The radar in the level meter (Radar Level Meter) is the abbreviation of the English Radio Detection and Raging (radio detection and ranging). Because it emits microwaves to the measured target to calculate the level distance, it is also called a microwave level meter. The ultrasonic level meter is a non-contact measuring instrument like the radar level meter, but it calculates the level distance by transmitting ultrasonic pulses to the measured target. It is a microprocessor-controlled digital level meter. Are there any differences between ultrasonic level gauges and radar level gauges? Of course, let's start with electromagnetic waves.

The band of electromagnetic waves is generally in the range of 3kHz~3000GHz, and the band is relatively wide, while microwaves refer to electromagnetic waves with frequencies of 300MHz~300CHz. In level measurement instruments, the frequency bands used by microwaves are approximately between 4 and 30 GHz. Among them, the frequencies of 5.8 GHz, 10 GHz, 24 GHz and 5.8 GHz belong to C-band microwave; the frequency of 10 GHz belongs to X-band microwave; the frequency of 24 GHz belongs to K-band microwave.

Unlike electromagnetic waves, sound waves are mechanical waves with a frequency range between 20Hz and 20kHz. If the vibration frequency of sound waves is higher than 20kHz or lower than 20kHz, it is in a category that cannot be recognized by the human ear. Therefore, sound waves with frequencies higher than 20kHz are called "ultrasonic waves".

Electromagnetic waves and sound waves not only have different frequencies, but also different principles. For sound waves, their generation must rely on material vibration and cannot propagate in a vacuum; electromagnetic waves are generated by the oscillation of electrons. Since they are matter themselves, they do not require a medium for propagation and can propagate in a vacuum. What electromagnetic waves and sound waves have in common is that when they encounter different media, phenomena such as refraction, reflection, diffraction, scattering, and absorption will occur. Ultrasonic liquid level meters and radar level meters use this phenomenon to measure the level distance.

The working theory of ultrasonic level gauge actually originates from sonar technology. Earlier ultrasonic level gauges used liquid sound conduction to install the ultrasonic transducer, that is, the probe, at the bottom of the tank, so that ultrasonic waves are emitted from the bottom, propagate through the liquid medium to the liquid surface, and are then reflected back to the transducer. Although this measurement method of installing an ultrasonic liquid level meter at the bottom of the tank is feasible, its practicability is very low. Because the propagation speed of ultrasonic waves in different measured media is also different, the measurement data will inevitably have deviations; and the method of installing a probe at the bottom of the tank is also very difficult to install. Therefore, humans realized the convenience of using air as the sound-conducting medium for ultrasonic liquid level meters, and began to gradually install them on the top of the tank, which greatly improved its work efficiency.

The sound wave signal of the ultrasonic level gauge is reflected on the interface with different acoustic resistance rates (acoustic resistance rate = material density x sound speed). Due to the different densities of air and materials, their acoustic resistance rates are also different. However, since ultrasonic waves are mechanical waves, their wavelength is less than 17mm when propagating in the air, and the propagation speed is affected by temperature (for example, when the temperature is 0°C, the speed of sound is 331.6m/s; when the temperature is 20°C, the speed of sound is 344m/s). Therefore, in order for an ultrasonic liquid level meter to become a mature product with a wide range of applications, it must have temperature compensation technology.

Jiwei Uson-11 ultrasonic liquid level gauge is an economical liquid level measuring instrument equipped with internationally advanced temperature compensation technology, and uses microprocessor program control and intelligent signal processing technology as well as special echo processing methods to effectively avoid false echoes. In addition, the protection level of the whole machine is as high as IP66, and the measurement results are accurate and reliable.

Compared with ultrasonic level gauges, the microwave signals of radar level gauges are reflected on interfaces with different dielectric constants. The dielectric constant is a coefficient that represents the insulation capability characteristics, generally expressed as ε, and changes with temperature and the frequency of electromagnetic waves propagating in the medium. Generally, the larger the dielectric constant, the stronger the ability to bind charges; the smaller the dielectric constant, the better the insulation.

The microwave signal of the radar level meter propagates at the speed of light, and the speed is almost unaffected by the characteristics of the medium, and the propagation attenuation is also very small, about 0.2dB/km. However, the strength of the echo signal is closely related to the reflection of the measured liquid surface. It can be said that the reflectivity on the measured liquid surface is not only related to the area and shape of the measured material, but also mainly depends on the relative dielectric constant (εr) of the material. If the relative dielectric constant is high, the reflectivity is also high and the echo obtained is strong; if the relative dielectric constant is low, the material will absorb part of the microwave energy and the echo will be weak. The relative dielectric constant εr of most radar liquid level measured materials on the market today is >4, but for materials with low dielectric constants, it is necessary to add a waveguide to enhance the echo signal, or you can only use a high-end radar with a lower measurement limit of εr>2.