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Entry type: Application example Entry ID: 109739594, Entry date: 03/16/2017
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Compressing of process value archives with the Swinging Door algorithm in PCS 7

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The process value archiving serves for compiling, processing and archiving of process data from an industrial plant. Uncompressed process value archives can grow fast to a big memory need. The PCS 7 Operator Station offers different methods of the compression of process value archives, for example the Swinging Door algorithm.

Requirement
Nowadays data backup is a fixed, integral part of all production processes. Data are used to ensure product quality or to find more efficient ways of production. Consequently, data backup serves the purpose of simplifying data tracking and ensuring competitiveness. Storage requirements often pose a challenge here. For instance, a small installation with 500 file variables being saved in a one-second cycle, creates 15,768,000,000 values per year. The objective is to employ a configuration of file variables that reduces the storage requirements without leading to the loss of relevant data.

Solution
With the Swinging Door algorithm, the PCS 7 process control system offers the possibility of project- and measuring-point-specific archiving via several parameters. This algorithm operates by setting a deviation Δy, and considering subsequent measured values from the starting point of the last saved value. Whether or not a new value is saved depends on whether the values lie within the pre-set tolerance band or outside it. The compression rate is dependent on the most tolerated divergence.


Advantage of the Swinging Door algorithm

  • Simple post-processing of the data, because the not archived process values can be interpolated linearly.
  • The algorithm saves a new point as soon as the variable departs from its previous linearity.
  • All non-saved points lie within the preset tolerance range.
  • All the saved values are real process values and are not calculated.
  • The memory need of the process value archive is reduced massively.        

Calculation Tool (SWD Tool)
The calculation tool for the swinging door algorithm helps you to achieve a parameterization for optimum compression without the loss of relevant data. To do this, export the data from your system and import them into the SWD Tool. Changing the parameters of the Swinging Door algorithm will show you the effect on your process value archive. This allows you to perform realistic tests of the algorithm without endangering the data.

Validity
The application example is valid from PCS 7 V8.0.

Downloads

  Compressing of process value archives with the Swinging Door algorithm (1,2 MB)
 Registrierung notwendig  Calculation Tool (85,4 KB)

Last changes
New chapter "Calculation Tool (SWD Tool)"
New download "Calculation Tool (SWD Tool)"

Additional keywords
Archiving methods

Security information
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