Differences and applications between ultrasonic level gauges and radar level gauges

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I. Differences in principle: The principle of ultrasonic level gauges. We generally refer to sound waves with frequencies exceeding 20 kHz as ultrasonic waves. Ultrasonic waves are a type of mechanical wave, that is, a form of propagation of mechanical vibrations through an elastic medium. Their characteristics include high frequency, short wavelength, minimal diffraction, as well as good directionality, allowing them to travel in a targeted manner as beams. Ultrasonic waves experience very little attenuation in liquids and solids, which gives them strong penetration capabilities; especially in opaque solids, ultrasonic waves can penetrate distances of several dozen meters. They are significantly reflected when they encounter impurities or interfaces, and it is this property that is utilized in ultrasonic level measurement. In ultrasonic testing technology, regardless of the type of ultrasonic instrument, electrical energy must be converted into ultrasonic waves for transmission, and then these waves must be received and converted back into electrical signals. The device that performs this function is called an ultrasonic transducer, also known as a probe. The ultrasonic transducer is placed above the liquid to be measured, and ultrasonic waves are emitted downward. These waves pass through the air medium and are reflected back when they encounter the water surface; they are then captured by the transducer and converted into electrical signals. The electronic detection unit detects these signals, converts them into level signals, and displays as well as outputs them. Based on the principle of ultrasonic wave propagation in a medium, if conditions such as medium pressure, temperature, density, and humidity remain constant, the speed at which ultrasonic waves propagate through that medium is a constant. Therefore, by measuring the time it takes for the ultrasonic wave to travel from emission to being received after reflecting off the liquid surface, the distance traveled by the ultrasonic wave can be calculated, thereby obtaining the liquid level data. Principle of radar level gauges: Radar level gauges operate on a transmit-reflect-receive principle. The antenna of the radar level gauge emits electromagnetic waves, which travel at the speed of light. After being reflected by the surface of the object being measured, these waves are then captured by the antenna. The time it takes for the electromagnetic waves to travel from transmission to reception is proportional to the distance from the radar to the liquid surface; the relationship is given by: D = CT/2, where D represents the distance from the radar level gauge to the liquid surface, C is the speed of light, and T is the time it takes for the electromagnetic waves to travel. The radar level gauge records the time taken by the pulse waves to travel, and since the speed of propagation of the electromagnetic waves is constant, it is possible to calculate the distance from the liquid surface to the radar antenna, thereby determining the liquid level. In practical use, radar level gauges come in two types: frequency-modulated continuous wave and pulse wave types. Level gauges that use frequency-modulated continuous wave technology consume a lot of power, require a four-wire system, and have complex electronic circuits. Level gauges that utilize radar pulse wave technology have low power consumption; they can be powered by 24VDC in a two-wire system, are easy to make intrinsically safe, offer high accuracy, and have a wider range of applications. Ultrasonic waves use sound waves, while radar uses electromagnetic waves; this is the biggest difference. Radar takes into account the dielectric constant of the material being measured ； Ultrasonic waves take into account the density of the material being measured. II. Differences in main application areas: Due to the different measurement principles of ultrasound and radar, their areas of application also differ. Radar relies on the dielectric constant of the material being measured, whereas ultrasound depends on the density of that material. Therefore, the radar measurement accuracy is reduced for materials with very low dielectric constants; ultrasonic waves are generally recommended for solid materials as well. Radar emits electromagnetic waves, which do not require a medium for propagation, whereas ultrasonic waves are sound waves, a type of mechanical wave that does require a medium for propagation. Furthermore, the components used for wave emission vary; for example, ultrasonic waves are generated through the vibration of piezoelectric materials, which means they cannot be used in environments with high pressure or negative pressure, and are generally only used in containers at normal pressure. And radar can be used in high-pressure process tanks. The transmission angle of radar is greater than that of ultrasonic waves; therefore, contactless radar is not recommended for small or narrow containers, with guided-wave radar being the preferred option in such cases. Finally, there is the issue of precision. Of course, the precision of radar is definitely higher than that of ultrasonic sensors; high-precision radar is used in storage tanks, rather than ultrasonic sensors. As for price, ultrasonic sensors are generally cheaper than radar sensors; of course, some ultrasonic sensors with a large range also come at high prices. The transmission of sound waves requires a medium, so they cannot propagate in a vacuum. Therefore, ultrasound has significant limitations in practical applications and falls short compared to radar. Firstly, ultrasonic level gauges have temperature limitations; generally, the temperature at the probe should not exceed 80 degrees, and the speed of sound is greatly affected by temperature. Secondly, ultrasonic level gauges are highly sensitive to pressure; generally, a pressure of less than 0.3 MPa is required, as sound waves are generated through vibration, and high pressure can affect the components responsible for producing sound. Third, accurate measurement cannot be achieved when there is a high level of fog or dust in the measurement environment. All of these factors limit the application of ultrasonic level gauges. In contrast, radar uses electromagnetic waves, which are not affected by the level of vacuum; it also has a wide range of applicability in terms of medium temperature and pressure. With the advent of high-frequency radars, its scope of application has become even broader. Therefore, radar is an excellent choice for level measurement. In summary, the differences between ultrasonic level gauges and radar level gauges are shown in the table below: Ultrasonic Level Gauge Radar Level Gauge Principle Distance = Speed * Time Distance = Speed * Time Transmitted waves Sound waves Electromagnetic waves Transmission angle Larger Smaller Requirements for medium Medium density Dielectric constant of the medium Accuracy Low High Range Small Large Temperature -40~80 degrees -40~300 degrees Pressure 0~0.3MPA -0.1~4MPA Measurement environment Can only propagate in clean air; no restrictions Price Low High