PLC program: Traffic signal light layout at the intersection

Traffic signal lights at intersections

1. Control requirements

(1) The signal light system is controlled by a start switch. When the start switch is turned on, the signal light system starts working. When the start switch is turned off, all signal lights go out.

(2) The north-south green light and the east-west green light cannot be on at the same time. If they are on at the same time, the signal light system should be turned off and the alarm should be sounded immediately.

(3) The north-south red light stays on for 25 seconds. At the same time as the north-south red light comes on, the east-west green light also comes on and stays on for 20 seconds. At 20 seconds, the east-west green light flashes, flashes for 3 seconds and then goes out. At this time, the east-west yellow light comes on and stays on for 2 seconds. At 2 seconds, the east-west yellow light goes out and the east-west red light comes on. At the same time, the north-south red light goes out and the north-south green light comes on.

(4) The east-west red light stays on for 30 seconds. The north-south green light stays on for 25 seconds, then flashes for 3 seconds before going out. At the same time, the north-south yellow light stays on for 2 seconds before going out. At this time, the north-south red light is on, and the east-west green light is on.

(5) The north-south and east-west traffic lights above alternate between working states in a repetitive manner, directing traffic at the intersection. The timing is shown below.

2. PLC Wiring

3. Define symbol address

4. Ladder Diagram Program

Three-story elevator control

The elevator's ascent and descent are controlled by an electric motor; the elevator ascends when it rotates forward and descends when it rotates reversely. Each floor is equipped with a call switch (SB1, SB2, SB3), a call indicator light (H1, H2, H3), and an in-position travel switch (ST1, ST2, ST3).

1. Control requirements:

(1) The call switches on each floor are push-button switches. SB1, SB2 and SB3 are all effective when turned on instantly.

(That is, it is still effective when it is connected and released instantly).

(2) The elevator body only responds to the rising call when it is rising, and only responds to the descending call when it is descending. Any call in the opposite direction is invalid, which is referred to as irreversible response. The specific action requirements are shown in the following table.

(3) The effective running time between floors should be less than 10 seconds, otherwise it will be considered as a fault and the motor will automatically stop.

PLC control of multiple liquid automatic mixing device As shown in the figure, there are three liquid mixing devices. SQ1, SQ2, SQ3 and SQ4 are liquid level sensors, which are connected when the liquid level is submerged. Liquids A, B, C and mixed liquid valves are controlled by solenoid valves YV1, YV2, YV3, YV4. M is a stirring motor. Its control requirements are as follows:

1. Initial state

When the device is put into operation, the valves of liquids A, B, and C are closed, and the mixed liquid valve is opened for 20 seconds to empty the container and then closed.

2. Start operation

Press the start button SB1, and the device starts to operate according to the following given rules:

①Liquid A valve opens, and liquid A flows into the container. When the liquid level reaches SQ3, SQ3 is turned on, closing the liquid A valve and opening the liquid B valve.

②When the liquid level reaches SQ2, close the liquid B valve and open the liquid C valve.

③When the liquid level reaches SQ1, close the liquid C valve and start stirring with the stirring motor.

④ After the stirring motor has been running for 1 minute, it stops stirring, the mixed liquid valve opens, and the mixed liquid begins to be released.

⑤ When the liquid level drops to SQ4, SQ4 changes from on to off. After another 20 seconds, the container is emptied, the mixed liquid valve is closed, and the next cycle begins.

3. Stop the operation

After pressing the stop button SB2, the operation will stop (stop at the initial state) after the current mixing operation is completed.

Reference Program:

Design of neon advertising screen controller

The specific requirements for using PLC to control neon advertising screens are as follows:

The order of the 8 tubes in the middle of the advertising screen is: the first tube lights up → the second tube lights up → the third tube lights up → ... → the eighth tube lights up, with a time interval of 1 second. After all are lit up, they are displayed for 10 seconds, and then they are turned off in the order of 8 → 7 → ... → 1. After all are turned off, they stop lighting for 2 seconds, and then the 8th tube lights up again, and the order of 7 → 6 → ... → 1 is lit, with a time interval of 1 second, and the display is displayed for 20 seconds, and then they are turned off in the order of → 2 → ... → 8. After all are turned off, they stop lighting for 2 seconds, and then start running from the beginning, repeating the cycle.

Reference ladder diagram program:

Design a program to make the two cylinders move sequentially in the order: A1B1B0A0.

(I) Air control circuit

(II) Displacement-Step Diagram

3. Analysis of Type I Obstacle Signals

(IV) PLC wiring

(V) Defining symbol addresses

(VI) Ladder diagram program

PLC Control of Vending Machines

As shown in the following figure, the working requirements of the vending machine are as follows:

1. This vending machine accepts 1 yuan, 5 yuan or 10 yuan coins.

2. When the total value of the coins inserted exceeds 12 yuan, the indicator light of the soda button will light up;

3. When the soda button light is on, press the soda button, and the soda will stop automatically after 7 seconds. During this time, the soda indicator light will flash. 4. When the coffee button light is on, press the coffee button, and the coffee will stop automatically after 7 seconds. During this time, the coffee indicator light will flash. 5. If the total value of the coins inserted exceeds the amount of money required by the button (12 yuan for soda and 15 yuan for coffee), the change indicator light will light, indicating the change action, and the excess money will be withdrawn.

Reference answer: