Table 7 Summary of data preprocessing techniques

Segmentation

Isolation of relevant data

The reduced computational burden for subsequent stages

Thresholds required

Subjective isolation for simultaneous PQDs

Additional equipment/processing required

[38, 42, 44, 47, 57, 59, 61, 63, 69, 72, 75, 76, 81, 89, 97, 99, 101, 108, 124, 128, 130]

21

[159, 162, 168, 174, 175, 184]

11

[191, 194, 195, 202, 205, 207, 211]

28

Denoising/filtering

[62, 91, 102, 126, 128, 130]

6

[141, 152, 175]

5

[188, 199, 204, 208]

16

Normalization

Amplitude-independent techniques

Thresholds in the percentage of the original signal

Interpretation of results is relative

Loss of real-signal amplitude features

[42, 48, 50, 54, 55, 58, 59, 64, 68,69,70,71,72, 74, 76, 80,81,82, 88, 91,92,93, 97, 98, 101, 103, 108,109,110,111, 115, 119, 120, 122]

34

[140, 141, 143, 144, 146,147,148, 150, 152,153,154,155,156,157,158,159, 161, 162, 164,165,166, 168, 181, 182]

44

[209, 211]

8