Basic PLC Ladder Programming Examples 19

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.

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