Optimization Techniques and Best Practices in Siemens PLC Programming

Hello everyone! Today, let’s talk about the optimization techniques and best practices in Siemens PLC programming. Whether you’re new to PLCs or have written some programs before, I believe this article will inspire you. Optimizing PLC programs not only improves operational efficiency but also makes the programs easier to maintain, reducing debugging hassles later on. Next, we’ll explore how to write efficient and standardized Siemens PLC programs step by step!

1. Optimize Program Structure: Reasonable Division of Functional Modules

Why Divide Functional Modules?

In Siemens PLC programming, especially when using the S7-1200 or S7-1500 series, programs can often become complex. To make the code clearer, we need to divide the program into functional modules (for example: controlling motor start, handling counters, managing timers, etc.). It’s like renovating a house, separating different functional areas (living room, kitchen, bedroom) for better management and organization.

How to Achieve Modularization?

Siemens PLC supports Function Blocks (FB) and Organization Blocks (OB) to divide programs. We can create multiple function blocks and write different functionalities into the corresponding blocks.

Example Code: Create a Function Block for Motor Start

Here’s a simple FB example for controlling the start and stop of a motor:

FUNCTION_BLOCK FB_MotorControl
VAR_INPUT
    StartButton: BOOL;      // Start button
    StopButton: BOOL;       // Stop button
END_VAR
VAR_OUTPUT
    MotorStatus: BOOL;      // Motor status
END_VAR

BEGIN
    // Start logic
    IF StartButton THEN
        MotorStatus := TRUE;
    END_IF;

    // Stop logic
    IF StopButton THEN
        MotorStatus := FALSE;
    END_IF;
END_FUNCTION_BLOCK

Application Notes

• When calling this function block in the main program (OB1), you only need to pass the signals for the start and stop buttons.
• Tip: Writing frequently used functionalities as function blocks (FB) can improve code reusability and reduce maintenance costs for duplicate code.

2. Use Data Blocks (DB) for Efficient Data Management

Why Use Data Blocks?

In PLC programs, it’s often necessary to store and manage data, such as the current value of a counter, the status of sensors, etc. If this data is scattered all over the place, it can be very troublesome during debugging. Data Blocks (DB) provide a structured way to manage this data.

Data Block Application Scenarios

1. Global Data Storage: For example, saving the current status of the production line.
2. Function Block Parameter Storage: Each function block can be associated with an instance data block to store the inputs, outputs, and intermediate variables of that function block.

Example Code: Create a Global Data Block

Here’s an example of a global data block for storing sensor statuses and counter values:

DATA_BLOCK DB_GlobalData
VAR
    Sensor1Status: BOOL;    // Sensor 1 status
    Sensor2Status: BOOL;    // Sensor 2 status
    CounterValue: INT;      // Counter value
END_VAR

Application Notes

• In the program, you can access or modify data using DB_GlobalData.Sensor1Status.
• Note: Avoid frequently reading or writing variables in the data block, especially within the scan cycle, to prevent increasing the PLC’s load.

3. Optimize Scan Cycle: Reasonable Use of Timers and Counters

What is Scan Cycle?

The scan cycle of a PLC refers to the time it takes for the PLC to read input signals, execute the program, and update output signals. If the program is too complex or the logic is poorly written, the scan cycle can become longer, potentially leading to slower system response.

How to Optimize the Scan Cycle?

1. Reduce Unnecessary Logical Operations: For example, break complex conditional checks into multiple simpler steps.
2. Use Timers and Counters: Avoid performing time-consuming operations during every scan cycle.

Example Code: Using Timer to Control Flashing Light

Here’s an example using a timer (TON) to make a light flash every second:

VAR
    FlashTimer: TON;       // Timer instance
    FlashLight: BOOL;      // Flashing light status
END_VAR

BEGIN
    // Timer settings
    FlashTimer(IN := TRUE, PT := T#1S);

    // Invert light status when timer times out
    IF FlashTimer.Q THEN
        FlashLight := NOT FlashLight;
        FlashTimer(IN := FALSE);   // Reset timer
    END_IF;
END_FUNCTION

Application Notes

• Tip: The timer settings should be adjusted according to actual needs to avoid setting too short intervals, which can lead to frequent PLC operations.

4. Use Profinet Communication to Enhance Device Coordination Efficiency

What is Profinet?

Profinet is a commonly used industrial Ethernet communication protocol for Siemens PLCs, used for high-speed data transmission between PLCs and other devices (such as I/O modules, HMIs, sensors, etc.).

How to Configure Profinet?

In TIA Portal, you can configure Profinet through the following steps:

1. Add Profinet devices in the hardware configuration.
2. Set the device’s IP address and name.
3. Use communication function blocks (such as PUT and GET) in the program to implement data transmission.

Example Code: Using GET Function Block to Read Data

Here’s an example of using the GET function block to read data from a remote PLC:

VAR
    GetData: GET;                  // GET function block instance
    RemoteData: ARRAY[1..10] OF INT; // Array to store remote data
    Success: BOOL;                 // Communication success flag
END_VAR

BEGIN
    // Configure GET function block
    GetData(
        REQ := TRUE,
        ID := 1,                  // Communication ID
        ADDR := "192.168.1.2",    // Remote PLC address
        DATA := RemoteData,       // Array to store data
        DONE => Success           // Communication success flag
    );
END_FUNCTION

Application Notes

• In actual engineering, Profinet can be used to achieve multi-PLC collaboration or connect PLCs with upper-level systems.

5. Best Practices for Debugging and Maintenance

1. Use Online Monitoring Functionality: In TIA Portal, you can monitor variable values in real-time to quickly locate issues.
2. Keep Operation Logs: Save key data through HMI or data recording functions for later analysis.
3. Write Clear Comments: Each segment of code should have brief comments for easier understanding by yourself and others.

Conclusion

Today we learned some optimization techniques in Siemens PLC programming, including how to divide functional modules, use data blocks to manage data, optimize scan cycles, and configure Profinet communication. These methods not only make the programs more efficient but also make the code easier to maintain.

That’s all for today’s learning journey on Siemens PLC! Remember to practice coding, and feel free to ask questions in the comments. Wishing everyone a pleasant learning experience and continuous progress in Siemens PLC learning!