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Connecting Multiple PLCs to a Single HMI & Redundancy Options

Yes, Siemens HMIs can connect to multiple PLCs. Typically, you can connect up to 32 PLCs to a single HMI panel, depending on the HMI model and communication protocol used (e.g., S7 communication, OPC UA). Each PLC connection needs to be configured as a separate communication connection within the HMI project.

How it Works: You establish individual communication links to each PLC. Within the HMI project, you then tag data from each PLC, specifying which PLC each tag originates from. The HMI then reads and displays data from all connected PLCs based on these configured tags.

HMI Redundancy

Siemens HMIs do offer redundancy options, primarily through HMI Redundancy (High Availability System - HAS). This involves using two HMIs in a hot-standby configuration.

• Hot Standby: One HMI is active, serving the operator interface, while the other is in standby mode, mirroring the active HMI's configuration and data.
• Automatic Switchover: If the active HMI fails, the standby HMI automatically takes over, minimizing downtime.

More details on HMI redundancy can be found at: Siemens Support - HMI Redundancy

Workarounds (If Redundancy isn't Implemented)

If HMI redundancy isn't implemented, consider these points:

• PLC Redundancy: Implement redundancy at the PLC level to ensure continued operation if one PLC fails.
• Robust Communication: Utilize reliable communication protocols and network infrastructure.
• Error Handling: Design the HMI to gracefully handle communication failures with individual PLCs, displaying appropriate error messages.

Regards,
Siemens Self Support (Integrated with SiePortal)