Function and principle of ultrasonic level gauges

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Abstract: An ultrasonic level gauge is a non-contact liquid level measuring device that is resistant to corrosion by various types of wastewater, allowing it to be used for a long time; as a result, it is widely used. The article mainly introduces the principle, usage method, features of ultrasonic level gauges, as well as their installation requirements. 　　 　　An ultrasonic level gauge is a non-contact liquid level measuring device. It can be used to measure the liquid level and flow rate in various containers or pipes, as well as the water level in canals, reservoirs, rivers, and lakes. It is particularly suitable for use in situations involving sewage or corrosive substances, such as measuring the water level before and after the trash racks in urban drainage pumping stations. Due to the strong corrosive nature of urban wastewater, if a contact-type pressure gauge is used, the sensor probe must be inserted into the wastewater, which causes the probe to corrode rapidly and disrupts accurate measurement. In addition, ultrasonic level gauges feature high measurement accuracy and easy installation and maintenance. They can simultaneously measure levels, level differences, and flow rates, and come equipped with a standard computer interface such as RS-485; for these reasons, they are being used more and more widely. 　　 　　The probe of an ultrasonic level gauge is installed above the liquid being measured. Once powered, the probe emits ultrasonic waves into the liquid below through the air; these ultrasonic waves are reflected by the liquid, and the echoes are detected and monitored by the probe, where they are then converted into electrical signals. The time required for ultrasound to travel from transmission to reception is proportional to the distance between the probe and the liquid surface. The distance D is determined by the speed of sound C and the transmission time t, as shown in the formula: D = C·t/2. Under normal conditions, the speed of sound in air is 340 m/s; if the transmission time is 10 ms, then the corresponding transmission distance is 3.4 m, so the distance D is 1.7 m. An ultrasonic level gauge actually measures the change in liquid level height, and through presetting of the gauge, this value can be converted into the actual liquid depth. 　　 　　Sound waves are one type of sound and belong to the category of mechanical waves. They are longitudinal waves that can be detected by the human ear, with a frequency range of 16Hz to 20KHz. Sound waves with a frequency below 16 Hz are called infrasound, while those with a frequency above 20 KHz are known as ultrasonic sound waves. 　　 　　Yes, ultrasound is widely used in fields such as diagnostics, therapy, engineering, and biology. The Saifuri home-use ultrasonic therapy device falls within the scope of applications of ultrasonic therapy. 　　 　　(1) Applications in engineering: underwater positioning and communication, exploration of underground resources, etc.
(2) Applications in biology: cutting large molecules, bioengineering, and seed treatment, etc.
(3) Applications in diagnostics: Type A, Type B, Type M, Type D, duplex imaging, and color Doppler ultrasound, etc.
(4) Applications in therapy: physiotherapy, cancer treatment, surgery, extracorporeal shock wave lithotripsy, dentistry, etc.

The effects of ultrasonic waves
Cleaning glass parts and glass and ceramic products of scale can be a troublesome task. If these items are placed in a cleaning solution and ultrasonic waves are applied, the intense vibrations of the cleaning solution help to remove the dirt from the surfaces of these items, allowing for quick cleaning.
Although humans cannot hear ultrasonic waves, many animals do have the ability to detect them. They can use ultrasound to \"navigate,\" hunt for food, or avoid hazards. You may have seen many bats flying back and forth in the courtyard on summer nights; why can they fly in the absence of light without getting lost? The reason is that bats can emit ultrasonic waves in the range of 20,000 to 100,000 Hz, which functions like a mobile \"radar station\". Bats use this \"sonar\" to determine whether what is in front of them during flight is an insect or an obstacle. The weight of radars can range from dozens to hundreds or even thousands of kilograms. In terms of certain key performance aspects such as interference resistance, bats far outperform modern radio locators. By studying in depth the functions and structures of various organs in animals and using the knowledge gained to improve existing devices, a new discipline has emerged over the past few decades – biomimicry. It was not until World War I that humans learned to utilize ultrasonic waves, by applying the principle of sonar to detect objects and their conditions in water, such as the location of submarines. At this point, a series of ultrasonic waves with different frequencies are sent into the water, and the reflected echoes are recorded and processed; by analyzing the characteristics of these echoes, it is possible to estimate the distance, shape, and dynamic changes of the object being detected. The earliest medical use of ultrasound dates back to 1942, when Austrian doctor Dusik used ultrasound technology to scan brain structures ； In the 1960s, doctors began to use ultrasound for the detection of abdominal organs. Today, ultrasound scanning technology has become an indispensable tool in modern medical diagnosis. 　　 　　Proper installation of the ultrasonic level gauge is key to its reliable operation. The level gauge is installed above the container, with the transmitting surface of the probe pointing vertically at the liquid level or material surface. If it is a closed container, flange mounting should be used. In other cases, simple bracket installation can be used. Flange mounting should use flanges that match the thread size on the level gauge. 　　 　　