Kobold NRM, Operating Manual

Page: 5 / 52

NRM
NRM K06/0422 page 5
5. Operating Principle
The reflection of the emitted microwave impulses is considerably depending on the
relative dielectric constant of the measured medium. The essential condition of
microwave level measurement is that the relative dielectric constant (εr) of the
medium should be more than 1.9.
The operation of the non-contact microwave level transmitters is based on the
measurement of the time of flight of the reflected signals, so-called Time Domain
Reflectometry (TDR) method.
The propagation speed of microwave impulses is practically the same in air, gases
and in vacuum, independently from the process temperature and pressure, so the
measured distance is not affected by the physical parameters of medium to be
measured.
The NRM level transmitter is a Pulse Burst Radar operating at 25 GHz (K-band)
microwave frequency.
The 25 GHz models’ most noticeable advantage over the lower frequency
(5-12 GHz) radars are the smaller antenna size, the better focusing, lower
dead-band and smaller transmission angle.
The level transmitter induces few nanosecond length microwave impulses in the
antenna and a part of the energy of the emitted signals reflects back from the
measurement surface depending on the measured media. The time of flight of the
reflected signal is measured and processed by the electronics, and then this is
converted to distance, level or volume proportional data.