Introduction to Siemens PLC Programming: Nine Classic Cases

Implement the bidirectional movement of the car using S7-200’s automatic control.

The control process is to press the start button, the car moves from left to right (and then back from right to left). When it reaches the right (or left), it hits the limit switch on that side, and the car automatically returns. Upon hitting the limit switch on the opposite side, it again returns. This back-and-forth movement continues until the stop button is pressed, at which point the car stops moving.

Download the written program to the Siemens S7-200 PLC for debugging, observe whether the results match the experimental requirements. Debug using the online control panel. When I0.0f (i.e., I0.0 is activated) is pressed, Q0.0 outputs, the light connected to Q0.0 will turn on, and at the same time, timer T37 starts timing. After one second, due to T37’s action, its normally closed contact opens, so Q0.0 has no output, and the connected light goes off. While the light is off, timer T38 starts, and after one second, the normally closed contact in series with timer T37 opens, so T37 resets, and its normally closed contact returns to normally closed. At this time, Q0.0 outputs again, and the connected light turns on.

Thus, the light connected to output Q0.0 turns on for one second and off for one second, flashing continuously until the I0.1f (i.e., I0.1 is activated) on the online control panel is pressed, at which point the flashing circuit stops working.

If you want to change the flashing frequency of the light, just change the timer’s time to achieve the desired effect.

Download the written program to the Siemens S7-200 PLC for debugging. After downloading, we will open the online control panel for debugging and check whether the results meet the requirements.

First, set i0.2f on the control panel to indicate that the button is pressed, i.e., i0.2 is activated, indicating that circuit breaker QF is closed. When the start button i0.0f (SB2) is pressed, i.e., i0.0 is activated, the motor starts in star mode, Q0.0 and Q0.1 output, indicating that both lights L1 and L2 are on, while driving the timer. When the timer counts to 10 seconds, it switches to delta start, at which point Q0.1 has no output, and Q0.2 outputs, so both Q0.0 and Q0.2 output, and the motor runs in delta mode. The lights L1 and L3 on the wiring panel are on. When the I0.1f on the online panel is pressed (i.e., I0.1 is activated), the motor stops running. All output points will have no output.

Download the written program to the PLC for debugging; after downloading, we will open the online control panel for debugging to see if the results meet the requirements.

After powering on the PLC, sm0.0 remains activated. Therefore, t37 starts timing. After the delay, t38 starts timing; once t38’s timer reaches 5 seconds, its normally closed contact opens, causing t37 to stop timing, and t37’s normally open contact returns to normally open, so t38 stops timing. At this point, t38’s normally closed contact returns to normally closed, causing t37 to start timing again, and counter C0 starts counting once. This repeats. When the count is 1, Q0.0 is activated. When the counter reaches 2, Q0.1 is activated, and so on.

When the counter reaches 8, Q0.7 is activated. When the counter reaches 9, the counter C0 resets. When I0.0f (i.e., I0.0) is activated, the counter and Q0.0~Q0.7 all reset, meaning no lights are on. When I0.1f (i.e., I0.1) is activated, the counter starts counting again, and the lights turn on one by one from Q0.0.

We set the light L1 to turn on when the value is 5. We set the light L2 to turn on when the value is 10. This way, we can see the experimental results faster.

When the online control panel button I0.0f is pressed (i.e., I0.0 is activated), it indicates that goods have entered. After clicking I0.0f on the online control panel five times, the counter value is 5 (indicating that there are 1000 boxes of goods in the warehouse), thus light L1 turns on, meaning Q0.0 outputs.

When I0.0f is clicked ten times, the counter value is 10 (indicating that there are 5000 boxes of goods), then light L2 also turns on, meaning Q0.1 outputs. When I0.0f is clicked continuously, the counter value continues to increase.

When I0.1f is pressed, the counter starts to decrease. Each click decreases the counter value by one. When the counter value is less than 10, it indicates that there are fewer than 5000 boxes of goods in the warehouse, and at this point, light L2 turns off (i.e., Q0.1 has no output). When I0.1f is clicked continuously and the counter value decreases to less than 5, it indicates that there are fewer than 1000 boxes of goods in the warehouse, and at this point, light L1 turns off, meaning Q0.0 has no output. When I0.2f is pressed, the counter resets. L1 and L2 turn off (i.e., Q0.0 and Q0.1 have no output).

Download the program to the Siemens S7-200 PLC for debugging. When the PLC is powered on, Q0.0 and Q0.2 will output, thus lighting up Q0.0 and Q0.2.

When the button I0.0f (indicating that I0.0 has input) on the online panel is pressed, timer T37 starts timing, and every 0.5 seconds, the color lights shift right using Q0.0 and Q0.2 as the base. When the button I0.1f (indicating that I0.1 has input) on the online control panel is pressed, the color lights shift left in the same manner.

➤Ladder Diagram Program

➤PLC Wiring Diagram

➤Ladder Diagram Program