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Level sensor detection method - microwave, ultrasonic, radar

- Jun 29, 2018 -

Microwave sensors, ultrasonic sensors, and radar sensors have a wide range of applications for liquid level detection, and their features are that they do not require direct contact with the product to achieve its purpose. Each of these technologies has the ability to bypass some of the internal obstacles, but each has its own limitations.

Microwave sensor

Microwave sensors (radar sensors) use electromagnetic energy, rather than air molecules, so they penetrate the temperature and vapor layers and can be used in a vacuum. Objects where electromagnetic energy is reflected, such as metal and conductive water, have high electrical conductivity.

There are two basic processing techniques: Time-Domain Reflectometry (TDR) is a measure of the speed of flight divided by the speed of light; FMCW (Frequency Modulated Continuous Wave) technology can be found in the Doppler system. Microwave sensors use non-contact technology that can be performed at different frequencies. They are high-frequency, more accurate, and expensive sensors.


Ultrasonic and radar technologies have a wide range of applications, characterized by the fact that they do not require direct contact with the product. Of course, they do need an access point at the top of the tank (except for the measurement points through the wall).

Ultrasonic sensor

The ultrasonic sensor emits high-frequency sound waves that are reflected back to the transmitting transducer. After the sonic pulse is sent into the tank, the sensor checks the echo return time. Integrating the humidity and temperature factors, it can calculate the distance to the surface. Ultrasonic measurements are affected by turbulence, foam, vapor, and changes in concentration. Ultrasonic sensors can be used for continuous point detection with low cost and high performance.


Another type of ultrasonic sensor can be mounted on the wall of the container and can take a level contact without penetrating. Sonic pulse and echo can determine if there is solid or liquid material on the other side of the container wall. In some cases, it can even distinguish between what is above the liquid level and only a layer of material that sticks to the wall. This method is particularly suitable for applications where capacitive measurements cannot be used, contact with the object to be measured is not possible, and the can body is not perforated.

Radar sensor

Radar—This technology has been used in the field for more than 25 years, but in recent years, as its performance has improved and its cost has decreased, the use of radar technology has increased. In the past, the expensive price, huge size and high energy consumption have made radar sensors only used in places where they have to be used, but now they are more widely available. Radar is similar to ultrasound, but less restrictive and generally more accurate: Microwave pulses can better understand foam and dust, and are less limited by pressure and temperature.

Radar sensors can be equipped with non-contact probes or waveguides that extend into the interior of the medium. Non-contact design is more common, but when the dielectric constant of the liquid is very low and the microwave signal cannot be well reflected, the guided wave method will become practical. The probe of the guided wave device transfers the energy into the liquid and obtains its feedback. If there is no problem with the product contact, the strength of the returned signal will be much higher. The

Radar sensors have a variety of antenna configurations to meet the special requirements of your internal space and liquid properties for optimal results. In addition, different frequencies can provide various targeted functions for various difficult conditions and liquid properties.

Application area

Microwave sensors are suitable for humid, vaporized and dusty environments and can also be used to detect temperature changes in the system.

Radar sensors are particularly suitable for environments with high internal pressure, high temperatures, fog, steam, rapids, and other issues. The biggest problem at the moment is the bubble. It is necessary to understand the dielectric constant of the liquid, the size or density of the foam, and how thick the foam layer is. It is recommended that the wave guide device be capable of filtering the interference of a thick foam layer.

Compared with radar, the application of ultrasonic temperature and pressure range is relatively more limited. Ultrasonic liquid level sensors are used in non-contact applications with highly viscous solid bulk materials, including remote control/wireless monitoring and factory network communication systems.

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