You can Display a Historic List for an individual point that has Historic Logging enabled, or for an individual master station accumulator.
Each Historic List comprises a series of rows and columns, and contains the data that is stored historically in the ClearSCADA database for that particular point or accumulator. Each row comprises the data for an individual historic record. The column headings indicate what the data in each column represents.
Be aware that ClearSCADA supports historic data compression, whereby unnecessary data can be filtered out so that only those entries that are of interest are stored historically. Compression is mainly used to reduce storage requirements for historic data, and is typically used with points on simple drivers rather than advanced drivers. For more information on compressing point data, see Historic Data Compression. For information on compressing accumulator data, see Tabs on Accumulator Forms. There are some updates to which compression settings do not apply—ClearSCADA logs such updates historically regardless of any compression settings (see Point Updates to which Compression Settings do not Apply and see Accumulator Updates to which Historic Data Compression Settings do not Apply). You can determine why ClearSCADA has stored an update historically by looking at the Historic List for the point or accumulator. The column headings for a Historic List are:
- Time—The date and time at which the data was recorded.
There are many factors that affect the time stamp of a record, primarily the driver. With some drivers, the outstation time stamps the data and then passes that data to ClearSCADA. With other drivers, the time stamp might be generated by the outstation or the server, depending how the data was reported. Outstations on some drivers do not support time stamping of data, and therefore the server time stamps that data when it receives it from the outstation. Historic records that are logged due to actions such as Override and Release Override are time stamped by the server.
- Value—The recorded value of the point or accumulator.
- State—The recorded state of the point or accumulator.
- Quality—A description of the quality of the data. This indicates the reliability of the data. Descriptions within this column might include:
- Good—The quality of the data that has been logged is good.
- Local Override—The data that has been logged is for a value that has been locally overridden at the ClearSCADA server. (Some drivers also support overriding of point values at the outstation.)
- High : Engineering Units Exceeded—The data has been logged while an analog point was over range (the value exceeded the point’s Full Scale limit).
- Low : Engineering Units Exceeded—The data has been logged while an analog point was under range (the value was below the point’s Zero Scale limit).
Most drivers only map to a subset of OPC qualities, depending on what information they are capable of reporting. The reason for a historic record having a particular quality is typically down to the individual driver and how it maps the information available to it onto the standard OPC qualities. For a more comprehensive list of Quality values, see Quality.
- Reason—The reason why the data is being stored (‘logged’) historically. Possible reasons for logging include:
- Current Data—The data has been logged due to a request for the point or accumulator’s current data.
- Value Change—The data has been logged due to a significant change in point or accumulator value. (Typically due to a change in value exceeding a Significant Change deadband, although some drivers interpret value changes differently.)
- State Change—The data has been logged due to a change in point state.
- Timed Report—Only applies if timed reporting (‘background Logging’) is supported by, and configured for, the point or accumulator. The data has been logged due to the timed report interval expiring.
- End of Period—Only applies if End of Period reporting is supported by, and configured for, the point or accumulator (see End of Period). The data has been logged due to the End of Period report interval expiring.
- End of Period Reset—Only applies if resetting of values at an End of Period interval is supported by, and configured for, the point or accumulator (see End of Period). The data has been logged due to an End of Period reset.
- Override—The data has been logged due to the point’s value being overridden.
- Release Override—The data has been logged due to an existing Override being released.
- Modified/Inserted—The data was either inserted or modified.
The Insert/Modify Data option can be used to insert or modify a point or accumulator value on a Historic Trend. The Modify Range of Values option can be used to modify a 'block' of point values on a Historic Trend. These options are useful if data was not recorded for some reason, or values that have been recorded historically are inaccurate (for instance, due to an instrument fault). For more information, see the ClearSCADA Guide to Trends.
The reasons for logging vary, depending on the type of driver and point, the features they support, their configuration, and so on. If you intend using a point as the source of a master station accumulator, you can use the Reason column on the point's Historic List to ascertain the reasons for which ClearSCADA is storing the point's data. You can use this information to help determine which check boxes you should select in the 'Source Object' section of the Accumulator Form, in order for the accumulator to process the relevant values from that point source. For more information, see Specify an Accumulator’s Source in the ClearSCADA Guide to Core Configuration.
- Status—A description of the status of the data, as a comma- separated list. Applies to Historic Point Lists only. A Status entry might indicate, for instance, that:
- The point was overridden at the master station (ClearSCADA server). (Advanced drivers only.)
- The time that the data was recorded was in the future. (Advanced drivers only.) Such a status indicates that the data is from a device that has different time settings to the server. For example, an outstation that has not had its clock set correctly, or that has a clock which is fast. For more information, see Define the Maximum Outstation Clock Drift.
A driver-specific status description might be displayed for points on some drivers.
- Suppression Type—Indicates whether the data relates to alarms being suppressed or unsuppressed. Applies to Historic Points Lists only. The possible values are:
- Consequential—The data is associated with the ‘Consequential’ type of alarm suppression.
- Maintenance—The data is associated with the ‘Maintenance’ type of alarm suppression.
- None—The data is not associated with alarm suppression.
For further information on alarm suppression, see Alarm Suppression.