Hidden Periodicity in Quality Control Records

data points n

300

simulated data's approximate μ and σ

μ

0.

σ

1.

seed

0

use seed for a repeatable random sequence

periodicity

none

5

7

15

10

6

3

8

4

9

show autocorrelation function plot

Many fluctuating industrial quality control charts appear as random time series but may be hiding an underlying periodicity. While such periodicity can be practically undetectable in the raw record, it is clearly revealed in an autocorrelation plot. This is shown with simulated random records having different periodicities.