Interface measuring apparatus

Claim 2

In an apparatus for measuring the location of an unknown interface separating two media having different dielectric constants, a transmission line positioned across said interface, a switch connected between ground and a reference interface on the center conductor of said transmission line, a signal generator for generating a fast rising output pulse which is reflected from the unknown interface when the switch is open and which is reflected from the reference interface when the switch is closed, the improvement comprising: a switch driver for closing and opening said switch, a frequency monitor for measuring the frequency of the pulses reflected from said reference interface and for measuring the frequency of the pulses reflected from said unknown interface, to thereby obtain a measurement of said unknown interface, and means coupling said frequency monitor to said switch driver to automatically open said switch after measurement of said reference interface.

Claim 3

In an apparatus for measuring the location of an unknown interface separating two media having different dielectric constants, a transmission line positioned across said interface, a switch connected between ground and a reference interface on the center conductor of said transmission line, a pulse generator applying a fast rising output pulse to said center conductor which is reflected from the unknown interface when the switch is open and which is reflected from the reference interface when the switch is closed, the improvement comprising: a first delay network coupled to the output of said pulse generator to separate in the time domain the applied pulse from the reflected pulse during each measurement cycle; a comparator amplifier having two input terminals, the reflected pulse being applied to one of said input terminals and the other input terminal being connected to a reference potential, said comparator amplifier generating an output pulse when the amplituDe of the reflected pulse falls below the reference potential; a flip-flop network coupled to the output of said comparator amplifier, the output pulse from said comparator amplifier changing the original state of said flip-flop network; a second delay network connected between the input and output of said flip-flop for resetting the flip-flop to its original state and simultaneously retriggering said pulse generator to produce another pulse; the reflected pulse from said other pulse returning to said one terminal of said comparator amplifier to again reset the flip-flop to start another measurement cycle whereby oscillations are established around said pulse generator, the base frequency of such oscillations corresponding to the reference interface when said switch is closed and to said unknown interface when said switch is open; an interface monitor coupled to said flip-flop for measuring the corresponding frequencies during a predetermined time interval to obtain an accurate measurement of said reference and unknown interfaces; and a switch controller coupled to said interface monitor for automatically opening and closing said switch in response to the measured frequencies.

Claim 4

In an apparatus for measuring the location of an unknown interface separating two media having different dielectric constants, a transmission line positioned across said interface, a switch connected between ground and a reference interface on the center conductor of said transmission line, a pulse generator applying a fast rising output pulse to said center conductor which is reflected from the unknown interface when the switch is open and which is reflected from the reference interface when the switch is closed, the improvement comprising: a first delay network coupled to the output of said pulse generator to separate in the time domain the applied pulse from the reflected pulse during each measurement cycle; a comparator amplifier having two input terminals, the reflected pulse being applied to one of said input terminals and the other input terminal being connected to a reference potential, said comparator amplifier generating an output pulse when the amplituDe of the reflected pulse falls below the reference potential; a flip-flop network coupled to the output of said comparator amplifier, the output pulse from said comparator amplifier changing the original state of said flip-flop network; a second delay network connected between the input and output of said flip-flop for resetting the flip-flop to its original state and simultaneously retriggering said pulse generator to produce another pulse; the reflected pulse from said other pulse returning to said one terminal of said comparator amplifier to again reset the flip-flop to start another measurement cycle whereby oscillations are established around said pulse generator, the base frequency of such oscillations corresponding to the reference interface when said switch is closed and to said unknown interface when said switch is open; an interface monitor coupled to said flip-flop for measuring the corresponding frequencies during a predetermined time interval to obtain an accurate measurement of said reference and unknown interfaces; and a switch controller coupled to said interface monitor for automatically opening and closing said switch in response to the measured frequencies.