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Operating Principle of Non-Contacting Radar Level Sensor/Gauges (Unguided Wave)---Part two
Published:2017-08-07 | Browse: 1692 timesClose this page

Operating Principle of Non-Contacting Radar Level Sensor/Gauges (Unguided Wave)---Part two


Operating Principle of Non-Contact Radar Level Sensor


To measure the level of a liquid or solid in this type of radar instrument, radar signals are transmitted from the antenna of a radar instrument located at the top of the tank or vessel as shown below:

Non-contact level measurement using radar has two main modulation techniques: pulse radar and FMCW(Frequency Modulate Continuous Wave) radar techniques.

In the pulse radar technique, pulse radar sent out a microwave signal that bounces off the product surface and returns to the gauge. The transmitter measures the time delay between the transmitted and received echo signal and on-board microprocessor calculates the distance to the liquid surface using the formula:


Distance = [Speed of Light*Time Delay]/2


To calculate liquid level, the transmitter is programmed with the reference gauge height of the application (as show above)-usually the bottom of the tank or chamber. The liquid level is then calculated by the microprocessor in the transmitter.


In the FMCW radar technique, microwaves are transmitted towards the product surface, but the transmitted signal is of continuously varying frequency. When the signal has travelled down to the liquid surface and back to the antenna, it is mixed with the signal that is being transmitted at the same time. The difference in frequency between the received and transmitted signal is directly proportional to the distance to the liquid with high precision.


The frequency of non-contacting radar sensors can impact its performance. A lower frequency reduces sensitivity to vapor, foam and contamination of the antenna, whereas a higher frequency keeps the radar beam narrow in order to minimize influence from nozzles, walls and disturbing objects. Beam width is inversely proportional to antenna size. The beam width of a given frequency will decrease as the antenna size increase.


Non-contact radar sensor can be used in application from 1m to 70m.



 
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