Feejoy Technology (ShangHai) Co., Ltd.

Sound Velocity Measurement Method of Ultrasonic Level Meter

Ultrasonic level meter is an intelligent non-contact level measuring instrument. The product has automatic power adjustment, gain control, temperature compensation, and adopts advanced detection technology and calculation technology to improve the measurement accuracy of the instrument, and has the function of suppressing interference echo to ensure the authenticity of the measurement result. The product can be widely used for measuring the liquid level of various liquids and the height of solid materials, and can also be used for distance measurement.

The ultrasonic level meter is composed of an ultrasonic probe and an electronic unit designed in one. The level gauge is installed on the upper part of the container, and under the control of the electronic unit, the probe emits an ultrasonic pulse to the object to be measured. The sound waves are reflected by the surface of the object, and part of the reflected echoes are received by the probe and converted into electrical signals. From the time when the ultrasonic wave is transmitted to when it is received again, the time is proportional to the distance between the probe and the measured object. The electronic unit detects this time and calculates the measured distance based on the known speed of sound. The level value can be obtained by subtraction.


The propagation time of the ultrasonic wave is the intermediate result of the liquid level gauge measurement. To measure the liquid level with the ultrasonic liquid level gauge, it is also necessary to know the propagation speed of the ultrasonic wave in the air. Therefore, the accuracy of the ultrasonic wave propagation speed value will greatly affect the ultrasonic level meter's measurement accuracy.

Practice has proved that no matter what empirical formula and empirical data are used to compensate the speed of sound, new errors will be introduced due to the complexity of the measurement environment and measurement methods. Therefore, the sound velocity compensation method using the measured sound velocity is considered to be a reliable compensation method.


A baffle is installed at the front end of the transmitter probe of the ultrasonic level meter. The baffle and the probe form a sound path interval with a fixed distance. This structure is called a sound path frame. When the probe emits sound waves, the baffle can reflect part of the sound waves back to the probe. After the probe receives the reflected wave, it calculates the time from emission to reception and uses the formula to calculate the speed of sound. Among them, L is the sound path length of the sound path frame, and t is the sound wave propagation time.


Using the measured sound velocity method to compensate, because the compensation sound wave is very similar to the environment in which the measured sound wave travels, and the environmental impact is basically the same, and the sound velocity is usually close, so this method is the sound velocity correction method currently used. However, in the use of this method, the sound path frame should be made of a material with a low temperature expansion coefficient, so as to avoid thermal expansion and contraction of the sound path frame due to changes in ambient temperature, which will change the sound path distance L and affect the actual sound velocity of the ultrasonic level meter.

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