On-line Process Analysis by the EVOP Method

On-line investigation methods for statistical analysis are used when the performances of a continuous process carried out in a pilot unit or in an apparatus, have to be improved. The Evolutionary Operation Process (EVOP) method [5.7, 5.27, 5.28, 5.31] is the most famous method for on-line process analysis. The name of this method comes from its analogy with biological evolution. This analogy is based on the observation of the natural selection process in which a small variation in independent life factors is responsible for genetic mutations and thus for the evolution of species. 

The number of cycles for each stage must be thoroughly selected because then the interest is to observe the small changes occurring simultaneously with the permanent random fluctuations in the process output. The data from a cycle are transferred to the next cycle to complete the new phase by calculation of the mean values and variances. It is well known that the errors in the mean value of n independent observations are s/n smaller than the error of an isolated measure. Therefore, this fact sustains the transfer of data from one cycle to the next one. 

For each phase, the number of cycles is not imposed by a rule or by a mathematical relation. 

At the beginning of the second cycle, the calculation of the total effects of the analysis is obligatory the total effects in 

each yf value is the mean value for all the cycles carried out with respect to the actual phase of the analysis. 

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