Ultrasonic Level Sensor VS. Radar Level Sensor

The difference in working principle:

We generally refer to sound waves with a sound wave frequency exceeding 20kHz as ultrasonic waves. Ultrasonic waves are a type of mechanical wave, that is, a propagation process of mechanical vibration in elastic media. It is characterized by high frequency, short wavelength, and small diffraction phenomena. Good directionality can become ray and directional propagation. The attenuation of ultrasonic waves in liquids and solids is very small, so the penetrating ability is strong, especially in solids that are opaque to light, ultrasonic waves can penetrate tens of meters in length, and there will be a significant reflection when encountering impurities or interfaces. The ultrasonic level meter measures the material level with this principle.

In ultrasonic testing technology, no matter what kind of ultrasonic equipment, it is necessary to convert electrical energy into ultrasonic waves, and then receive them back and convert them into electrical signals. The device that completes this function is called an ultrasonic transducer, also known as a probe. Place the ultrasonic transducer above the liquid to be tested and emit ultrasonic waves downward. The ultrasonic waves pass through the air medium and are reflected back when they meet the water's surface. They are received by the transducer and converted into electrical signals, which are detected by the electronic detection part. This signal is then turned into a liquid level signal for display and output.

According to the principle of ultrasonic propagation in the medium, if the medium pressure, temperature, density, humidity, and other conditions are constant, the propagation speed of ultrasonic waves in the medium is constant. Therefore, when the time required for the ultrasonic wave to be reflected from the liquid surface to be received is measured, the distance traveled by the ultrasonic wave can be converted, that is, the liquid level data can be obtained.

Ultrasonics have a blind area, and the distance between the sensor installation position and the measurement liquid must be calculated during installation.

The radar level sensor adopts the working mode of transmission-reflection-reception. The antenna of the radar level sensor emits electromagnetic waves, and the radar waves travel at the speed of light. These waves are reflected by the surface of the measured object and then received by the antenna. The time from emission to reception of electromagnetic waves is proportional to the distance to the liquid surface. The relationship is as follows:

D=CT/2

In the formula, D -- the distance from the radar level sensor to the liquid surface

C -- the speed of light

T -- electromagnetic wave running time

The radar level sensor records the elapsed time of the pulse wave, and the transmission speed of the electromagnetic wave is constant, so the distance from the liquid surface to the radar antenna can be calculated, so as to know the liquid level of the liquid surface.

In practice, there are two types of radar level sensors, FM continuous wave and pulse wave. The liquid level sensor using frequency modulation continuous wave technology consumes a lot of power, must use a four-wire system, and has complex electronic circuits. The liquid level sensor using radar pulse wave technology has low power consumption and can be powered by two-wire 24V DC, which is easy to achieve intrinsic safety, high accuracy, and a wider application range.

Ultrasound uses sound waves, while radar uses electromagnetic waves. This is the biggest difference. Moreover, the penetration and directionality of ultrasonic waves are much stronger than electromagnetic waves, which is why ultrasonic detection is more popular now.

The difference between the main application occasions:

Ultrasonic level sensors and radar level sensors are mainly different in measurement principles, which leads to their different application occasions. The radar level sensor is based on the dielectric constant of the measured substance, while the ultrasonic level sensor is based on the density of the measured substance. Therefore, the measurement effect of the radar for substances with a very low dielectric constant will be compromised. For solid substances, ultrasonic level sensors are generally recommended. 

At the same time, the radar level sensor emits electromagnetic waves and does not need a medium for transmission, while the ultrasonic level sensor emits sound waves, which are a kind of mechanical wave and require a medium for transmission. In addition, the components of the wave emission method are different. For example, the ultrasonic liquid level sensor is emitted by the vibration of the piezoelectric material, so it cannot be used in high-pressure or negative-pressure occasions and is generally only used in normal pressure vessels. The radar level sensor can be used in high-pressure process tanks. 

The emission angle of the radar level sensor is larger than that of the ultrasonic wave. It is not recommended to use non-contact radar in small or slender containers. Generally, guided wave radar level sensors are recommended. Finally, there is the issue of accuracy. Of course, the accuracy of radar level sensors must be higher than that of ultrasonic level sensors. High-precision radar level sensors must be used on storage tanks instead of ultrasonic level sensors. As for the price, the ultrasonic level sensor is generally lower than the radar level sensor. Of course, the price of some large-range ultrasonic level sensors is also very high, such as the range of 6 to 70 meters. At this time, the radar level sensor cannot reach arrived, only the ultrasonic liquid level sensor can be selected!

The transmission of sound waves needs a medium, so it cannot propagate in a vacuum. Therefore, the limitations of ultrasonic liquid level sensors in practical applications are still very large, and there are many deficiencies compared with radar liquid level sensors. First of all, the ultrasonic level sensor has a temperature limit. Generally, the temperature at the probe cannot exceed 80 degrees, and the speed of sound waves is greatly affected by the temperature. Secondly, the ultrasonic level sensor is greatly affected by the pressure, generally within 0.3MPa, because the sound waves are emitted by vibration and the sound-generating parts will be affected when the pressure is too high. Third, it will not be able to measure well when there is a lot of fog or dust in the measurement environment. 

All of these limit the application of ultrasonic level sensors. In contrast, the electromagnetic wave of the radar level sensor is not affected by the vacuum degree and has a wide range of applications the medium temperature and pressure. With the emergence of high-frequency radar, its application range is even wider. Therefore, in level measurement among them, the radar level sensor is a good choice.

However, whether it is a radar level sensor or an ultrasonic level sensor, attention must be paid to the installation position and blind spots during the installation process. For example, when it is installed on the tank, it should not be installed at the feed inlet or near the ladder, and it should be 300 to 500mm away from the tank wall to prevent echo interference. When there is stirring and the liquid level fluctuates greatly, it is also necessary to choose a suitable installation method.

Summary:

1. The measurement range of the radar level sensor is much larger than that of the ultrasonic level sensor.

3. Ultrasonic liquid level sensor is not as accurate as radar.

4. The relative price of the radar level sensor is relatively high.

5. When using a radar level sensor, the dielectric constant of the medium should be considered.

6. Ultrasonic level sensors cannot be used in working conditions such as vacuum, high steam content, or foam on a liquid surface.

In summary, the choice between an ultrasonic level sensor and a radar level sensor depends on the specific application and the properties of the liquid or solid being measured. Ultrasonic sensors are generally better suited for measuring the level of liquids, while radar sensors are better suited for measuring the level of solids and can cover longer distances.