The advantages and disadvantages of ultrasonic level gauges and radar level gauges
Ultrasonic uses sound waves, and radar uses electromagnetic waves. This is the biggest difference. Moreover, the penetration ability and directivity of ultrasonic waves are much stronger than electromagnetic waves, which is why ultrasonic detection is more popular now.
The difference between the main applications:
1. The radar measurement range is much larger than that of the ultrasonic.
2. The radar has a horn type, a rod type, and a cable type. Compared with ultrasonic, it can be applied to more complicated working conditions.
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. Ultrasonic cannot be applied to working conditions such as vacuum, high steam content or foam on the liquid surface.
We generally call sound waves with a sound wave frequency exceeding 20 kHz 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. In addition, It has good directivity and can become rays and propagate directionally. Ultrasonic attenuation is very small in liquids and solids, so it has 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. Ultrasonic measurement The level is to take advantage of this feature.
In ultrasonic testing technology, no matter what kind of ultrasonic instrument, it must convert the electric energy into ultrasonic and transmit it out, and then receive it back and transform it into an electrical signal. The device that completes this function is called an ultrasonic transducer, also called a probe. Place the ultrasonic transducer above the liquid to be measured, and emit ultrasonic waves downwards. The ultrasonic waves pass through the air medium and are reflected back when they meet the water surface. They are received by the transducer and converted into electrical signals, which are detected by the electronic detection part After this signal, it becomes 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 ultrasonic propagation speed in the medium is a constant. Therefore, when the time required for the ultrasonic wave to be received from the launch to the reflection on the liquid surface is measured, the distance that the ultrasonic wave passes through can be converted, that is, the liquid level data can be obtained.
Ultrasonic waves have blind spots, and the distance between the sensor installation position and the measured liquid must be calculated during installation.
The radar level gauge adopts a transmitting-reflecting-receiving working mode. The antenna of the radar level gauge emits electromagnetic waves. These waves are reflected by the surface of the object to be measured and then received by the antenna. The time from emission to reception of the electromagnetic wave is proportional to the distance to the liquid surface. The relationship is as follows:
D=CT/2
Where D——the distance from the radar level gauge to the liquid surface
C——the speed of light
T——the electromagnetic wave running time The
radar level gauge records the pulse wave elapsed time, and the transmission speed of the electromagnetic wave is constant, then the liquid level to the radar can be calculated The distance of the antenna, so as to know the liquid level of the liquid surface.
In actual application, there are two methods for radar level gauges: frequency modulated continuous wave type and pulse wave type. The level gauge using FM continuous wave technology has high power consumption, 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 a two-wire 24V DC power supply, which is easy to achieve intrinsic safety, high accuracy, and a wider range of applications.