Radar level gauge adopts transmitting-reflecting-receiving mode. The antenna of the radar level gauge emits electromagnetic waves, which are reflected by the surface of the measured object and then received by the antenna. The time of electromagnetic wave from transmission to reception is proportional to the distance to the liquid surface. The relationship is as follows:
Distance from d-Radar Level Meter to Liquid Level
C - Speed of Light
T-Running Time of Electromagnetic Wave
Radar level gauge records the time of pulse wave, while the transmission speed of electromagnetic wave is constant, the distance between liquid surface and radar antenna can be calculated, so that the liquid level of liquid surface can be known.
In practical application, radar level gauge has two modes: frequency modulation continuous wave and pulse wave. The liquid level meter using FMCW technology consumes a lot of power. It must adopt four-wire system and its electronic circuit is complex. The liquid level meter using radar pulse wave technology has low power consumption and can be powered by two-wire 24vdc. It is easy to realize intrinsic safety, high accuracy and wide application range.
Ultrasound uses sound waves, radar uses electromagnetic waves, which is the biggest difference. Moreover, the penetration and directivity of ultrasound are much stronger than that of electromagnetic wave, which is the reason why ultrasonic detection is more popular nowadays.
Differences in main application occasions:
1. Ultrasound is not as accurate as radar.
2. The relative price of radar is higher.
3. When using radar, the dielectric constant of medium should be considered.
4. ultrasound can not be applied to vacuum, high steam content or liquid foam.
5. The range of radar measurement is much larger than that of ultrasound.
6. Radar has horn type, pole type and cable type. Compared with ultrasonic wave, it can be used in more complex working conditions.
Ultrasound is a kind of mechanical wave, that is, a propagation process of mechanical vibration in elastic medium. Its characteristics are high frequency, short wavelength, small diffraction phenomenon, good direction, and can be directed to radiation. Ultrasound attenuates very little in liquids and solids, so it has strong penetration ability. Especially in opaque solids, it can penetrate tens of meters in length. When it comes to impurities or interfaces, it will have a significant reflection. Ultrasound measurement of material level is based on this characteristic.
In the ultrasonic detection technology, no matter what kind of ultrasonic instrument, it is necessary to transmit electric energy into ultrasonic wave, and then receive back into electrical signal. The device to complete this function is called ultrasonic transducer, also known as probe. As shown in the figure, the ultrasonic transducer is placed above the measured liquid and emits ultrasonic wave downward. The ultrasonic wave passes through the air medium and is reflected back when it encounters the water surface. It is received by the transducer and converted into an electrical signal. The electronic detection part detects the signal and then displays it as a liquid level signal and outputs it.
According to the principle of ultrasonic propagation in medium, if the medium pressure, temperature, density, humidity and other conditions are certain, then the propagation speed of ultrasound in the medium is a constant. Therefore, when the time needed for the ultrasonic wave to be received from the launch to the encounter of the liquid surface reflection is measured, the distance through which the ultrasonic wave passes can be converted, that is, the data of the liquid level can be obtained.
Ultrasound has blind area. When installing, the distance between the sensor installation position and the measured liquid must be calculated.