You will prepare and submit a term paper on PLC Programming. Your paper should be a minimum of 1750 words in length.
An electrical ladder diagram consists of numerous electrical schematic symbols that are linked linearly to develop a diagram. An electrical ladder diagram has two basic portions. One portion is the power sections and the other portion is the control sections of the diagram. One line electrical ladder diagram is supplied with the machines by the manufacturers to troubleshoot the problems if the machine shows abnormal behavior of any kind (Rockwell Automation).In the above simple sample program, a normally open (NO) relay contact is used to turn on the lights or output coil.
The program shows that I: 1 is the input at terminal 1. I denoted the input. On the other hand, O: 0 is the output at output terminal 0. O is used for the output. Different PLCs manufacturers have different programming software. Different software use different indications for the input and output coils.In the above example, a different program is used for programming. In this program, physical input relays are termed as X0, X1, X2, and X3, where X0 and X2 are normally open (NO) relays’ contacts when PLC starts, and X1 and X3 are normally closed (NC) relays’ contacts.
In a similar manner, Y0, Y1 Y2, and Y3 are physical output coils, where Y2 and Y3 are normally closed output coils. When the PLC starts, the Y2 and Y3 coils remain ON. Here the words normally open refers to a relay that does not complete the circuit, when not energized. And NC relay is the relay that completes the circuit when it is not energized. In most of the PLC ladder logic programs either “,] [“or “| |” symbols are used for the input relays contacts, and “( )” is used to denote the output coil.
Different PLC ladder logic programs use different sets of instructions but in most of the programs, the ladder logic remains the same. The symbols for each of the functions are given at the menu bar, where the user can select the physical input relay contacts or other .functions according to the requirements. Let’s consider a program to run a motor through PLC with the help of push-button. .When the physical input at Xo is closed by applying 24 volts from the output of the PLC supply output to the physical input Xo through a push-button, the output coil gets energized.
It can be seen on the physical PLC device. The indicator LED light of the specific input and out blinks when it is energized.  .It is better to use the contacts of the output coil and connect it to another relay since it internal coil contacts of the PLC are unable to pass high current.