A grain processing industry has a special system for transporting grains delivered by suppliers. This system is powered by a single electrical circuit made of three three-phase induction motors. These motors are responsible for the movement of the grains from the delivery point by the suppliers to the warehouse.

The operation is described below:

1. Each motor has a overload protection.

2. The system has a phase loss protection.

3. There is an emergency stop button in the command circuit.

4. The operation begins when the operator presses the power button located

in the command circuit.

5. The M1 motor drives a treadmill on which suppliers place the beans. The treadmill

takes the grains from the dropping point to the interior of the industrial property where it dumps them in a large motorized shovel that collects them. M1 only activates the treadmill when this shovel is fixed horizontally with the cavity facing upwards in the correct position to receive the grains.

6. The M2 motor drives the motorized shovel, rotating it 180 degrees in both directions. Therefore, if you have the shovel with the cavity facing upwards, it is receiving grains or at least until the deposit; if it has a cavity facing downwards, it will have thrown the beans into the deposit or will be captured to collect more grains. When it turns to collect grains, this movement is interrupted by a endstop swtich(ES), here called ES1. In this position, it stop for 5 min, the time controlled by a time relay, which commands the shovel to go to the warehouse. When a spin turns to pour the grains into the tank, this movement is stopped by a ES2 key, which controls the return of the shovel to collect more beans.

7. A weight sensor identifies the amount of grains(in kilograms) that is in the shovel when collecting the grains. If this value reaches or exceeds a safety threshold, the M2 motor is started regardless of the elapsed time. If this is the case, an M3 motor is started to assist in transportation.

8. In order not to overload the motors, M2 and M3 must change functions every hour, that is, M3 becomes the main motor and M2 the auxiliary one.

9. The start of the operation must take place with the shovel is ready to receive grains from the treadmill.

10. A yellow lamp should be activated if M2 or M3 are in operation, a green one if M1 is on and a red one if M2 and M3 are working together.

11. When the warehouse tank is full, a level sensor shuts down the entire system.

12. After any system shutdown, the operation is only restarted when the shovel is empty and correctly positioned to receive grains. This position is reached by a manual movement of the arm and the shovel.

Exercices:

#01 - Design a program in LADDER language to solve the same problem using PLC.

#02 - Test the system in a simulated environment using the ladder language program developed.

#03 - Diagram the power and the command circuit using real devices. Identify all the symbols used.