Views: 0 Author: Site Editor Publish Time: 2022-03-09 Origin: Site
As a common level instrument product, radar level meter is often used for level measurement of liquids, slurries and granular materials in various metal and non-metal containers or pipes. According to the working mode of radar level meter, there are two types of radar level meter: contact type and non-contact type. Compared with the contact radar level gauge, the non-contact radar level gauge is the fastest growing measuring instrument in recent years. factors, etc. According to the waveform of microwave, non-contact radar level meter can be divided into pulse radar level meter and FM continuous wave radar level meter. Contact radar level gauges mainly include guided wave radar level gauges. Let's talk about their principles and applications in combination with these common radar level gauges.
The guided wave radar emits high-frequency microwave pulses that propagate along the detection component (steel cable or steel pipe). The time interval between the transmitted pulse and the reflected pulse is proportional to the distance of the measured medium. The actual material level value can be calculated by the time of the transmitted pulse and the received pulse recorded by the radar level meter.
2. Pulse radar level meter
The pulse radar level meter transmits microwave pulses, and the pulses propagate at the speed of light (in the air). Depends on the flatness of the material surface/dielectric constant), received by the same antenna, the greater the amount of reflection (rate) of the medium, the stronger the signal, the better the measurement; the smaller the amount of reflection (rate), the weaker the signal, more easily disturbed. By accurately identifying the time interval Δt between the transmitted pulse and the received pulse, the distance D from the antenna to the surface of the measured medium can be further calculated.
3. FM continuous wave radar level meter
The FMCW radar uses 24GHZ as the measurement base frequency (carrier frequency), 2GHZ as the adjustment bandwidth, and the entire scan time is 7ms. After completing a linear scan, after the signal is transmitted, after a certain time delay, the echo signal is received. The time difference generated in the linear frequency sweep is proportional to the liquid level distance. Since there are many reflected waves, all the echo times are subjected to Fast Fourier (FFT) transformation to convert the time signal into a spectrum with a certain energy, which is relatively high and A relatively steep video spectrum signal is a useful signal.
Because the radar level meter has the advantages of accurate measurement, stable performance, high reliability, easy maintenance, and wide application range, its application range is very wide, covering power, steel, metallurgy, cement, petrochemical, paper, food and other industries. It is suitable for occasions where dust, temperature and pressure change greatly, and there are inert gases and steam. However, due to the different application principles of different radar level gauges, the application conditions it solves are also very different. The specific performance is as follows:
1. Pulse radar level meter can be generally used in most applications, usually used for liquid level measurement of medium in cylindrical tanks within 35 meters.
2. For spherical tanks or liquid storage tanks with stirring function, guided wave radar level gauges are usually used for liquid level measurement.
3. When measuring the medium of a container or storage tank with a large range and large dust, it is necessary to use a FM continuous wave radar level gauge with high energy and strong anti-interference ability, otherwise the measurement result may not be accurate enough.
Guided wave radar level gauges use the principle of time domain reflectometry (TDR) for measurement. Its working principle is: the electronic unit emits low-power, nanosecond-level electromagnetic wave pulses, which are transmitted through the probe (cable) immersed in the process medium. When it contacts the measured medium, a reflected signal is generated, which is received by the electronic components. According to the principle of travel time Calculate the interval time from transmission to reception and convert it into the distance of the measured medium. To put it simply, the working mode of the guided wave radar level gauge is emission-reflection-reception.
The guided wave radar level gauge has a flexible process connection form. In engineering, flanges or threads are generally used to install on the top of the equipment, and the probe (cable) is located vertically in the storage tank, and can also be installed in the equipment bypass pipe. The transmitter can be rotated 360° in the horizontal direction, which is convenient for cable connection and viewing of the meter display. According to the characteristics of the medium, choose a reasonable installation position to avoid affecting the measurement effect.
For the rigid-rod guided wave radar level gauge, the probe is inserted vertically into the liquid medium to stabilize the probe. If the probe is fluctuated by the medium during operation, it may move. The range is within 0.3m. fixed. There should be a gap between the probe and the bottom of the container, and the gap should be at least 5mm. The probe must not touch the nozzle of the equipment, and there must be enough installation space. For the flexible cable type guided wave radar level gauge, the wave guide rod must be in contact with the medium, and the guide wave cable must be stabilized to guide it to the bottom of the container and fixed with a heavy hammer or a bow clip. If the wall of the metal container is smooth, the minimum horizontal distance between the guided wave radar and the inner wall of the device is 100mm. If there is interference in the container, the minimum gap is larger, and the manufacturer's data shall prevail.
Guided wave radar level gauges can be used not only in vessels with narrow geometric dimensions, but also in bypass pipes and storage tanks of various sizes, making them ideal for horizontal tanks and other small storage tanks. Also ideal for underground storage tanks where installation space is limited.