频率超过20kHz的声波称为超声波，超声波是机械波的一种，即是机械振动在弹性介质中的一种传播过程，它的特征是频率高、波长短、绕射现象小，另外方向性好，能够成为射线而定向传播。 We generally call sound waves with an ultrasonic flowmeter with a frequency exceeding 20kHz as ultrasonic waves. Ultrasonic waves are a type of mechanical waves, that is, a process of mechanical vibration propagation in elastic media. It is characterized by high frequency, short wavelength, and small diffraction In addition, it has good directivity and can become ray and directional propagation. Ultrasonic waves have very low attenuation in liquids and solids, and therefore have strong penetrability. Especially in solids that are opaque to light, ultrasonic waves can penetrate tens of meters in length, and there will be significant reflection when they encounter impurities or interfaces. Ultrasonic measurement Level is the use of this feature. In the ultrasonic detection technology, no matter what kind of ultrasonic instrument, it is necessary to transmit the electric energy converted ultrasonic wave, and then receive it back and convert it into electrical signals. The device that accomplishes this function is called an ultrasonic transducer, also called a probe. As shown in the figure, the ultrasonic transducer is placed above the liquid to be measured, and the ultrasonic wave is transmitted downward. The ultrasonic wave passes through the air medium and is reflected back when it encounters the water surface. The electronic detection part detects this signal and turns it into a liquid level signal for display and output. From the principle of ultrasonic wave propagation in a medium, it can be known that if the medium pressure, temperature, density, humidity and other conditions are constant, the propagation speed of the ultrasonic wave in the medium is a constant. Therefore, when the time required for the ultrasonic wave to be received from the reflection of the liquid surface is measured, the distance through which the ultrasonic wave passes can be converted, and the liquid level data is obtained. Ultrasound has blind spots. The distance between the sensor installation position and the measurement liquid must be calculated during installation.
The radar level gauge records the time elapsed by the pulse wave, and the transmission speed of the electromagnetic wave is constant, 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 practical applications, there are two methods for radar level gauges, namely FM continuous wave and pulse wave. The liquid level gauge using FM continuous wave technology has large power consumption, and must adopt a four-wire system, and the electronic circuit is complicated. The level gauge using radar pulse wave technology has low power consumption and can be powered by two-wire 24V DC. It is easy to achieve intrinsic safety, high accuracy, and a wider range of applications. The biggest difference is the use of sound waves for ultrasound and electromagnetic waves for radar. 的穿透能力和方向性都比电磁波强的多，这就是超声波探测现在比较流行的原因。 And the penetrability and directivity of ultrasonic flowmeters are much stronger than electromagnetic waves, which is why ultrasonic detection is now more popular. Differences in main applications: 1. Radar measurement range is much larger than ultrasonic. 2. Radar has horn type, rod type and cable type. Relative ultrasonic waves can be applied to more complicated working conditions. 3. Ultrasonic accuracy is not as good as radar. 4. The relative price of radar is high. 5. When using radar, consider the dielectric constant of the medium. 6. Ultrasound cannot be used in vacuum, high steam content or foam on the liquid surface.
应用： Application of ultrasonic level gauge :
1.Measure flow, liquid level, low gauge pressure, vacuum and specific gravity
2.The maximum range of two-wire system can reach 30m
3.The maximum range of the four-wire system can reach 40m
4.Minimum resolution 1mm
5. Large LCD / LED display
6.Intelligent signal processing technology
7. Equipped with high and low double relays (only four-wire system)
8. All-plastic anticorrosive shell (protection level lP67)
9. Patented transducer structure (when the flange of the small-range level gauge is installed, there is no requirement for the length of the flange connection)
10. Simple button setting parameters (no need to wait for the container to empty or fill up, no additional remote control required)
11. Flexible installation method (thread / flange, fixing hole / bracket)
12. AC or DC power supply is optional (only four-wire system)