The delay you are seeing is how long it takes the OPC server to return the data. So, primarily this is a question you should ask your server vendor.

Related information:

The behavior also depends on the read parameters (of type DAReadParameters) passed to the ReadMultipleItems call. They can specify a) that the data will be always be read from the device, b) that the device will be always provided from the OPC server cache, or c) that the cached data will be used if "fresh enough", but that the OPC server should perform a read from the device if the data is older. By default, the "c)" option is used, with value age set to 1 second. Quite likely the server has to retrieve the data from the device, which takes time - especially if there is some problem. You can speed up things by choosing to read data from the cache, but then of course you must consider the consequences - it may not be the up-to-date data you wanted.

See also e.g.:

• www.opclabs.com/files/onlinedocs/QuickOpc/Latest/User%27s%20....DAReadParameters_methods.html
• www.opclabs.com/files/onlinedocs/QuickOpc/Latest/User%27s%20...rameters~FromDADataSource.html
• opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...AClient~ReadMultipleItems.html
• opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...ReadItemArguments_members.html
• [],DAReadParameters).html

Also note that (if your application is of that nature), it is better to use OPC subscriptions rather then repetitive reads (if you are doing them). Collecting the data would take the same time to the OPCserver, but your program is not blocked until the data is available - you are sent a notification when there is an update.

Regards