Learn about interface outputs to OPC servers

When the interface writes a value to the OPC server, the interface waits for an acknowledgement (ACK) from the server, and monitors acknowledgements of writes.

To speed up processing of outputs, you can control output processing in the following ways:

• Configure multiple output groups

• Specify the number of outstanding writes a group is permitted

• Specify the amount of data to be sent in each write

To assign an output point to an output group, set its location4 attribute to the group number. For load balancing, output points with location4 set to 0 are distributed across output groups, including groups to which output points are explicitly assigned.

The OPC server is not required to accept more than one write at a time from any group, but many servers permit multiple writes to be sent without waiting for the first one to be acknowledged.

Even if the server accepts only one write at a time, defining multiple output groups can improve throughput. If you specify more outstanding writes than the OPC server can accept, PI Interface for OPC DA reduces its setting to the OPC server maximum.

You can specify how long to wait for the OPC server to acknowledge a write. If no acknowledgement is received in the specified period, the interface cancels the write and reissues it.

If your OPC server does not acknowledge writes, you can create an alert using the Device Status health point. Configure the alert to detect a desired number of queued writes. When the specified level is reached, the alert sets an alarm state and drops a specified number of values, oldest or newest.