are no more of use Instead, as we’ll see, the software will perform their function The software will also fulfill the function of these two contacts Here, we have the output devices like contactor coils that are connected to the PLC Digital output card and these are the signal lamps of the pushbutton Now, it's time to write the PLC software as always, I use the Siemens TIA Portal and if you want to learn more about that you can easily find the links to the
relevant videos in the description area as always, I first defined
the tags in the tag table The first four of them are inputs and the last two are the
outputs to the contactor coils As you learn in previous videos I should add an SR flip Flop for our electric motor I’ll add one for our Forward
movement to Network 1 I’ll add another one for reverse
movement to Network 2 I then add the Forward Pushbutton to the Set input of the Forward Flip Flop I also add the Stop Pushbutton to the Reset input of the Flip Flop As the Stop Pushbutton is a Normally Closed contact I had to add an NC contact for that You can watch this video to get a better
understanding of NO and NC contacts To stop the motor in case of faults I add the NC contact of the circuit breaker to the Stop input as well To save some time, I’ve done
the same things to Network 2 Now, I should add the software interlocks to replace the hardware we had omitted from the old wiring diagram If you remember, we had a retaining contact to keep the power on
the coil of the contactor after we release the start pushbutton The SR Flip Flop will do
the same thing for us and latches the Start command on the contactor Therefore, we don’t need to add anything to our software in these terms In case that the motor is running
in the Forward direction and the operator pushes
the reverse pushbutton the motor should not show any reaction In other words, the operator
should first stop the conveyor and then run it in the opposite direction To do that I have to add an NC contact of the Q0.1 to the start
input of the Flip Flop in series with the Forward Pushbutton and of course, I should add the NC contact of the Q0.0 to the start input of the Flip Flop in Network 2 Alright! Now, think about how and when to turn on the Start and Stop lamps of the pushbuttons and share the answer in the comments In a future video, you will learn how to wire the actual electrical devices of this process downloading this software to the PLC and simulate the process I really hope you’ve learned
something new from this video If so, please like and share this video with your friends,
colleagues or your students Thank you for watching
