Ultrasonic liquid level measuring technology has been extensively applied in the industrial field, which is characterized by its high accuracy, strong ability of anti-electromagnetic interference and simple structure. However, its measurement results are easily affected by the tilt of liquid level and ripple. In this study, the traditional gas-liquid interface was transformed into a solid-liquid interface based on the acoustic scattering by a rigid sphere and a circular waveguide, and the liquid level was measured with the stable reflecting surface by complying with the liquid level in the duct. Such a method could overcome the effect of the tilt of liquid level and ripple on the measurement results. In this study, a signal processing method to improve the signal to noise ratio of the direct wave was proposed. To improve the sound intensity of the direct wave and reduce the effect of high-order mode waves on the signal, the transceiver was applied with a matching layer, and the appropriate waveguide material should be selected to absorb a portion of high-order mode waves. As revealed from the experimentally achieved results, an optimized lightweight ultrasonic liquid level sensor was proposed to eliminate the effect of ripple, and the tilt of liquid level increased from 20° to 60°. 

An Optimized Lightweight Ultrasonic Liquid Level Sensor Adapted to the Tilt of Liquid Level and Ripple

Smartphone-integrated notch POF sensors with two different types (U-shaped and spiral) are demonstrated in this paper for liquid level and RI monitoring. The level and RI changes are measured by the loss of light intensity due to the notch on the POF fabricated from 3D-printed cut molds. The effects of different notch depths for two sensor types are explored. The highest sensitivity of the sensors we presented here can reach 0.59 %/cm in U-shaped type in level monitoring and 107.6 ± 4.4 %/RIU in U-shaped type in RI monitoring. The two sensor types respond differently to the notch depth, resulting in their different range of applications. Taking advantage of easy fabrication, low-cost and equipment requirements, customizable with two types, portability, and convenient real-time analysis, the sensors have promising prospects for industrial or agricultural monitoring. 

Notch POF integrated with smartphone for liquid level and refractive index monitoring

Measurement of the small filling levels in closed steel container systems is still a challenge. Ultrasound, however, is a sensitive and non-invasive technique and is suitable for online monitoring. This study describes a new ultrasonic sensor system for sensing small filling levels using longitudinal and surface acoustic wave analysis. The sensor system consists of one transducer for the longitudinal wave analysis and two transducers for the longitudinal and surface acoustic wave analysis. All transducers were mounted to the outer wall of the steel container, ensuring non-invasiveness, and a filling level ranging from 0 to 5 cm was investigated. Combining both approaches, a consistent determination of small filling levels was achieved for the entire measuring range (R2 = 0.99).

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Combined Longitudinal and Surface Acoustic Wave Analysis for Determining Small Filling Levels in Curved Steel Containers

We report a liquid-level sensor composed of a laser, prism, and photodiode array. The sensor does not require components, such as a sensor head, inside the container that stores liquid. The sensor detects the liquid level based on the difference between the intensities of laser light reflected at the liquid/glass and air/glass interfaces. As the detected liquid level shows a shift from the correct liquid level owing to surface tension and the broadening of the laser light, we correct the shift through calculations. The sensor can be attached to a flange-type glass viewport, providing compatibility with broad-ranging containers for industrial use. The sensor can accurately detect the liquid level with a maximum error of 0.3875 mm. We demonstrate the implementation and operation of the liquid-level sensor in a wireless system comprising a sensor head and wireless voltmeter. The reported sensor allows accurate measurement of the liquid level in a tank inside which foreign objects such as sensor heads cannot be installed. 

Flange-type liquid-level sensor based on laser light reflection

This Letter presents an ultrasonic waveguide sensor for measuring fluctuations in a liquid level using leaky longitudinal wave L(0,2) in a coolant loop system. A 20% cold-worked D9 fuel pin clad tube of 1000 mm long, 6.6 mm outer diameter and 0.45 mm wall thickness was used as a waveguide on which the L(0,2) mode was transmitted/received along the axial direction at 500 kHz. When the waveguide got introduced into a coolant loop and partially immersed in a non-viscous liquid (water/liquid sodium), the amplitude of L(0,2) mode got reduced due to leakage. The rate of leakage depends on the characteristics of the waveguide and the embedding liquid medium. By utilising this physical property of L(0,2) mode, it is possible to predict the variations in liquid level during dynamic conditions. Experimental measurements were carried out on a mock-up test loop in which water was used as embedding liquid and two artificial notches were made on the waveguide at different depths were used as reference levels. The time-amplitude signals were monitored and the reflected energies from the bottom end of the waveguide and the notches were used as the threshold and reference amplitudes respectively for identification of water level.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/el.2020.1678

S. Manivannan

Papers

Development of ultrasonic waveguide sensor for liquid level measurement in loop system