Patent ID: 7891243

Claim:
A sensor for the contactless detection of the level of a liquid and adhering high-conductivity medium, especially blood, through a non-metal wall of a container characterized by: a pulse generator, ( 1 ) capable of generating a signal of non-inverted brief pulses and a separate signal of inverted brief pulses a first low-ohm resistor ( 2 ) which receives a signal of inverted brief pulses from said pulse generator, a second low-ohm resistor ( 3 ), equivalent to said first low-ohm resistor, which receives a signal of non-inverted brief pulses from said pulse generator, a first electrode ( 4 ) connected to said first low-ohm resistor ( 2 ) and actuated by said inverted brief pulses, a second electrode ( 5 ), identical to said first electrode, connected to said second low-ohm resistor ( 3 ) and actuated by said non-inverted brief pulses wherein said first and second electrodes are arranged next to each other at the same height relative to the filling level of the medium and on the outside wall of the container, a fast-action difference amplifier that has a high common-mode rejection ( 6 ) that taps a voltage drop caused by the filling level-dependent pulse current across said first resistor ( 2 ), wherein said difference amplifier amplifies said voltage drop by a fixed factor, a peak detector ( 7 ) connected to the output of said difference amplifier wherein said peak detector filters the output and obtains a filling level-dependent direct voltage, a first voltage comparator ( 8 ) connected to the output of the peak detector, which, by comparing the output voltage of the peak detector ( 7 ) to an adjustable setpoint voltage ( 9 ), generates a switching signal that changes from “low state” to “high state” as soon as a rising filling level causes the first and second electrodes ( 4 , 5 ) to be sufficiently covered and changes from “high state” to “low state” when the filling level sinks below the first and second electrodes ( 4 , 5 ) or reacts inversely to the change in the filling level as soon as the polarity of one of the components consisting of the pulse generator ( 1 ), the difference amplifier ( 6 ), the peak detector ( 7 ) and the first voltage comparator ( 8 ) is inverted.