KEPServer Data Scan Time|Classic OPC: DA, A&E, HDA, XML-DA, etc.|Forum|OPC Foundation

There are several factors involved.

1. The client can set the update rate to the as fast as 10 msec but that does not mean that the driver will be able to get all pf the data from the device at that interval. For example, if it takes 5msec to process a single request for data to the device and return it to the server.driver and it tales more than 1 requsst to get all the data then the server will go into what is called a continuous poll mode. where the data is allways stale so is soon as one poll cycle completes it is immediately restarted. Device polling and client updating occur on different threads so it miight take 2 plus seconds poll certain data in the device however the server will check for changed data and update the client every 10 msec. So the server updates the client as soon as it gets the data or very soon after.

1. Writes and Discrete Reads take priority over polling. If you are frequently writing to the device that will take priority of the polling which will cause it to take longer to complete. Sync Reads and Writes block all client processing until they complete. Async Reads and Writes do not block client processing but they do override data change polling.