Basic PLC Ladder Programming Examples 18

Basic PLC Ladder Programming Training Examples for Beginners.  Hi friends, here we are starting unique a series of Free Training on PLC Ladder Programming & tutorials. These PLC Ladder Programs are important to learn basics of Ladder programs.

 PLC Ladder Practice Problem: 

Last-in Priority Circuit.
There are 4 buttons corresponding to 4 indicators. The program is to turn on the indicators corresponding to pressed buttons and to turn off the previous ON indicators.

   Topics Covered in this example is PLUSE instruction Ladder Program.

   Number of PLC Inputs Required

   X0 – Button 1. X0 will go from OFF to ON when pressed
   X1 – Button 2. X0 will go from OFF to ON when pressed
   X2 – Button 3. X0 will go from OFF to ON when pressed
   X3 – Button 4. X0 will go from OFF to ON when pressed

Number of PLC Outputs Required
Y0 – Indicator 1
Y1 – Indicator 2
Y2 – Indicator 3
Y3 – Indicator 4

PLC Ladder Programming:

Ladder Program Description:
·       When a button is pressed, the corresponding device X will go from OFF to ON. In this scan cycle, PLS instruction is executed, and the corresponding internal relay M is enabled as well. CMP instruction will be executed and the compared result is K1M0>0 which makes M10 ON but M11 OFF. [MOV K1M0 K1Y0] instruction will then be executed and sent out the state of M to its corresponding output Y. At the same time, the previous ON indicator(Y) will be turned off.
·       When it comes to the 2nd scan cycle, PLS instructions will not be executed and the value of M0~M3 will be 0. Therefore, the CMP instruction will be executed and set M11 to be ON (K1M0 = 0). [MOV K1M0 K1Y0] instruction will not be executed, and the 0 state of device M will not be sent out, either. In this case, Output Y will remain its original state until any other button is pressed next time.

Note: Example is only for training purposes. No practical implementation is done.

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