IO Device configuration - Startup Mode vs Priority

IO redundancy in Plant SCADA is achieved on IO device level. There are three Startup Modes

• Primary (in this mode, the IO device is always active for data acquisition once it is available)
• Standby (in this mode, the IO device connected but unused).
• Standby/Write (this mode is for the old style file based PLC, and not commonly used in green projects. If you want to use "Disk PLC", try to use the memory based IO devices with cached files)

As for priority, it needs to be used along with the startup mode. For a primary IO device, its priority number is the highest among redundant pair or a group of redundant IO devices. For example, you have 3 redundant IO devices, 1 primary (only one allowed) and 2 standbys. You assign priority numbers 1,2,3 respectively (smaller number, higher priority).  At runtime, if "P1" is offline, "P2" will be activated and start providing data if it is available, then followed by "P3".

For more information, please refer to online help Add an I/O Device | Topology (aveva.com)

The following IO topology is so called load balancing configuration for redundancy (regardless of protocol).

• Server 1 could be configured to host the primary IO device of PLC1 and the standby IO device of PLC2
• Server 2 could be configured to host the standby IO device of PLC1 and the primary IO device of PLC2

In the healthy condition, each server hosts data from only one PLC (the other one on standby). If one of these two server machines is offline for maintanace, the standby IO on the other machine will kick in and your SCADA system is still able to acquire data from both PLCs

Below is an example of using OPC UA protocol.

Hope this would help.

Regards,

Jacky

IO redundancy in Plant SCADA is achieved on IO device level. There are three Startup Modes

• Primary (in this mode, the IO device is always active for data acquisition once it is available)
• Standby (in this mode, the IO device connected but unused).
• Standby/Write (this mode is for the old style file based PLC, and not commonly used in green projects. If you want to use "Disk PLC", try to use the memory based IO devices with cached files)

As for priority, it needs to be used along with the startup mode. For a primary IO device, its priority number is the highest among redundant pair or a group of redundant IO devices. For example, you have 3 redundant IO devices, 1 primary (only one allowed) and 2 standbys. You assign priority numbers 1,2,3 respectively (smaller number, higher priority).  At runtime, if "P1" is offline, "P2" will be activated and start providing data if it is available, then followed by "P3".

For more information, please refer to online help Add an I/O Device | Topology (aveva.com)

The following IO topology is so called load balancing configuration for redundancy (regardless of protocol).

• Server 1 could be configured to host the primary IO device of PLC1 and the standby IO device of PLC2
• Server 2 could be configured to host the standby IO device of PLC1 and the primary IO device of PLC2

In the healthy condition, each server hosts data from only one PLC (the other one on standby). If one of these two server machines is offline for maintanace, the standby IO on the other machine will kick in and your SCADA system is still able to acquire data from both PLCs

Below is an example of using OPC UA protocol.

Hope this would help.

Regards,

Jacky

Hi Jacky, Thanks for confirming and the clarification.