Ultrasonic measurements are mostly based on the determination of the transmission time of waves, the measurement accuracy of transmission time directly impacts the final detection accuracy. The traditional phase difference measurement of transmission time only considered the error by Gaussian noise, based on this, the influence of A/D quantizing error was considered. Using error theory, the sine signal A/D quantizing error was deduced, and the final root mean square (RMS) formula of tola] error was presented. For the two cases that the ultrasonic frequency was known and known, the method of phase difference based on fast Fourier transform (FFT) and the method of phase difference based on all phase FFT (apFFT) were analyzed and compared with. To avoid the interference of circuit and sensors, the double homologous sine sending signals with different transmission distance was used. Theory and simulation results showed that, when signal frequency was known, the phase difference based on FFT had a good result. When signal frequency was 40 kHz, Signal Noise Ratio (SNR) was 25 dB, sampling points was 2048,A/D bits were 11 bits and the sampling rate was 200 kHz, the error of the measurement of transmission time was less than 10 ns. When signal frequency was unknown, the phase difference based on apFFT had a good result.%许多超声检测都需要通过测量超声波的传输时间来实现,传输时间的测量精度直接影响了最终的检测精度.传输时间的传统相位差测量只考虑了信号传输高斯噪声误差,在此基础上,考虑了A/D量化误差所带来的影响.应用误差理论,推导了正弦信号A/D量化误差,并得到最后的总误差均方根公式.针对超声波信号频率已知和未知两种情况,分析比较FFT相位差法和全相位FFT相位差法.为了避免电路和传感器的干扰,采用传输距离不同的同源双路正弦发送信号.理论和仿真结果均表明,在已知信号频率时,FFT相位差法综合效果好,当信号频率为40kHz,信噪比为25dB,采样点数为2048,A/D位数为11位,采样率为200kHz时,测量时间误差小于10ns.在信号频率未知时,全相位FFT相位差法综合效果好.
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