DC Systems

RTscada: Historian

Historical Data Subsystem

One of the advanced features of the RTscada system is the historical data subsystem. It is used to record real-time data, as it occurs, with millisecond time tags.

History data is archived by the Historical Data Recorder. The data is stored in a streaming disk file, with a separate file for each calendar day. A separate index file is used to provide quick access for data retrieval. Periodic checkpoints record all values, for use as a starting point in the retrieval process.

Analog points feature a unique three-part changeband/time system which provides complete flexibility in configuring the recording of analog values. Analog values can be recorded as they change, at pre-defined time intervals, or with two different levels of changeband, depending on the time interval since the last value archive. Both value and state changes are archived for all point types. State changes include changes such as com fail, alarm inhibit, control actions, tagging, etc.

History retrieval is provided by the Historical Data Server. This multi-threaded program processes requests for history data from various clients. It retrieves the requested data and then forwards it to the requesting client via the network.

Several playback methods are provided:

• Graphs in the user interface may be populated with history data. The user may then toggle between the real-time and historical data.
• The user interface supports history playback of the data which occurred during a user selectable time period. In event mode, the user can single step through each event, one event at a time, with millisecond accuracy. This mode is useful for outage reconstruction and post-disturbance analysis. In time mode, data can be played back with variable speed, between 1/10 real-time and 10x real-time. VCR-type buttons provide play, stop, and rewind functions.
• The History Export Wizard exports history data into an ASCII, comma-delimited file, which can be easily imported into an Excel spreadsheet. The user can specify the data points, time span, and data increment for the exported data. In addition, an event mode exports all data as changes, rather than a time series.