Siemens Sitrans LR250 Operating Instructions Manual page 169

polarization error: the error arising from the transmission or reception of an electromagnetic
wave having a polarization other than that intended for the system.
PROFIBUS PA: one of the PROFIBUS family of protocols, specifically tailored for the needs of
process industries (PA = Process Automation).
propagation factor (pf): where the maximum velocity is 1.0, pf is a value that represents a
reduction in propagation velocity as a result of the wave travelling through a pipe or
medium.
pulse radar: a radar type that directly measures distance using short microwave pulses.
Distance is determined by the return transit time.
radar: radar is an acronym for RAdio Detection And Ranging. A device that radiates
electromagnetic waves and utilizes the reflection of such waves from distant objects to
determine their existence or position.
range: distance between a transmitter and a target.
range extension: the distance below the zero percent or empty point in a vessel.
relative permittivity: see dielectric constant.
repeatability: the closeness of agreement among repeated measurements of the same
variable under the same conditions.
shot: one transmit pulse or measurement.
speed of light: the speed of electromagnetic waves (including microwave and light in free
space. Light speed is a constant 299,792,458 meters per second.
stillpipe: a pipe that is mounted inside a vessel parallel to the vessel wall, and is open to the
vessel at the bottom.
stilling-well: see stillpipe.
two wire radar: a low-energy radar. Can be loop powered, analog, intrinsically safe, or a digital
(BUS) transmitter.
TVT (time varying threshold): a time-varying curve that determines the threshold level above
which echoes are determined to be valid.
waveguide antenna: a hollow, metallic tube that transmits a microwave signal to the product
target.
7ML19985JF04 SITRANS LR250 (PROFIBUS PA) – OPERATING INSTRUCTIONS Page 163