A Method of Full-Range Gas Concentration Detection Based on Multi-Frequency Ultrasonic Cross-Cycle Phase Difference Measurement

Ultrasonic technology is widely used in the field of gas detection due to its advantages of low power consumption, high speed and strong adaptability to the environment. The current ultrasonic time-of-flight (TOF) measurement method has the large measurement error caused by ringing effect, and the phase detection method can only detect the phase change within 2π of a single cycle. These problems cannot meet the requirements of certain high concentration gas detection. This paper proposes a method of multi-frequency ultrasonic phase difference measurement to solve the problem that the phase difference across multiple cycles cannot be detected, hereby realizing full range gas concentration detection, and the continuous wave detection of this method also eliminates ringing effect in TOF. The phase difference within 2π of a single period is obtained by loading a single frequency driving signal on two channels, and the phase difference of low-frequency envelope of the modulated signal is obtained by loading multi-frequency modulated signals. The total cross-cycle phase difference can be obtained by combining the two results, and the measured gas concentration can be obtained by the relationship model between gas concentration and phase difference. The experimental results show that the average absolute error of 4% hydrogen concentration measurement is 0.12%, and the relative error of 99% hydrogen measurement is less than 5%. This method also provides a solution for extracting cross-cycle phase difference in other fields.