I. Installation requirements for ultrasonic level gauges 　　　When ultrasonic waves are emitted, they have a very small divergence angle. If there are other objects within this divergence angle that block the waves, reflections will occur; strong reflections can lead to measurement errors. 　　　The installation location should be as far away as possible from uneven container walls, as well as from objects inside the container such as ladders, filling ports, and stirring blades, which can block the sound waves. 　　 　　In the case of a sealed container, the flanges on the container must meet the following requirements: the inner diameter of the flange should be greater than 120 mm, the length of the flange connections should be less than 100 mm, the inner surface of these connections must be smooth, and the lower edge should be covered with a soft plastic film. The inner diameter of the flange should be greater than 70 mm; the flange connections should be as short as possible, with a smooth inner surface and a smoothly curved lower edge. The inner diameter of the flange should be greater than 200 mm; if the length of the flange fitting is greater than 100 mm, the inner wall of the fitting must be smooth, with a smoothly curved lower edge. 　　 　　If the flange at the installation location does not meet the above requirements, and the instrument operates unstably after installation, with the liquid level value fluctuating to high values or remaining at a high level, the following method can be used to address this issue: Insert a plastic tube into the container at the flange location, all the way to the bottom of the container, and secure it firmly in place. The plastic pipe should be straight, with a smooth inner wall. One hole should be made at the top and one at the bottom to ensure that the liquid levels inside and outside the pipe are the same. The required inner diameter dimensions for plastic pipes are as follows: the inner diameter should be greater than 55 mm; for smaller measurement ranges, a value of greater than 50 mm is sufficient. It is recommended to make modifications during installation. In cases where there is significant fluctuation in the liquid level, or if there are floating objects or elements that can block sound waves, it is possible to insert a plastic pipe into the container, allowing sound waves to travel only within this plastic pipe, thereby ensuring stable and reliable measurements. 　　 　　The installation should ensure that the liquid level or material level does not enter the dead zone of the level gauge. 　　 　　If necessary, the level gauge can be installed at a higher height. The inner wall of the joining pipe used for elevation must be smooth, and its inner diameter should not be larger than that of the container’s flange opening. 　　 　　When using flange mounting, the flange provided for the level gauge should be made of plastic. The method is to specify the size of the mounting flange at the time of ordering, so that the manufacturer can prepare it directly. 　　 　　The transmitting surface of the level gauge probe should be directed vertically at the liquid surface or material surface, and it should be aligned with the target as accurately as possible during installation. 　　 　　Stay away from devices that generate strong electromagnetic interference. 　　 　　II. Wiring of the ultrasonic level gauge 　　　During wiring, the wire cover must be removed to expose the entire wiring terminal. Use a flathead screwdriver to make the connections. 　　 　　III. Operation of the ultrasonic level gauge when powered on 　　　After the gauge is powered on, it first displays “HLUC”; after a few seconds, the level value is shown, and the indicator light flashes once every second. 　　 　　The level gauge actually measures the distance from the probe to the liquid surface or material surface, and then calculates the level value; it is important to understand this principle. 　　 　　Pressing the SEL key allows you to view the distance measurement and temperature value. 　　 　　Press the MOV and SEL keys simultaneously to enter the parameter setting mode; set the installation height and range, then specify the upper and lower limits as needed. After making the settings, press the SEL key once again. Then, press the MOV and SEL keys simultaneously to return to the measurement state. The instrument will display the correct level value, and output the correct current signal as well as the high/low level switch signals. 　　 　　If the measurement is incorrect, please refer to the next section “Troubleshooting” for solutions. 　　 　　IV. Troubleshooting of Ultrasonic Level Gauges 　　　　Fault Symptoms, Causes, and Solutions 　　　　The gauge does not display or does not function: Incorrect power supply; incorrect wiring. Check whether the DC24V power supply is correct and verify that the wiring is proper. 　　　　The gauge displays but does not function: The level gauge is not aligned with the liquid or material surface; the amplitude of surface fluctuations is too large; the surface is uneven; there is a thick layer of foam on the surface; the container is empty, or the bottom of the container is not flat, causing it to be outside the measurement range. Adjust the alignment of the level gauge; use a level to make adjustments. Insert a plastic tube into the container (see the installation section). A level gauge with a larger measurement range is required. Add liquid or material to restore normal operation; use a level gauge with a larger measurement range. 　　　　The gauge’s display is unstable or the measurement values show significant deviations: The level is in a blind zone; power supply is unstable; there is strong electromagnetic interference; there are objects that block sound waves. Metal flanges are used on the level gauge, causing the probe’s transmitting surface or sides to come into contact with metal. Raise the level gauge or take measures to prevent the level from rising too high. Improve the power supply by connecting it to ground or adding shielding. Change the installation location or insert a plastic tube. Use plastic flanges and rubber pads to isolate them from metal.