Principle and classification of ultrasonic level gauge

by:Kaidi Sensors     2022-09-29
Ultrasonic level gauge is a common level gauge, so what is its working principle? What are the types (classifications) of ultrasonic level gauges? Ultrasonic liquid level gauges use the propagation characteristics of waves in the medium. Specifically, when the ultrasonic wave encounters the phase interface during propagation, part of it is reflected back, and the other part is refracted into the adjacent medium. But when it propagates from gas to liquid or solid, or from solid or liquid to air, almost all reflection occurs due to the large difference in medium density. Therefore, the ultrasonic transmitter and receiver are installed at the bottom or top of the container, and the emitted ultrasonic waves are reflected at the phase interface and received by the receiver, and the liquid level can be measured by measuring the time difference between ultrasonic wave transmission and reception. According to different sound transmission media, ultrasonic level gauges can be divided into three types: gas-mediated, liquid-mediated and solid-mediated. Combined with each other, six types of liquid level gauge solutions can be obtained. Figure 1 shows a single-probe ultrasonic level gauge. Among them, (a) is gas-mediated, and (b) is liquid-mediated. (C) is solid medium type. In actual measurement, sometimes there will be bubbles, suspended matter, waves or boiling on the liquid surface, which will cause reflection confusion and measurement errors. Therefore, solid-medium level gauges should be used in complex situations. It does not produce reflection confusion or beam deflection for the reasons mentioned above. (a) gas-mediated type (b) liquid-mediated type (c) solid-mediated type device. The dual-probe type uses two transducers as transmitter and receiver respectively. For the solid medium type, two metal rods or metal tubes are required as transmission pipes for transmitting waves and receiving waves, respectively. It can be seen from Figure 1 that the ultrasonic propagation distance is L, the propagation speed of the wave is C, and the propagation time is Δt, then (1) L is a quantity related to the liquid level, so the liquid level can be known by measuring Δt, Δt The measurement is generally realized by using the received signal to trigger the gate circuit to count the pulses of the oscillator. Ultrasonic liquid level measurement has many advantages: ① No contact with the medium, no moving parts, electronic components only vibrate at sound frequency, small amplitude, long life of the instrument; ② Ultrasonic propagation speed is relatively stable, light, medium viscosity, humidity, dielectric constant , electrical conductivity, thermal conductivity, etc. have almost no effect on detection, so it is suitable for liquid level measurement in special occasions such as toxic, corrosive or high viscosity; Signal; ④ It can measure the liquid level of liquids that move at high speed or tilt and shake, such as the liquid level in cars, planes, and ships. When the temperature or density of the ultrasonic propagation medium changes, the speed of sound will also change, and the ultrasonic level gauge should have corresponding compensation measures, otherwise it will seriously affect the measurement accuracy. In addition, some substances have a strong absorption effect on ultrasonic waves, and the specific situation and conditions of liquid level measurement should be fully considered when selecting measurement methods and instruments.
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