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Basic PLC Ladder Programming Examples 19

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: 

Entry/Exit Control of the Underground Car Park.

·       The entry/exit of the underground car park is a single lane passage which needs the traffic lights to control the cars. Red lights prohibit cars entering or leaving while green lights allow cars to enter or leave.
·       When a car enters the passage from the entry of the ground floor, the red lights both on the ground floor and the basement will be ON, and the green lights will be OFF. Any car entering or leaving is prohibited during the process till the car passes through the passage completely. When the passage is clear, the green lights will be ON again and allow other cars entering from the ground floor or the basement.
·       Similarly, when a car leaves the basement and enters the passage, any other car entering or leaving is prohibited till the car passes from the passage to the ground completely.
·       When PLC runs, the initial setting of traffic lights will be green lights ON and red lights OFF.


      Topics Covered in this example is SET RST instructions of Ladder Program.
    
      Number of PLC Inputs Required

    X1 -Photoelectric switch at the ground floor entry/exit. X1 will be ON when a car passes.
    X2 -Photoelectric switch at the basement entry/exit. X2 will be ON when a car passes.



Number of PLC Outputs Required
Y1 -Red lights at the entry/exit of the ground floor and the basement
Y2 -Green lights at the entry/exit of the ground floor and the basement

Number of PLC Internal Relays Required
M1- M1 will be ON for one scan cycle when a car from the ground floor passes X1.
M2 -M2 will be ON for one scan cycle when a car from the basement passes X1.
M3 -M3 will be ON for one scan cycle when a car from the basement passes X2.
M4 -M4 will be ON for one scan cycle when a car from the ground floor passes X2
M20- M20 = ON during the process of a car entering the passage from the ground floor.
M30 -M30 = ON during the process of a car entering the passage from the basement.

 PLC Ladder Programming:


Ladder Program Description:

·       The ground floor and the basement share the same red light signal Y1 and green light signal Y2.
·       The key of the program is to identify that the car is entering or leaving the passage at the ground floor entry/exit when M1 is ON to activate Y1 because [PLS M1] will be executed in both entering and leaving conditions. Therefore, the confirming signal M20 is required for confirming that the car is entering the passage from the ground floor.
·       Also, it needs to identify that the car is entering or leaving the passage at the basement entry/exit when M3 is ON because [PLS M3] will be executed in both entering and leaving conditions. Therefore, the confirming signal M30 is required for confirming that the car is entering the passage from the basement.

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

 See More PLC Ladder Programming Examples




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