Views: 8 Author: Site Editor Publish Time: 2022-04-04 Origin: Site
The ultrasonic level gauge ses sound waves, and the radar level gauge uses electromagnetic waves, which is the biggest difference. Moreover, the penetrating ability and directionality of ultrasonic waves are much stronger than that of electromagnetic waves, which is why ultrasonic detection is more popular now.
1. The measuring range of radar is much larger than that of ultrasonic.
2. Radar has horn type, rod type and cable type, which can be applied to more complex working conditions than ultrasonic.
3. Ultrasonic accuracy is not as good as radar.
4. The relative price of radar is relatively 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.
We generally refer to sound waves with a frequency of more than 20 kHz as ultrasonic waves. Ultrasound is the first type of mechanical wave, that is, the first propagation process of mechanical vibration in an elastic medium. It is characterized by high frequency, short wavelength, and small diffraction phenomenon. In addition, it has good directivity and can be directed to propagate as a ray. Ultrasonic waves have very little attenuation in liquids and solids, so they have strong penetrating ability, especially in solids that are opaque to light, ultrasonic waves can penetrate a length of tens of meters, and there will be significant reflections when they encounter impurities or interfaces. The material level is to use this characteristic of it.
In ultrasonic testing technology, no matter what kind of ultrasonic instrument, it must convert electric energy into ultrasonic waves and transmit them, 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. As shown in the figure, the ultrasonic transducer is placed above the liquid to be measured, and the ultrasonic wave is emitted downward. The ultrasonic wave passes through the air medium, is reflected back when it encounters the water surface, and is received by the transducer and converted into an electrical signal. The electronic detection part detects this * signal and turns it 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 fixed, the propagation speed of ultrasonic waves in the medium is the first constant. Therefore, when the time required for the ultrasonic wave to be received from the time it is transmitted to the time it encounters the liquid surface reflection is measured, the distance the ultrasonic wave passes through can be converted, that is, the data of the liquid level is obtained.
Ultrasonic has a blind area, and the distance between the installation position of the sensor and the measuring liquid must be calculated during installation.
The radar level gauge adopts the working mode of transmitting-reflecting-receiving. The antenna of the radar level gauge emits electromagnetic waves. 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:
where D is the distance from the radar level gauge to the liquid level
C - the speed of light
T——Electromagnetic wave running time
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 level to the radar antenna can be calculated, so as to know the liquid level of the liquid level.
In practical applications, there are two types of radar level gauges, namely, the frequency-modulated continuous wave type and the pulse wave type. The liquid level gauge using frequency modulation continuous wave technology has high power consumption, must use a four-wire system, and the electronic circuit is complex. The liquid level gauge 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 wider application range.