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OPC Troubleshooting

Resolving Data Communication Issues from the OPC Server

Updated over 3 weeks ago

OPC Introduction

An OPC server acts as a communication bridge between physical devices (such as PLCs) and client software (like SCADA, MES, or HMIs). It connects to industrial hardware using device-specific protocols (e.g., Modbus, Profibus) and then exposes this data using a standardized OPC interface. This abstraction allows client applications to access real-time machine data without needing to understand the native device protocol.

Troubleshooting Steps:

1. Verify Tag Updates

Check the last read time of relevant tags in the OPC server.

Ensure the tag values correlate with real-time machine data from the PLC or control system.

2. Validate PLC–OPC Connection

  • Confirm that the PLC is online and reachable from the OPC server machine.

  • Ensure correct IP address, port, rack/slot configuration, and that the PLC is in "Run" mode.

  • Restart the connection or rescan tags if needed.

3. Check Permissions and Security (especially for OPC UA)

  • Trust and install valid certificates on both the OPC server and the client.

  • Confirm that firewalls or antivirus software are not blocking required ports:

  • DCOM (OPC Classic): Often uses a wide range of dynamic ports.

  • Port 4840 (OPC UA): Ensure this port is open and not restricted.

  • Ensure appropriate read/write access is granted for the required OPC tags.

4. Review System Performance

  • Monitor the OPC server machine for high CPU or memory usage that could cause latency.

  • Check for network or I/O bottlenecks, especially when:

  • Polling a large number of tags.

  • Handling multiple OPC clients simultaneously.

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