Preliminary signal filtering in Self-Excited Acoustical System for stress change measurement

The article describes the implementation of low pass Buttherworth digital filter in Self-Excited Acoustical System for measurement of stress changes in mechanical constructions and rock masses. The Self-excited Acoustical System (SAS) is a kind of a self-oscillating system, which uses the auto-resonance phenomena for measurement of construction stress changes. The essence of the SAS system is to use a vibration exciter and vibration receiver placed at a distance with a positive feedback, which causes the excitation of the system. Stress changes manifest themselves in small but detectable variations of frequency. This phenomenon can be used to indirectly measure stress changes in the material. One of the main problem of this innovating system is quality of the measured noised signals, which is difficult to interpret. To enhance the self-excited system performance the preliminary signal filtrating is introduced.