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Focus On Level Measurement
Ow To Achieve The Best Performance Of Radar Level Meter?(On)
Radar frequency, antenna design, intelligent algorithm and installation location all play an important role in the successful measurement of material level in tank or silo.The more complex and precise the application, the more critical it is to obtain the optimal frequency and antenna design.
For material level measurement, the free space radar transmitter usually USES 6, 26 and 80GHz frequencies.Recently, there has been a lot of hype about high-frequency radar transmitters, with some companies claiming that the higher the frequency, the better the performance.Well, that's not necessarily true.Instead, accuracy depends on frequency, beam Angle, antenna configuration and installation, but the most important is the product's dielectric constant.
The free space radar transmitter operates on two main principles: time of flight (TOF) and frequency modulated continuous wave (FMCW).Each USES "time" as the basis for distance measurements, but the way they are calculated varies.
The TOF radar USES microwave pulses from a transmitter.When microwave energy reaches the measured object, the impedance changes due to the change of dielectric constant (gas phase, liquid or solid surface), and the microwave energy is reflected.The reflected energy depends on the dielectric constant of the material being measured.Highly dielectric materials, such as water, reflect all or most of the energy.Low dielectric materials, such as hydrocarbons, reflect less energy.
Microwaves move at the speed of light, and radar measures the time it takes for a pulse of microwaves to reach the surface and return.Divide the time by two to get the distance scale.The transmitter subtracts the distance measurement from the measuring range to obtain the material level in the storage tank or silo.
FM continuous wave (FMCW) radar also aims microwave energy at the surface of the material under test.Like TOF radar, the reflected energy depends on the dielectric constant of the material.FM continuous wave radars transmit a continuous flow of energy rather than pulses, and the frequency is continuously modulated or varied.Therefore, for an 80 GHz FMCW radar, the transmitter frequency may start at 79GHz and gradually rise to 81GHz.
The transmitter compares the frequencies reflected from the material surface with those sent out.The difference in frequency equals the time it takes for the microwave to reach the surface and return.Just like TOF radar, the distance measurement is subtracted from the measuring range to get the applied material level.
While manufacturers cite a variety of reasons why one technology is better than another, it's important to consider the specifics of each application.Both technologies use microwave energy to travel at the speed of light, and the reflection of that energy depends on the dielectric constant of the material being measured, so both methods measure time to determine distance or material level.
Many factors affect the accuracy and availability of measurement signals, including frequency, antenna type, installation conditions and dielectric constant of the material under test.
Figure 1: this figure compares the sharp peak of a 26 GHz radar emitter with the rounded peak of a 6 GHz radar reflector in the same application.
Transmitter frequency affects accuracy, beam Angle and antenna size.Compared with higher frequency transmitters, low frequency transmitters are generally less accurate because the signal resolution produced by lower frequency transmitters is poor.Figure 1 shows a comparison of the envelope curves between the 6 GHz and 26 GHz radar emitters.The pulse produced by the 26 GHz radar (red line) is about half the length of the 6 GHz pulse (blue line).This provides more accurate reflection and higher accuracy.
The 6 GHz pulse is much wider than the 26 GHz pulse.The transmitter decodes the pulse and determines the position of the material level.The blue arrow indicates that you can decode at multiple points.The transmitter can decode the leading edge, center or lower edge into the feed level, which affects the accuracy.Since the 26GHz emitter pulse is sharper, this limits the decoding to a single point, as shown by the red arrow.The result is that, in process applications, 6 GHz emitters typically have an accuracy of 6 to 10 mm, while 26 GHz emitters can provide an accuracy of 2 to 3 mm.
Advanced algorithms can be applied to tank measurements with accuracy less than 1 mm.The 80 GHz radar also reflects sharp peaks, making it relatively easy to accurately measure the material level.Using the 80GHz process radar, the measurement accuracy in the application can reach 1 mm, while using the 80GHz tank measurement and managed transmission radar accuracy is less than 0.5 mm.
Frequency also affects the beam Angle of the transmitter signal.Transmitters with lower frequencies generate wider beam angles than those with higher frequencies.In some applications, wide beam angles may be more suitable than narrow beam angles.