SENSOR FOR THE CONTACTLESS DETECTION OF THE LEVEL OF AN ADHERING LIQUID MEDIUM OF HIGH-CONDUCTIVITY, ESPECIALLY BLOOD, THROUGH A NON-METALLIC WALL OF A CONTAINER AND CORRESPONDING METHOD

摘要

The invention relates to 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. Said sensor comprises a pulse generator (1) which generates short-period pulses which control an electrode (4), mounted on the exterior of the container wall, via a low-value resistor (2), a measuring resistor. A high common mode rejection differential amplifier (6) tapping a voltage drop on the measuring resistor (2) caused by the level-dependent pulsed current amplifies this voltage drop by a fixed factor and supplies the signal to a filtered down-stream peak value detector (7) for obtaining a level-dependent constant voltage and to a down-stream voltage comparator (8) which generates a switch signal by comparing the output voltage of the peak value detector (7) with an adjustable nominal voltage (9). Said switch signal changes from low level to high level as soon as the rising level sufficiently covers the electrode (4) or from high level to low level when the level falls below the electrode (4) or reacts inversely to a change in the level as soon as the polarity of one of the stages pulse generator (1), differential amplifier (6), peak value detector (7) and voltage comparator (8) are interchanged.