Table 1.

The mathematical expressions of the six features.

Serial number	Feature name	Abbreviation	Mathematical expression
1	Mean value	MVAL	MVAL=(1/k)∑n=1kxn
2	Root mean square	RMS	$\text{RMS}=\sqrt{\left(1/k\right){\displaystyle {\sum }_{n=1}^k{\left(x_n\right)}^2}}$
3	Third moment	TM3	TM3=(1/k)∑n=1k(xn)3
4	Simple square integral	SSI	SSI=∑n=1k(xn)2
5	Logarithm	LOGD	LOGD=e(1/k)∑n=1k(xn)
6	Standard deviation	STD	$\text{RMS}=\sqrt{\left(1/k\right){\displaystyle {\sum }_{n=1}^k{\left(x_n-\text{MVAL}\right)}^2}}$