What Radar Level Measurement Systems are There

Most radar systems are utilized for the purpose of detecting the height of liquids in continuous level measurement systems. If you're measuring liquid levels in a metal tank, a non-contact kind of level measurement (radar level transmitters) is a better option. They make use of EM, which is commonly defined as electromagnetic waves in the microwave X-band spectrum that is between around 10 GHz and a few GHz. Due to this, they can also be referred to as microwave-level measurement devices like VEGAPULS 64. On the other hand, radar and microwave systems differ in a few ways. They are as follows:

All level radar detectors utilize the use of microwave beams emitted by a sensor, which are then projected onto the surface of liquid in a tank. Waves hitting the surface of the fluid in the tank or vessel are able to return to the sensor which is installed on top of the tank or vessel. As the time it takes for the signal to travel back, also known as time of flight (TOF), is determined, it can be used to monitor the level of fluid in the tank. There are two main types of radar level measurement systems: passive and active.

FMCW systems 
Electronic module on top of the tank sends down a linear frequency sweep from which a sensor oscillator extracts a bandwidth and sweep duration fixed for the life of the system. When the reflected radar signal is received, it is delayed in proportion to the distance to the level surface. This occurs because the frequency of the sent signal is different from that of the received signal, and the two frequencies mix into a new frequency that is proportional to distance. 1 Now that we have found this new frequency, we can next utilize it to determine fluid level with incredible accuracy. The fundamental benefit of utilizing FMCW technology for level measurement in a tank is that the signals transmitted are FM instead of AM signals. While the majority of noise in a tank is found in the AM band, which is not involved with FM, the FM signals are not significantly impacted. Hence, as FMCW is the only method which can satisfy stringent accuracy criteria for tank gauging, FMCW is ideal for this purpose.

Pulsed radar systems 
Also referred to as pulsed time-of-flight systems, they are also known as pTOF systems. In essence, their functioning concept is pretty much like an ultrasonic level transmitter. The microwave technology emits a burst of energy towards the material to be treated. Because of the interaction between the skin and the tissue, this burst is manifested on the surface of the tissue and detected by the same sensor which now functions as a receiver. Microwave level is derived from the time it takes for the microwave signal to travel from transmission to reception. 2 In contrast to FMCW systems, which operate in a wide range of power, pulse radar systems have a relatively limited range of power. As a result, the effects of tank blockages and materials with low dielectric constants and foams is seen in their results.

Antenna Designs
You have the ability to select from two antenna designs depending on the application requirements and considering various factors, such as whether or not the tank is obstructed, whether or not vapors or foam are present, whether there is surface turbulence, and other physical properties of the liquid being measured. The size of the radar antenna is another critical consideration when determining the antenna's suitability for a given application. When the antenna's diameter is narrow, there will be larger beam divergence and more chance of undesired wave reflections from obstacles such as storage tanks. Conversely, for small antennas, the guided wave that returns to the sensor has a higher likelihood of travelling in that direction. On top of that, in small size antennas, the alignment of the sensor is not particularly significant. On the other hand, antennas with bigger diameters tend to provide a more focused and strong signal because they produce a smaller beam divergence. As well, they help to get rid of background noise disturbances that emerge from metallic surfaces that are flat and horizontal. The down side of having huge antennas is that they are more likely to be affected by repeated reflections from rough surfaces, tanks, and slopes. Some applications use the antennas that are placed on top of the tank to be completely enclosed and isolated for protective purposes.

Invasive Systems
The non-invasive approach utilized for liquid level measurement is called Guided-wave radar, and is referred to as the GWR method. In this technique, a cable or rod functions as a wave guide and guides the microwave from the sensor to the surface of the material in the tank, and then directly to the bottom. The basic underpinning of GWR is time-domain reflectometry (TDR), which has been in use for decades to find breaks in lengthy lengths of cable that are buried underground or embedded in the walls of buildings. A TDR generator creates more than 200,000 pulses of electromagnetic radiation that pass down the waveguide and are received on the other side. 3 Due to the process material's dielectric constant, the impedance of the process material varies, reflecting the wave back to the radar. Determine the amount of time it takes for the pulses to go down and reflect back is used to measure the fluid level. The in-band signal loss in this approach is remarkably low since the waveguide serves as a very efficient channel for signal propagation. Thus, in cases when materials have a very low dielectric constant, measuring of the level can be carried out effectively. Other complications associated with this invasive form of measuring include the usage of guide pulses, which means things like surface turbulence, foams, vapors, or tank blockages do not influence the measurement. This GWR approach is capable of working with a wide range of specific gravities and coatings. While it is assumed that the probe or rod used as a waveguide is not affected by the agitator blade or the corrosiveness of the fluid under measurement, there is always a possibility that the probe or rod used as a waveguide could be degraded by it.

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