Siemens Sitrans LR400 Instruction Manual page 110

PELV: Protected Extra Low Voltage
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.
PTFE: Polytetrafluorethylene
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.
repeatability: the closeness of agreement among repeated measurements of the same
variable under the same conditions.
SELV: Safety Extra Low Voltage
shot: one transmit pulse or measurement.
Signal-to-noise ratio: measure of the strength of reflection of the measuring medium in the
current measuring situation in dB.
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.
SSC/ASC: synchronous serial communications/asynchronous serial communications
stillpipe: a pipe that is mounted inside a vessel perpendicular to the vessel wall, and is open to
the vessel at the bottom.
stilling-well: see stillpipe.
TVT (time varying threshold): a time-varying curve that determines the threshold level above
which echoes are determined to be valid.
URV: Upper limit of the valid measuring range as a distance from the bottom inside of the
vessel
validity: measure of the certainty of the current measured value in %.
waveguide antenna: a hollow, metallic tube that transmits a microwave signal to the product
target.
Page 106 SITRANS LR400 (7ML5421) – INSTRUCTION MANUAL 7ML19985FH06