Online Monitoring: How to trace logic in real-time.

1. What is Online Monitoring?

Online monitoring allows you to view the live status of your PLC program while it's running. You can see which inputs, outputs, and logic paths are active in real-time, helping you quickly identify issues and optimize performance.

2. Why is it Important?

• Real-time Troubleshooting: Quickly identify faulty signals or programming errors.
• Performance Analysis: Monitor scan times and system response.
• Maintenance Support: Diagnose intermittent faults without stopping the process.

3. Step-by-Step Guide

Here’s how to trace logic in real-time, using popular platforms like Siemens TIA Portal and Rockwell Studio 5000:

In Siemens TIA Portal:

1.Connect to PLC

• Open your project and go to Online → Go Online.
• Ensure your PC and PLC are on the same network.

2. Start Monitoring

• Open your program block (e.g., Main OB1).
• Click the Monitor icon (glasses symbol).
• Active rungs will turn green when conditions are TRUE and gray when FALSE.

Watch Variables

• Right-click variables → Add to Watch Table.
• Observe real-time changes in inputs, outputs, and memory bits.

Force I/O (if safe)

• Use Force to simulate specific conditions and observe program behavior.

In Rockwell Studio 5000:

1. Connect to PLC

• Open RSLinx and verify PLC communication.
• In Studio 5000, click Go Online.

2. Monitor Ladder Logic

• Open the program → Online Edit mode.
• Active coils and contacts will highlight in green (TRUE) or gray (FALSE).

3. Trend Tags

• Create a trend chart for critical tags.
• Analyze changing values over time.

4. Watch Windows

Use Watch or Quick Watch to monitor multiple tags simultaneously.

4. Pro Tips for Effective Monitoring

Use Cross-References to track signals across the program.

Enable Data Logging for intermittent faults.

Disable Forcing after testing to avoid unexpected behavior.