Measurement Principle, Characteristics and Application of Radar Level Meter

Radar level meter is a non-contact liquid level measuring instrument with no moving parts and truly maintenance-free. After years of application and technical improvement, the instrument is currently widely used in the petrochemical industry and has been recognized by users. This article briefly introduces the two different measurement principles of radar level meter, and points out the suitable application occasions and installation requirements based on its characteristics and advantages.

1. Measurement principle and characteristics of radar level meter

Radar level meter uses ultra-high frequency electromagnetic waves to transmit to the liquid surface of the measured container through the antenna. When the electromagnetic wave reaches the liquid surface, it is reflected back and received by the same antenna. The time difference between the transmitted wave and the echo is detected, thereby calculating the liquid level.

Radar level meter has two working modes, corresponding to two measurement principles.

（1） Pulse microwave mode (PTOF)

This mode is a "top-down" time travel measurement system. The measurement system periodically transmits a fixed frequency microwave pulse through the antenna with a fixed bandwidth, which is received by the radar system after being reflected on the surface of the measured material. The antenna receives the reflected microwave pulse and transmits it to the electronic circuit. The microprocessor processes the signal, identifies the echo generated by the microwave pulse on the material surface, and calculates the liquid level based on it. The time proportional to the measured liquid level distance is converted into an electrical signal.

（2） Frequency Modulated Continuous Wave (FMCW)

The microwave source of this radar level meter is an x-band control oscillator. The microwave emitted by the antenna is a continuous wave with linear frequency modulation. When the echo is received by the antenna, the microwave emission frequency has changed. The frequency difference between the transmitted wave and the echo is proportional to the distance from the antenna to the liquid surface, and the liquid level height is calculated from this.

2. Characteristics of radar level meter

（1） The radar level meter is mainly composed of an electronic control unit and an antenna. There are no moving parts and no mechanical wear. Compared with the liquid level measuring instrument with mechanical parts, it has a longer service life. It is truly maintenance-free.

（2） The radar level meter can be used for the level measurement of most liquid levels. The microwaves it emits can pass through a vacuum, do not require a transmission medium, and are less affected by the atmosphere, steam, and volatile mist in the tank.

（3） Adopt non-contact measurement, which is not affected by physical properties such as liquid level density and concentration in the tank. It has a large measuring range and strong corrosion resistance.

（4） It has the advantages of easy installation, low failure rate, easy maintenance, high precision and high reliability.

（5） It adopts two output modes, digital and analog, and can be configured in bus mode for single or multiple units, which can be easily connected to the upper monitoring computer.

（6） The instrument has low radiation rate and basically does no harm to the surrounding environment and personnel.

3. Selection and application of radar level meter

There are many types of radar level meters. When selecting, the first thing to consider is the influence of the temperature, pressure, density, viscosity and corrosiveness of the measured medium on its performance. Therefore, when selecting, it is necessary to select suitable antennas and meters according to the characteristics of the medium under specific working conditions. For tanks with small volume and complex shape or applications where multiple liquid interfaces need to be measured, it is recommended to use a waveguide antenna radar level meter; for tanks with complex measurement environments, such as volatile, corrosive, high pressure and high temperature, it is recommended to use a non-contact antenna radar level meter. Since the level meter does not contact the medium, it can avoid the physical and chemical properties of the medium affecting its measurement accuracy or damage to the level meter itself.

Since the accuracy, daily maintenance and service life of the radar level meter directly affect the production efficiency and economic benefits of the enterprise, excellent quality and satisfactory after-sales service are crucial to users.

The selection principle is mainly considered from the following aspects, and the corresponding instrument selection specifications are followed:

(1) Instrument performance; (2) Medium characteristics; (3) Installation conditions; (4) Environmental conditions; (5) Economic factors.

The characteristics of the liquid level medium have a certain influence on the measurement range. Liquids with a smaller dielectric constant have a greater impact on the measurement distance of the radar level meter, which reduces the measurement range; liquids with a larger dielectric constant have a smaller impact on the measurement distance of the radar level meter, which increases the measurement range.

The performance of various types of radar level meters has its own characteristics. The appropriate model should be analyzed and determined according to the specific working conditions such as the use requirements, the temperature, pressure, corrosion characteristics of the measured medium and the size of the space used. For example, different antennas can meet various measurement requirements. The most commonly used cone antenna can be installed on the tank top or waveguide of the buffer tank and storage tank, which is suitable for measurement sites with a large measurement range, while the parabolic antenna is suitable for the measurement of liquid and solid phase levels and can be used for extremely long distance measurements. The small horn antenna is suitable for small containers, and the flat antenna is suitable for a variety of working conditions.

There are many types of liquid level measuring instruments, and each measurement method has its own characteristics and pertinence. Radar level meters can meet certain measurement requirements in liquid level measurement. Their working performance is stable and reliable, the operation is convenient and safe, the anti-interference ability is strong, and the measurable medium is large, which can achieve high measurement accuracy. Therefore, radar level meters will inevitably be widely used in the petrochemical industry with their characteristics and advantages.