Liquid level detector for a sealed gas tank based on spectral analysis

Abstract

While several methods using ultrasonic, acoustic or RF waves have been proposed to measure the liquid level of a sealed container, they all need to install a transmitter and receiver pair inside the top of the tank. In this paper, we propose a simpler method which provides continuous measurement by installing a knocking device outside the tank. The vibratory frequencies generated by the knocking action are analyzed by the fast Fourier transform and the dominant frequency component which is related to the liquid level inside the tank is acquired. Our experimental results show that relationship between the vibratory frequency generated by the knocking action and the liquid level can be described by Bernoulli-Euler beam theory. Therefore, this acquired relationship can be used to estimate the liquid level based on the spectrum generated by knocking the tank surface.

Analysis and Implementation of Noncontact Level Sensing for a Pressurized Cylinder

“…The goal of the conducted experiments was to tabulate the total weight of the gas tank and its homologous dominant frequency of vibration after being knocked, that is ( , [ ]). Computation of the dominant frequency can be found in [17]. Given this particular cylinder, the occurrence of this frequency fell between 700 Hz and 900 Hz.…”

Portable and Non-Intrusive Fill-State Detection for Liquid-Freight Containers Based on Vibration Signals

“…To reduce the energy attenuation in propagation, the excitation generated by the transmitter only travels a small distance instead of penetrating the whole container. Here, the literature indicates that the Lamb wave mode [ 16 ], the resonance frequency [ 17 , 18 , 19 ] or the spectral peak amplitude [ 20 ] is affected by the presence of liquid and may be used to deduce the liquid level. Detection criteria can be deduced from a physical model of the impulse response of the container.…”

“…[ 18 ] estimates the peak frequency shift during liquid loading by finite element method (FEM) for a standing cylindrical container with constraints applied to its base. The approach of [ 19 ] adopts a simplified model, the Euler-Bernoulli beam theory, and yields a similar relationship between the peak frequency and the weight of its content when assuming the container is constrained at both ends. However, these physical models are heavily dependent on the geometry and material characteristics of containers, and the calculation could be too complex to transfer established models to unseen ones.…”