Siemens SITRANS LR250 Instruction Manual page 128

derating: to decrease a rating suitable for normal conditions according to guidelines specified
for different conditions.
dielectric: a nonconductor of direct electric current.
dielectric constant (DK): the ability of a dielectric to store electrical potential energy under the
influence of an electric field. Also known as Relative Permittivity. An increase in the
dielectric constant is directly proportional to an increase in signal amplitude. The value is
usually given relative to a vacuum /dry air: the dielectric constant of air is 1
echo: a signal that has been reflected with sufficient magnitude and delay to be perceived in
some manner as a signal distinct from that directly transmitted. Echoes are frequently
measured in decibels relative to the directly transmitted signal.
echo confidence: the recognition of the validity of the echo. A measure of echo reliability.
Echo Lock Window: a window centered on an echo in order to locate and display the echo's
position and true reading. Echoes outside the window are not immediately processed.
Echo Marker: a marker that points to the processed echo.
Echo Processing: the process by which the radar unit determines echoes.
Echo Strength: describes the strength of the selected echo in dB above 1 µV rms.
Echo Profile: a graphical display of a processed echo.
false echo: any echo which is not the echo from the desired target. Generally, false echoes are
created by vessel obstructions.
frequency: the number of periods occurring per unit time. Frequency may be stated in cycles
per second.
hertz (Hz): unit of frequency, one cycle per second. 1 Gigahertz (GHz) is equal to 10
HART: Highway Addressable Remote Transducer. An open communication protocol used to
address field instruments.
horn antenna: a conical, horn-shaped antenna which focuses microwave signals. The larger
the horn diameter, the more focused the radar beam.
inductance: the property of an electric circuit by virtue of which a varying current induces an
electromotive force in that circuit or in a neighboring circuit. The unit is a Henry.
microwaves: the term for the electromagnetic frequencies occupying the portion of the radio
frequency spectrum from 1 GHz to 300 GHz.
1. Many conductive liquids/electrolytes exhibit dielectric properties; the relative dielec-
tric constant of water is 80.
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