Radar level gauge is a commonly used product type of level gauge. It has the advantages of accurate measurement, stable performance, high reliability, easy maintenance and wide application range. It can be installed in various metal and non-metal containers or pipes to measure the level of liquid, slurry and granular materials.
It is suitable for occasions with large changes in dust, temperature and pressure, and the presence of inert gas and steam. So, what are the types and applications of radar level gauges?
Radar level gauges can be divided into contact radar level gauges and non-contact radar level gauges according to working methods, as follows:Non-contact (radio-air radar) radar level gauge
Non-contact radar level gauges usually use horns or rod antennas to transmit and receive microwaves. The instrument is installed on the top of the silo without contact with the measured medium. Microwaves propagate and return in the upper space of the silo.
Non-contact radar level gauges can be divided into pulse radar level gauges and frequency-modulated continuous wave radar level gauges according to the microwave waveform.
Contact radar level gauge
Contact radar level gauges generally use metal wave conductors (rods or steel cables) to conduct microwaves. The instrument is installed from the top of the warehouse, and the guided waves reach the bottom of the warehouse. The reflection is returned to the transmitter along the wave guide and received.
This kind of contact radar level meter, which can be measured by directly touching the measured material through the guide line or the probe, is mainly a guided wave radar level meter. It can be further subdivided into : Cable type (single / double), rod type (single / double) and coaxial guided wave radar level gauge.
Compared with contact radar level gauges, non-contact radar level gauges have the advantages of simple installation, less maintenance, flexible usage, and are not affected by factors such as dust and temperature in the warehouse. Kinds of measuring instruments.
Second, the technical principle
Pulse radar level meter
The pulse radar level gauge will emit microwave pulses, propagate at the speed of light (in the air), and hit the surface of the measured medium (the dielectric constant must be greater than the dielectric constant of the propagation medium), and some microwaves are reflected back (the amount of reflection depends on the material Flatness / dielectric constant), received by the same antenna, the greater the reflection amount (rate) of the medium, the stronger the signal, the better the measurement; the smaller the reflection amount (rate), the weaker the signal, the more susceptible interference. Accurately identify the time interval Δt between the transmitted pulse and the received pulse, so as to further calculate the distance D between the antenna and the surface of the measured medium.
FM continuous wave radar level meter
FMCW radar uses 24GHZ as the measurement base frequency (carrier frequency), 2GHZ is the adjustment bandwidth, the entire scanning time is 7ms, completes 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 will be proportional to the liquid level distance.
Due to the 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, and the video spectrum is relatively high And the steeper signal is the useful signal.
Guided wave radar level gauge
Guided wave radar sends high-frequency microwave pulses to propagate along the detection component (steel cable or steel pipe). When encountering the measured medium, due to the sudden change in dielectric constant, it causes emission, and part of the pulse energy is emitted back. The time interval between the transmitted pulse and the reflected pulse is proportional to the distance of the measured medium.
Third, the application difference
Radar level gauges have a wide range of applications, covering fields such as electricity, steel, metallurgy, cement, petrochemicals, papermaking, and food. However, radar level gauges with different principles have different application conditions.
Pulse radar level gauges can generally be used in most applications, mainly for the liquid level measurement of the cylindrical medium within 35 meters; however, for spherical tanks or liquid storage tanks with stirring function, guided wave radar Level meters are used for measurement; however, for large-scale, dusty containers or storage tanks, frequency-modulated continuous wave radar level meters with large energy and strong anti-interference capabilities must be used.
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