In addition to receiving current data of an OPC UA server, the OPC UA Client can read out archives of an OPC UA server. Archive data can be transferred to the client via the OPC HDA or OPC UA interface.
Reception of variables archived
In OPC UA , all of variables have the special attribute Historizing that specified whether that tag has an archive. In the window of tag import, the attribute is displayed in the HDA column.
The HDA parameter is automatically set to TRUE in such tags when they are added to the tree.
In device properties, archives with the Historizing attribute are configured to be read out by default. The Read archive data setting is in charge of that.
If Read archive data = true, the following extra settings are available:
Number elements per cycle - number of archive records read out in one poll cycle.
Number elements per node - number of records read out from an OPC server in one request to the server. This setting allows you to split requests to the server- for instance, a value of this setting could be decreased if the server cannot return the required number of records per 1 request.
Depth of the read data at the start (days) - a depth of archive data read out at server start (by days)
Archive cycle - a tact of reading archives from the server. This setting might be used if not only archive data but current data are read out from the server. The setting allows you to read archives more infrequent, not changing a current data poll cycle.