# Evaluation of the Acceleration Vibration Signal for Aggregates of the Horizontal Drilling Stand
## 4 Experimental Results and Analysis
### Vibration Signal Processing in the Frequency Domain
This frequency band contains several dominant frequencies closely related to the operation of the motor and pump, motor, and hydro-generator unit combination. The spectrum of these modes was confirmed to be broad-spectrum. The spectrum of the operating mode VI, which represents the operation of the combination of pump and hydro-generator units, is influenced by the strong periodicity of the measured vibration signal. Therefore, it contains the low frequencies of revolutions and its non-integer multiples (see Figure 9f). From amplitude-frequency spectra for operating modes VII. and VIII., when all three aggregates are in operation, i.e., motor, pump, and hydro-generator, it is clear that significant frequency components are located in the frequency band 0-4000 Hz. In addition, the spectra contain several dominant frequencies and clusters (see Figure 10a,b). The spectrum of the operating mode IX. (i.e., direct disintegration of the andesite rock), contains besides the frequency band 0-2000 Hz with its dominant frequencies, also a strong  
Figure 9: Resulting amplitude spectra for the operating modes I–VI. (**(a)** frequency amplitude spectrum of the motor vibration signal, (**b**) the pump vibration signal, (**c**) the hydro-generator vibration signal, (**d**) the motor and pump vibration signal, (**e**) the motor and hydro-generator vibration signal, (**f**) the pump and hydro-generator vibration signal). frequency band 6000-9000 Hz. This significant band suggests that this is the part of the spectrum that directly identifies the disintegration of the andesite rock (see Figure 10c). The presented frequency spectra make it possible to identify and recognize individual dominant frequencies for each mode. Table 2 lists the common and different frequencies. Common frequencies are in the lower frequency band 0-1000 Hz, and differences in the 1000-3000 Hz are visible in the middle frequency band. The most significant differences are in the higher frequency band 4000-9000 Hz. Mainly frequency \(f\) = 4000 Hz, which occurs in I, IV. V. VII, VIII. operating modes do not appear in II. III. VI without the motor. From a scientific and professional point of view, we are most interested in those frequencies that can be directly identified and, at the same time, are different. It is assumed that they characterize the individual aggregates during operation, the andesite rock disintegrating mode, and other random vibrations. Power spectra are constructed during the analysis of a broad-spectrum vibrational signal with stochastic components in the frequency domain. Frequency amplitude spectra \(|X(j\omega)|\) created by the FFT algorithm are raised to the second power, which gives the \begin{table}
\begin{tabular}{l c c c c c c c c c c c} \hline \hline
**Operating Mode** & & & & & & & & & & & & \\ \hline
1. motor & 52.73 & 149 & 386.7 & 483.4 & 958 & 1274 & 1336 & - & - & 1608 & 2004 & 4000 \\
2. water pump & 52.73 & 149 & 246.1 & 448.2 & 747.1 & - & - & - & - & - & - \\
3. hydro-generator & 52.73 & 149 & 246.1 & 448.2 & 553.7 & 747.1 & 878.9 & 1318 & - & - & - & - \\
4. motor and water pump & 52.73 & 149.4 & 439.5 & 583.7 & 676.8 & 988 & 1248 & 1529 & 1652 & 1723 & 1991 & 4000 \\
5. motor and hydro-generator & 52.73 & 149.4 & 43.9 & 668 & 958 & 1230 & 1362 & 1485 & 1723 & 1995 & 4000 & - \\
6. water pump and hydro-generator & 52.73 & 149.4 & 246 & 351.6 & 448.2 & 553.7 & 747.1 & 1318 & - & - & - & - \\
7. motor, water pump and hydro-generator, tool spindle without the bit & 52.73 & 149.4 & 439.5 & 668 & 958 & 1213 & 1362 & 1494 & 1670 & 1819 & 2004 & 4000 \\
8. motor, water pump and hydro-generator, tool spindle with the bit & 52.73 & 149.4 & 386.7 & 553 & 668 & 905.3 & 1222 & 1424 & 1644 & - & 2013 & 4000 \\
9. andesite drilling & & 52.73 & 149.4 & 254.9 & 474.6 & 650 & 870 & 984 & 1292 & 1512 & - & 2004 & 6000–9000 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dominant frequencies. Figure 10: Detailed view of dominant frequencies in operational modes VII.–IX.