Fundamentals of radar level measurement from Endress+Hauser.
The use of radar level measuring technology has proven itself over the years and since its introduction the popularity of this method has increased over conventional technologies. The term radar is an acronym for radio detecting and ranging; this measurement method determines the location and movement of an object using electromagnetic waves.
The emitted waves propagate at a known velocity of 300 000 km/s (the speed of light) in vacuum and unlike ultrasonic waves they do not require a propagation medium such as air. Radar level transmitters from Endress+Hauser use microwave pulses emitted by the antenna and reflected from the product surface whether it is liquid or bulk solid. The time of flight of the reflected radar pulse being directly proportional to the distance travelled. If the tank geometry is known, then the level can be calculated from the result.
Users demand safe and reliable measurement, particularly in the area of process instrumentation when using radar. Endress+Hauser offers two different instrument variants with operational frequencies of 6 GHz (C-band) and 26 GHz (K-band). These two variants offer optimal solutions for numerous applications, each frequency having its own specific advantages.
If high accuracy, reliability and limited vessel access is required, then the K-band with its horn antenna is appropriate for small storage, buffer and process tanks. Furthermore, the K-band (26 GHz) device can be used to achieve measurement ranges of up to 70 m for solids. The lower frequency or C-band devices offer advantages in applications where condensation or build-up might be present due to its lower susceptibility to interference.
Something to consider when using radar is that the reflection of the pulses occurs as a result of the change in the relative dielectric constant from air to the medium under measurement. The reflective properties of the medium are determined by the dielectric constant (DC) value. The table shows the allocation of DC values to various media.
The DC value of a medium is crucial since it can be a limitation to electromagnetic level measurement techniques. The higher the DC value, the better the reflection off the surface of the medium.
Non-contact radar level transmitters can be used in demanding applications where temperatures reach 400°C pressures up to 400 bar. An accuracy of 1 mm can be attained using specially calibrated radar transmitters for precision requirements in fuel tank farms – for instance, custody transfer.
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