Patent ID: 7334451

Claim:
A method of detecting a weak interface signal in a guided wave level measurement device comprising a waveguide, a signal generator and a signal receiver, the signal generator and signal receiver operationally connected to the waveguide, said device emitting signals from said signal generator to be received as reflected signals at said signal receiver, wherein the method comprises the steps of (a) monitoring one of said received reflected signals (S 1 ) to detect a first signal level that exceeds or equals a first predetermined threshold level (TH 1 ) and detecting said first signal level at elapsed signal time T 1 ; (b) monitoring one of said received reflected signals (S 2 ) to detect a second signal level that exceeds or equals a second predetermined threshold level (TH 2 ), where TH 2 equals or exceeds said TH 1 ; (c) monitoring one of said received reflected signals (S 3 ) to detect a third signal level that equals or exceeds a third signal threshold level (TH 3 ) where TH 3 is less than TH 2 ; (d) if detection is made of said signal levels at TH 3 but not TH 2 , transmitting an indicator of failure to detect, in said received reflected signals, said second signal levels.