Patent ID: 6104200
Filing Date: 2000-08-15
Classification: G01N,G01R

Abstract:
Time Domain Reflectometry apparatus for measuring moisture characteristics of a material undergoing test using a material insertable probe coupled to said Time Domain Reflectometry apparatus by an RF cable with said probe having at least two parallel probe conductors spaced apart by, and integral with, an intermediate non-conductive dielectric spacer, said Time Domain Reflectometry apparatus comprising, in combination:a) means for generating a series of fast rise time pulses at a constant repetition rate and for propagating said pulses down said RF cable and said probe conductors so as to produce reflections from discontinuities located along the length of said probe conductors;b) means defining at least one remotely operable, normally open, variable impedance device coupled across said probe conductors at at least one known point for establishing at least one unambiguous precise timing marker;c) means for repetitively and remotely switching said at least one variable impedance device between the open non-conductive state and the shorted conductive state so as to establish said at least one unambiguous precise timing marker;d) means for sampling reflections from said probe conductors and for generating repetitive output signals having amplitudes proportional to the difference between the amplitude of the outputs from said sampling means arising from the impedance device open reflection at time T and the amplitudes of the outputs from said sampling means arising from the impedance device shorted reflection at time T; and,e) a synchronous detection circuit for processing signals output from said sampling means, said synchronous detection circuit including: i) amplifier means; ii) means for filtering the signal output from said sampling means; and iii), means for converting the amplified and filtered signal into a DC output signal V(T) representative of the difference function of the sample reflection waveform at at least one precise known timing marker;whereby, when said at least one variable impedance device is repetitively switched between the open non-conductive state and the shorted conductive state, said two probe conductors are repetitively and remotely shorted and opened at at least one known and fixed point to establish an unambiguous reflection at a precise known timing marker location T.sub.n so as to produce output signals from said sampling means as a result of remotely operable SHORTED/OPEN variable impedance device modulation.