LEVEL SENSOR APPARATUS FOR DETECTING CONTACT OF A PIPETTING NEEDLE WITH A LIQUID IN A VESSEL

摘要

A level sensor apparatus for detecting contact of a pipetting needle with a liquid contained in a vessel. The apparatus comprises: (a) a sensor head having a mechanical resonance frequency and including, (a.1) a pipetting needle (12), (a.2) a needle holder (14) for holding said pipetting needle (12), (a.3) an electromechanical transducer (15) mechanically connected with said pipetting needle (12), (b) electrical signal generating means (16) for generating a driving signal and for applying this signal to said electromechanical transducer (15) for causing vibration of said pipetting needle (12) at said resonance frequency, (c) means for measuring an electrical signal provided by said electromechanical transducer (15), said signal being representative of the vibration of said pipetting needle (12) when it is driven by said driving signal, and (d) means (17) for evaluating the variation of said parameter with time for detecting contact of the pipetting needle (12) with a liquid (28) contained in said vessel (11) and for providing a resulting signal representative of the result of said evaluation.