Regarding guided-wave radar level gauges
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Dear seniors, hello. I’m quite confused about guided-wave radar level gauges, and I’d like to understand what happens when the dielectric constant is low And why this is the case. I checked Baidu Baike’s description of it, which states that it has an inhibitory effect on steam and foam; I don’t understand how this inhibition works. I’m asking a senior who knows the answer to explain it; thank you
With a mindset of learning*. Is there also a relationship between guided-wave radar level gauges and dielectric constant? ····Just use it···
Yes, there are requirements regarding the dielectric constant; it seems that performance is not good when it’s below 1.4. Measuring the liquid level in the presence of foam and steam, guided wave sensing is suitable.
Yes, if the dielectric constant is too low, the radar will not be able to detect any reflected echoes; therefore, the dielectric constant is taken into consideration when selecting a suitable product. If there is steam or foam on the surface above the liquid level, the radar waves from the non-contact radar cannot penetrate through that layer, and it becomes impossible to measure the actual surface of the liquid. Not only is measurement impossible, but the radar may also produce no output at all, as no echo signals are detected; in such cases, the only possible outputs are the maximum or minimum values
I also want to ask what the concept of dielectric constant is, and why a low value prevents the generation of reflected echoes. Also, if the dielectric has layers, why must the dielectric constant of the lower layer be more than 10 times higher than that of the upper layer?
When a dielectric is exposed to an external electric field, it generates induced charges that weaken the electric field. The ratio of the original external electric field (in vacuum) to the electric field within the dielectric is known as the relative permittivity (or dielectric constant), also referred to as the permittivity, and it varies with frequency. The dielectric constant is the product of the relative dielectric constant and the absolute dielectric constant in a vacuum. The above is from Baidu. The signal detected by guided-wave radar is actually caused by changes in the dielectric constant. The lower the dielectric constant of a medium, the closer it is to that of air, which means the weaker the signal generated and the easier it is to be overwhelmed by interference signals. The same applies to layered media.
The dielectric constant is an important factor affecting radar waves, just like conductivity – some materials have good conductivity while others have slightly poorer conductivity. The same is true for the dielectric constant: the lower the dielectric constant, the greater the attenuation of radar waves, resulting in fewer returning waves, and thus the radar is unable to detect any echo signals. You mentioned the radar used for measuring boundaries again. For such boundaries, it’s necessary that there be a significant difference in dielectric constants between the upper and lower layers; it seems that an emulsified layer is formed in between. I’m not quite sure about this – I’ll go and learn more about it
Your explanation, along with what I found by searching on Baidu, finally helped me understand that the higher the dielectric constant, the stronger the insulating properties of the material, and the greater its reflectivity of electromagnetic waves. When interface measurement is performed, the dielectric constant of the upper medium cannot be too high; if it is too high, electromagnetic waves cannot reach the interface of the lower layer of medium. Since the electromagnetic waves have already passed through the upper layer of medium and some of them are reflected, the energy of these electromagnetic waves is reduced. Therefore, the dielectric constant of the lower layer of medium should be as high as possible (as more waves are reflected, the higher the measurement accuracy).
Thank you, I checked it later as well. Does guiding the wave have no impact? I know that flared shapes have an impact. Does it matter whether waveguiding occurs or not?