In case of a time-based HD data store, the signals are saved continuously through time in an HD store on the HD server. Similar to a usual ibaPDA data store, the signals to be stored have to be selected and assigned to a store profile. For the time-based data store, all signal types, including text channels, can be used.

For the display of time-based HD data, the view HD trend graph is available in the ibaPDA client and in ibaQPanel. Text channels can be displayed in the HD trend graph. To guarantee a quick and user-friendly display, also for large data volumes or the presentation of long periods of time in ibaPDA, the files are stored in a special file structure with several consolidation levels. According to the set time base for the data acquisition up to 6 aggregation levels are used. From level to level, for each signal 40 samples are combined to a sample group consisting of average, minimum and maximum value of the 40 basic values. Therefore, every new aggregation level contains only approx. 2.5 % of the samples of the last level. The creation of further aggregation levels is only continued as long as the distances between the aggregated measuring points are at least 1 day. You can customize the preset aggregation levels in the profiles in ibaPDA, see Define data storage profiles.

Text channels are saved with other aggregation levels: Original time base, 5ms, 3 min: 20 s, ca. 2 h and approx. 88 h.

The zoom in the signal curve is considerably accelerated by this scaled storage method.

The following figure shows the principle of data aggregation or, conversely, drill-down.

Examples

Measuring point distance

Aggregation

Time base = 1 ms

Time base = 10 ms

Time base = 50 ms

Level 1

40 ms

400 ms

2000 ms (2 s)

Level 2

1600 ms (1.6 s)

16,000 ms (16 s)

80,000 ms (1.3 min)

Level 3

64,000 ms (1.1 min)

640,000 ms (10.67 min)

320,0000 ms (53.3 min)

Level 4

2,560,000 ms (42.7 min)

2,560,0000 ms (7.1 h)

128000000 ms (1.5 d)

Level 5

102,400,000 ms (1.2 d)

1024000000 ms (11.9 d)

-

Level 6

-

-

-

Level 6 or higher are only used for time bases < 1 ms.

As a supplement to this type of file reduction, the usual consolidation according to the method of the run length encoding is used so that the store capacity is only insignificantly higher than for normal data files (DAT files). The zoom in the signal curve is considerably accelerated by this scaled storage method.

The interpretation of the three aggregation values minimum, maximum and average is different for digital signals than for analog signals. The average value is an indicator of the majority of the values in the aggregated period. If the digital signal has a high value for over 50% of the time period, then a high value is stored in the aggregation level and vice versa. This is independent of the number of signal changes. The combination of the minimum and maximum values of an aggregated time period shows whether or not the digital signal was stable in the time period. If the minimum and maximum values are the same, the digital signal stayed at the same level during the period. If not, one or more signal level changes have occurred.

With version 7.3 of ibaAnalyzer a new option Query digital signals on raw level as non-equidistant data has been added to the HD Server query settings. Using this option, it is possible to query always digital signals as raw data independent of the aggregation level and selected query time base which is used for analog values. Especially for long-time queries this makes it possible to correctly measure duration or to evaluate time stamps of value changes without the usual errors introduced by the data aggregation on ibaHD-Server.

If this option is enabled, ibaAnalyzer uses a different mechanism to query digital signals from any ibaHD-Server.

For more information, see the ibaAnalyzer manual.