Presents a study on ultrasonic velocity of medium through quadrature demodulation in order to realize the measurement of ultrasonic medium propagation speed in plastic pipe container.Some numerical tests are conducted on simulated signals and an experiment system based on STM32 single-chip microcomputer is used for real tests.The method applies a quadrature demodulation scheme to get the envelope of the digitized ultrasonic signal,and locate its TOF on a fixed distance by a method based on fitting the rising edge of the envelop.The purpose of measuring the ultrasonic velocity of medium can be ...