Data Structure Of The Opc Hda Server - Siemens SIMATIC PCS 7 Function Manual

The OPC HDA server supports the OPC Historical Data Access 1.20 specification. This was
confirmed by the compliance test. All OPC HDA clients complying with the OPC Historical Data
Access 1.20 specification can access the OPC HDA server. The use of individually
programmed OPC HDA clients is the best way to meet the requirements.
Using the OPC HDA client
There are numerous potential applications for an OPC HDA client. The following uses are
possible:
● Analysis and evaluation of archived data.
● Static process control via archives from various OPC HDA servers.
Rules
If you request historical values with the OPC HDA client, remember the following during
configuration:
● Select the cycle for a query so that the client has received the requested data before the
● The CPU load of the PCS 7 OS server depends on the number of variables per query.
6.4.3

Data structure of the OPC HDA server

Data structure
The data of the OPC HDA server is structured. The following table describes the data structure.
Element
Raw Data
Attribute
Aggregate
StartTime/EndTime
Bounding Values
Item Handle
ItemID
OpenPCS 7
Function Manual, 05/2012, A5E02780178-02
next query starts. If the cycles are too short, the result can be a large time offset when
receiving the data.
Description
The raw data is the data transferred from the PCS 7 OS archive system for
a specified period. This data has a time stamp and a quality.
Return additional quality characteristics of the raw data. Attributes include
data type, information on archiving. Additional information is available in the
section "Overview of the supported attributes".
Return a single value based on the raw data of a particular period. Aggregate
functions include average value, minimum and maximum. Additional
information is available in the section "Overview of the supported aggregate
functions".
Specify the start and end time for the period.
Bounding values are the values recorded at the start and end time. If these
do not exist, the values closest to the time are used as the bounding values.
The item handle is a unique assignment to a PCS 7 OS archive tag.
The ItemID is the unique identification of the PCS 7 OS archive tag. An item
handle can be fetched using the ItemID.
6.4 OPC Historical Data Access (OPC HDA)
OpenPCS 7 interface
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