Patent ID: 7145349

Claim:
A method for increasing the interference resistance of a time domain reflectometer, comprising the steps of: generating a transmission pulse at a pulse repetition frequency; coupling said transmission pulse into a waveguide; scanning a reflected signal which is reflected back by a reflector in contact with the waveguide, for time-expanded display as a reflection profile with scanning pulses repeated at a scanning frequency; continuously obtaining measured values, from said reflection profiles, that contain the distance of the reflector to a process terminal; and using an algorithm for deciding the usability of said measured values, which from said measured values and the amount of interference calculates whether said reflection profile is sufficiently free of interference that adequate measurement accuracy is achieved, wherein: said scanning frequency and said pulse repetition frequency are varied; the time-expanded display of said reflection profiles remains unchanged, or if said reflection profiles change over time, the change in the time expansion is known and is taken into account in the evaluation of the profiles; and the amount of interference is determined from at least one measurement of said reflected profiles or a part thereof.