Patent ID: 7318345
Filing Date: 2008-01-15
Classification: G01F

Abstract:
1. A method of measuring the height of a liquid using a high-frequency line probe ( 1 ), wherein there is implemented, on an electric circuit ( 3 ), supplied with a high-frequency alternating current, a comparison between the impedance of a coaxial or non-coaxial line probe ( 1 ) and a reference resistor ( 17 ), using a resistive measuring bridge ( 7 ), the probe ( 1 ) being submerged in a tank of fluid the height of which is to be determined forming one measuring arm of the measuring bridge and said reference resistor ( 17 ) forming an opposite arm of the measuring bridge, the comparison generating a comparison signal resulting from the alternate measurement of the signal on each of the measuring bridge arms using a detector, and through processing the comparison signal in order to obtain the calculation of the height of the liquid according to its permittivity, the length of the probe ( 1 ) and the circuit ( 3 ) power supply frequency, the processing of the comparison signal being performed in two stages comprised of a logarithmic amplifier stage ( 9 ) followed by a terminal differential amplifier stage ( 11 ), wherein said processing of the comparison signal implements a double synchronous switching ( 13 ), between the input ( 13 a ) of the logarithmic amplifier stage ( 9 ), and between the output ( 13 b ) of the logarithmic amplifier stage and the differential amplifier stage ( 11 ), so as to utilize a single logarithmic amplifier stage ( 9 ) for the first processing stage of the circuit.