The radar level gauge is now an indispensable detection instrument in the liquid level measurement industry. Because radar level gauge has more advantages than similar contact and non-contact level gauges, widely used in various industries. Its own advantages and measurement effects have gradually been recognized by more and more users. The following is the introduction to measuring principle and precautions of radar level gauge.
The radar level gauge adopts the working mode: transmitting - reflecting - receiving. 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 (D: the distance from the radar level gauge to the liquid surface; C: the speed of light; T: the operating time of electromagnetic waves)
The radar level gauge records the elapsed time of the pulse wave, and the transmission speed of the electromagnetic wave is constant, and the distance from the liquid surface to the radar antenna can be calculated, 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 and needs to 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 two-wire 24VDC, which is easy to achieve intrinsic safety and has a wider application range.
The antenna system of radar level gauge using pulsed microwave technology emits pulse beams with frequencies of 6.3GHz, 26GHz, 80GHz, and 120GHz. During the pause of pulse transmission, the antenna system will act as a receiver to receive the reflected wave. At the same time, the echo image data is processed, and instructions and electrical signals are given.
The radar level gauge adopts an integrated design, no moving parts, no mechanical wear, and has long service life. The electromagnetic wave emitted during the measurement can pass through the vacuum without a transmission medium. It has the characteristics of not being affected by the atmosphere, steam, and volatilized fog in the tank. It can be used for level measurement of volatilized media such as crude benzene. It can be used for level measurement of almost all liquids.
When the electromagnetic wave is reflected on the surface of the liquid level, the signal will attenuate. When the signal attenuation is too small, the radar level gauge will not be able to detect enough electromagnetic wave signals. Conductive media can reflect electromagnetic waves very well, and can reflect enough electromagnetic waves for radar level gauges and even slightly conductive materials. The dielectric constant greater than 1.5 (the dielectric constant of air is 1.0) can also ensure sufficient reflected waves. The larger the dielectric constant, the stronger the reflected signal.
Whether the radar level gauge can measure correctly depends on the signal of the reflected wave. If at the selected installation position, the liquid level cannot reflect electromagnetic waves back to the radar antenna or there are interference objects within the range of the signal wave to reflect interference waves to the radar level gauge, the radar level gauge cannot correctly reflect the actual liquid level. Therefore, a reasonable selection of the installation location is very important for the radar level gauge. The following points should be paid attention to when installing:
1. The axis of the radar level gauge antenna should be perpendicular to the reflective surface of the liquid level.
2. If the stirring valve in the tank, the adhesion of the tank wall and the steps, etc., are within the signal range of the radar level gauge, they will produce interference reflection waves, which will affect the liquid level measurement. When installing, choose a suitable installation location to avoid interference from these factors.
3. The horn of the horn-shaped radar level gauge should be installed at a distance of 1/2R from the center (R is the radius of the container) for a round or oval container, and cannot be installed in a round or elliptical container. Otherwise, after multiple reflections of the radar wave on the container wall, it will converge at the center of the container top, forming a strong interference wave, which will affect the accurate measurement.
4. For liquid level measurement of containers with large liquid level fluctuations, a radar level gauge with a bypass pipe can be used to reduce the impact of liquid level fluctuations.
The radar level gauge is mainly composed of electronic components and antennas. There are no moving parts and few faults in use. The occasional problem encountered in use is that some volatile organic matter in the storage tank will crystallize on the horn or antenna of the radar level gauge. As for this, regularly check and clean are require.