Patent ID: 6307380
Filing Date: 2001-10-23
Classification: G01D,G01F

Abstract:
A distance measuring apparatus comprising: a parallel conductor which is simulated as in an impedance equivalent state and of which the propagation speed of voltage is known and having one end thereof to which a high-frequency pulse is introduced; and an impedance mismatch generator arranged to produce an impedance change at a specific portion of the parallel conductor by exposing one of an inductance L, a resistance R and a static capacitance C at a location of one of close and directly to the parallel conductor and mounted to an intermediate region of the parallel conductor, wherein as a primary reflected wave of the introducing pulse is generated at the location of the impedance mismatch generator, a duration from the introduction of the pulse to the receipt of the primary reflected wave at the one end is measured and multiplied by the propagation speed of voltage to determine a distance between the one end of the parallel conductor where the pulse is introduced and the location of the impedance mismatch generator and when it is assumed that the overall length of a sensor cable is LM, the leading distance is L0, the distance between the one end of the sensor cable and the location of the impedance mismatch generator is L1, and the reference voltage is a threshold E0, the measurement is made by applying the introducing pulse and simultaneously directing a saw-teeth waveform generator to generate a saw-teeth wave voltage, and when the comparator detects that a primary reflected wave of E1 exceeds the threshold E0, pausing a boosting action of the saw-teeth wave voltage and saving its voltage level which represents the distance between the one end of the sensor cable and the location of the impedance mismatch generator.