100 PLC Application Exercises For Electrical Engineers

PLC Applications

PLC Application Exercises includes most common applications in automation control, such as parking lot entry/exit control, material mixing, stock monitoring, level monitoring, traffic lights control, and conveyer belt control. This manual explains methods for applying basic instructions as well as advanced instructions of PLC to accomplish the field application purposes.

1. Entry/Exit Control of the Underground Car Park

Control Purpose:

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.

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.

Figure 1 – Application of Entry/Exit Control of the Underground Car Park

Devices:

Figure 2 – Control Program for Entry/Exit Control of the Underground Car Park

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.

2. Forward/Reverse Control for the Three-Phase Asynchronous Motor

Control Purpose:

Controlling the motor to run forward when Forward is pressed, run reverse when Reverse is pressed and stop when Stop is pressed

Figure 3 – Application of Forward/Reverse Control for the Three-Phase Asynchronous Motor

Devices:

Figure 4 – Control Program for Forward/Reverse Control for the Three-Phase Asynchronous Motor

Program Description:

X0 = ON when Forward is pressed. After 1 second, contactor Y0 will be enabled, and the motor begins to run forward. On the other hand, X1 = ON when Reverse is pressed. After 1 second, contactor Y1 will be enabled, and the motor begins to run reverse. Besides, Y0 and Y1 will be disabled and the motor will stop running when X2 is pressed.

The two timers in the program are used to avoid the interphase short-circuit when the motor changes its running mode. The short circuit may occur if another contactor is enabled instantly while the electric arc in the disabled contactor still exists.

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