TDR
TDR (Time Domain Reflectometry) is also known by many
other trade names such as “guided wave radar”, “radar on
a rope”, or “reflex radar”. TDR works on the same principle
as radar, except the signal is guided by a metal rod or
flexible cable, not through open air. The TDR transmits a
guided electromagnetic wave that travels at the speed of
light to the surface material and is then reflected back to the
electronic unit. The measurement is a time of flight calculation
determined by the transit time divided in half.
TDR has no calibration requirement and is well suited to
liquid, interface, and solid/granular measurements. It is not
affected by variations in process material and/or moisture
content. A key advantage of this technology is that the wave
travels along a rod or cable, eliminating signal propagation
losses. Users should be reminded that significant coating
deposits on the guide cable (or rod) may be a concern and
could affect the measurement. TDR has solved a number of
continuous level applications where variations in the head
space cause problems with non-contact technologies.