TDR Time domain reflectometry

A technique for measuring cable lengths by timing the period between a test pulse and the reflection of the pulse from an impedance discontinuity on the cable. The returned waveform reveals undesired cable conditions, including shorts, opens, and transmission anomalies due to excessive bends or crushing. The length to any anomaly, including the unterminated cable end or cable break, may be computed from the relative time of the wave return and nominal velocity of propagation of the pulse through the cable. For optical fiber cables, see also optical time-domain reflectometry.