Compression filtering
When a new snapshot arrives, the previous one is evaluated according to the compression information to check whether it is a significant event. If so, it is sent to the event queue. Otherwise, it is discarded. The result is that only significant data is written to the archive. This process is called compression.
The Compression filtering group contains the following point attributes:
Use this attribute | To |
|---|---|
Compression On | Activate the compression for the point. The compression should be activated for all real-time points in the system. If the compression is deactivated, all values sent to the snapshot subsystem are saved in the archive. |
Compression Min | Set a value indicating that events are archived when the elapsed time since the previous event is greater than or equal to the minimum time, and the event value has changed by more than the deviation. Compression Minimum sets a minimum limit on the time between events in the archive. Typically, the minimal compression should equal 0. |
Compression Max | Set a value indicating that events are archived when the elapsed time is greater than the maximum time. Compression Maximum sets a maximum limit on the time between events in the archive. The recommended maximum time specification is one work shift (such as eight hours). Duplicate values will be archived if the elapsed time exceeds the Compression Max value. Under no circumstances does this cause the FactoryTalk Historian ME server to generate events; it only filters events that are externally generated. |
Compression Deviation | Set a value for the compression deviation. If you set the value too low, too little compression is imposed on data and a lot of space is wasted in the archive. If you set the value too high, you may lose important data. For most flows, pressures, and levels, use a deviation of 1% or 2% span. For temperatures, the deviation should usually be one or two degrees. |
The following are value ranges that you can use to specify parameter values:
- The Compression Deviation range is between 0 and 100.
- The range of Compression Min Day and Compression Max Day is between 0 and 100.
- The range of Compression Min Hr and Compression Max Hr is between 0 and 23.
- The range of Compression Min Min and Compression Max Min is between 0 and 59.
- The range of Compression Min Sec and Compression Max Sec is between 0 and 59.
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