Industry 4.1. Группа авторов

RF Random Forest rpm rotation per minute RUL Remaining Useful Life SFs Signal Features S/N Signal‐to‐Noise STFT Short‐Time Fourier Transform TCP/IP Transmission Control Protocol/Internet Protocol TFT‐LCD Thin‐Film‐Transistor Liquid‐Crystal Display WPT Wavelet Packet Transform

Appendix 2.B ‐ List of Symbols in Equations

F s	sampling rate for acquiring a signal
F B	highest frequency component contained in a signal
M	number of precision items
N	data length of discrete signals
s[i]	ith data point of a discrete signal
p	pth precision item		raw sensor data of pth precision item		cleaned sensor data of pth precision item
g[k]	DWT low‐pass filters
h[k]	DWT high‐pass filters
L	number of decomposition levels;
j	scale parameters
n	translation parameter
cj[n]	nth discrete wavelet coefficient of at level j		nth approximation coefficient at level j		nth detail coefficient at level j		nth modified wavelet coefficients at level j		nth modified approximation coefficient at level j		nth modified detail coefficient at level j
λ	threshold of cj[n]
MAD(cL − 1[n])	mean absolute deviation of cL − 1[n]		modified approximation coefficients
avg	arithmetic mean or average of
std	standard derivation of
max	maximal magnitude of
min	minimal magnitude of
ptp	peak‐to‐peak amplitude of
kurt	kurtosis for measuring the peakedness of
skew	skewness for measuring the asymmetry of
RMS	root mean square value of
CF	crest factor of
T	duration of a continuous‐time signal
t	specific time t of a continuous‐time signals
cr xy	correlation coefficient value of two signals: x(t) and y(t)
CR xy