Abstract When realizing the process control of modern industry such as chemistry, petroleum, metallurgy and water processing, we need to detect the liquid level in the container. The veracity and time are important to realizing the production safely and effectively. The existing ultrasonic liquid level meter systems make use of square pulse signal to work. Most of them have large blind zone and can not resist noise effectively. SCM is generally used to achieve the hardware realizing. The simple control system is not suitable for plex industrial production. So a new research on ultrasonic liquid level meter is necessary. LFM is a kind of time-varying signal with large time and broadband characteristics. It has good precision and distance-distinguished capacity and has been widely used in the area of radar and sonar systems. This paper applies the LFM technology to the detecting and reduces the blind zone effectively. We have two achievements as below. Firstly, we estimate the parameters of LFM using joint time-frequency analysis and research Cohen time-frequency distribution. We use Hough transform to solve problem of cross item in time-frequency processing. The simulation shows it has excellent time-frequency assembling and antinoise characteristic. It can also restrain cross item well. The result is better than short time Fourier transform and Wigner-Ville distribution. Secondly, we analyze the work elements of ultrasonic liquid level meter and the cause of blind zone. We put forward the configuration of ultrasonic liquid level meter. We also apply DSP and high speed AD to ultrasonic liquid level meter to solve the contradiction of reducing blind zone and extending measure range. The simulation results show that the application of LFM can enhance the measure precision and confirm the interface of different kind of liquid effectively. Furthermore, it can reduce the range of blind zone. Keywords Ultrasonic; Liquid level meter; LFM signal; pression; Joint time-fr
