In the paper the real-time system based on FPGA applied to control the delay time in feedback loop of the Self-excited Acoustical System is presented. The system can be used for stress change measurement in elastic constructions. Stress changes manifest themselves in small but detectable variations of resonance frequency. This phenomenon can be used to indirect measure stress changes in the material. In the article the limits of the measurement system which occurred during research on the analogue version of the system were eliminated by applying FPGA technology.