NOTE: High speed data sampling is only available for Analog Input points, and is only available in WITS version 1.3 or later.
The WITS standard provides for high speed data sampling. This means that the Field Device may have the capability to sample and store data at a faster rate than the standard WITS periodic logging rate. Where this feature is enabled, there is a store for each analog input point. You can define the size of each store as a number of weeks, days or hours (although the size may be fixed in the device profile - see Display a WITS Device Profile). When a store is full, the Field Device will overwrite the oldest existing data. You can also specify the rate at which the Field Device will sample the analog input point.
Example:
If you specify a store size of 7 days, the Field Device will sample and store data for 7 days. After 7 days, it will start to overwrite that data with new data for another 7 days. It will continue to store and overwrite data in a 7-day cycle. Therefore, the store will always hold data for the previous 7 days.
NOTE: Due to memory constraints, there may be restrictions on the number of points for which you can do high speed data sampling.
Example:
The Field Device may support high speed data sampling for:
- All analog input points
- A maximum number of analog input points
- A specific list of analog input points
- Some other combination of points.
The device profile defines the level of support for high speed data sampling (see Display a WITS Device Profile).
This high speed data sampling capability might be helpful when an unexpected system event occurs. You can then investigate the event by reading specific sampled data from around the time that the event occurred. You can:
- request data for a specific point
- request data for all points
- request data between specific times.
For more information, see Retrieve Sampled Data (WITS Outstation) and see Retrieve Sampled Data (WITS Point)
NOTE: When you retrieve standard logged data, ClearSCADA will not retrieve sampled data as well (see Specify the WITS Properties and see Refresh). You must specifically request the sampled data stored by the Field Device.
Use the fields within the High Speed Sampled Data section of the Input tab to specify the high speed data sampling properties.
The fields are as follows:
- Enabled—Select the check box to enable high speed data sampling. Clear the check box to disable high speed data sampling.
- Sampling Rate—Specify how frequently the Field Device should sample the analog input point. You should choose a sampling rate that is supported by the Field Device. The device profile defines the sampling rates supported by the Field Device, as well as the lowest resolution it supports ((see Display a WITS Device Profile)).
Enter the rate directly in the field (use the OPC Time Format) or use the Interval Window (accessed from the field's browse button).
- Cycle Store Size—Specify the size of the data store.
Enter the value directly in the field (use the OPC Time Format) or use the Interval Window (accessed from the field's browse button). The device profile defines the sizes supported by the Field Device ((see Display a WITS Device Profile)).
NOTE: The high speed data sampling properties may be fixed in the Field Device, so you may not be able to download changes to them. The device profile defines any fixed properties (see Display a WITS Device Profile).