TOP Server Media-Level Redundancy Operating Modes

When using TOP Server Media-Level Redundancy, the Operating Mode specifies how the active device is chosen at runtime. There are 4 options:

Switch On Failure
Switch On Trigger
Primary Only
Secondary Only

Switch On Failure Mode determines that communication fails over to the selected secondary device when the primary device enters an error state. The system’s active device will return to the primary device once it is no longer in an error state. This Operating Mode allows the selection of an optional Monitored Item and Monitor Interval to monitor the health of the device connectivity. If the Monitored Item is left blank, a tag is automatically chosen.

The Switch On Trigger Mode is when the server monitors a configured trigger item. When the trigger condition becomes true, communication will switch over to the configured secondary device. If the condition is false, communication will remain on the primary device. The user will need to specify a Trigger Item, as well a Trigger Scan Rate (ms) and Trigger Type. The Trigger Type options are:

Quality Not Good – the failover occurs if the Trigger Item has any quality besides Good.
Value – the failover occurs when the Value of the Trigger Item is equal to, not equal to, greater than, or less than the specified value.
No Data Change – the failover occurs when the value of the Trigger Item does not change for a certain amount of time, specified in the Timeout (ms) property. This is helpful if your Trigger Item is a heartbeat tag that is expected to change its value at a certain interval.

Both Primary Only and Secondary Only are typically used for maintenance. Primary Only is selected when the Secondary is offline for maintenance and vice versa. Communication will not failover regardless of the error state