10 Practical Tips for Siemens S7-1200 Fault Diagnosis

Click on the blue text to follow us

[PLC Fault Diagnosis] How to Quickly Troubleshoot Common Faults of Siemens S7-1200? 10 Practical Tips to Make You an Expert in Fault Diagnosis!

The Siemens S7-1200 PLC is known for its stability and rich functionality, but even the best equipment can experience faults. This article shares 10 practical tips to help you quickly locate and resolve common issues with the S7-1200, improving your fault diagnosis efficiency. Whether you are a novice or an experienced user, these methods will help you remain calm when facing PLC faults.

1.

1. Start with the Indicator Lights

The LED indicator lights on the S7-1200 are the first step in fault diagnosis. Different flashing patterns represent different statuses:

• Green steady: Normal operation

• Red flashing: Hardware fault

• Yellow flashing: Program error

Note: Do not ignore the occasionally flashing yellow light, as it may indicate a potential problem.

2.

2. Check the Power Supply

Power supply issues are often overlooked, but they are one of the most common causes of faults.

• Use a multimeter to measure the voltage at the PLC power terminal

• Check if the power line connections are secure

• Pay attention to the heating of the power module

I once encountered an interesting case: a factory’s PLC kept rebooting around 3 PM. After investigation, it was found that this was due to the factory turning on high-power equipment at that time, causing voltage fluctuations. The solution was to install a voltage stabilizer.

3.

3. Communication Fault Diagnosis

Communication problems can prevent the PLC from interacting properly with other devices.

• Check the network cable connections and port indicator lights

• Verify the IP address and subnet mask settings

• Use the PING command to test network connectivity

Practical tip: Use the "Upload Site" feature in TIA Portal to quickly detect all Siemens devices on the network.

4.

4. Program Logic Check

Program errors can cause the PLC to malfunction.

• Use the online monitoring feature to observe program execution

• Check if the values of key variables are correct

• Be mindful of the use of loops and jump instructions

Common Trap: When comparing floating-point numbers, do not use the equal sign directly; instead, set an acceptable margin of error.

5.

5. Hardware Connection Check

Wiring errors or loose connections are also common causes of faults.

• Visually inspect the wiring for correctness and security

• Use a multimeter to measure input and output signals

• Check if the grounding connection is good

Once, while troubleshooting in a factory, I found the PLC input signals to be unstable. It was eventually discovered that the terminal block was contaminated with metal shavings; cleaning it resolved the issue. This reminds us that sometimes problems can arise from the most unexpected places.

6.

6. Use the Force Function

The force function of the S7-1200 can help us quickly locate problems.

• Force input signals and observe the PLC’s response

• Force output and check if the actuator operates normally

• Be careful to release the force promptly to avoid safety hazards

7.

7. Check System Logs

The system logs record important information about the PLC’s operation.

• View the diagnostic buffer in TIA Portal

• Analyze error codes and timestamps

• Pay attention to recurring error patterns

// Steps to view logs
1. Open TIA Portal
2. Connect to the PLC
3. Find "Online & Diagnostics" in the project tree
4. Select "Diagnostic buffer"

8.

8. Firmware Update

Sometimes, firmware bugs can lead to inexplicable problems.

• Check the current firmware version

• Look for the latest firmware on the Siemens official website

• Be cautious when updating to avoid compatibility issues

Warning: Always back up programs and configurations before updating firmware!

9.

9. Modular Fault Troubleshooting

For modular S7-1200 systems:

• Try unplugging and replugging the suspected module

• Replace with a module of the same model for comparison testing

• Check if the module configuration is correct

I once encountered a case where the PLC always reported a module error. After multiple replacements yielded no results, it was finally discovered that the oxidation of the backplane interface was the cause. After treating it with an electronic cleaner, the problem was resolved. This reminds us that sometimes the problem may not lie with the module itself.

10.

10. Use the Simulation Function

The simulation function in TIA Portal is a powerful fault diagnosis tool.

• Reproduce the problem scenario in a simulation environment

• Compare the differences between actual operation and simulation results

• Verify modification plans through simulation

// Simulation steps
1. Open the project in TIA Portal
2. Click "Start simulation"
3. Operate and monitor the PLC in the PLCSIM interface

11.

Practical Exercise Recommendations

1. Build a small control system that includes the S7-1200 PLC.

2. Deliberately introduce various faults, such as wiring errors, program bugs, etc.

3. Use the methods introduced in this article to troubleshoot and resolve these faults one by one.

4. Document the process and insights from each fault diagnosis.

5. Exchange experiences with other engineers and learn from each other.

Through repeated practice and accumulation of practical experience, you will surely enhance your PLC fault diagnosis skills quickly. Remember, the key to becoming an expert in fault diagnosis lies in systematic thinking and rich practical experience. Stay curious, keep learning new knowledge and skills, and you will go further in the field of PLC fault diagnosis.

Share

Collect

View

Like