Capacitive sensing system and technique

摘要

An arrangement senses a liquid level by monitoring the peak capacitance formed between a probe and the liquid as the probe approaches or departs from the liquid. In an automated system, a computer controls the position of a pipette probe for aspirating or dispensing liquid in the vessel. The charge developed via the capacitance on the probe is coupled to a capacitive sensor circuit which provides a peak detector with an amplified signal representing the peak capacitance between the probe and the liquid. This amplified signal is detected by a peak-capacitance discrimination circuit, the output of which is monitored by the computer for determining the precise position of the probe with respect to the liquid surface level. Other aspects of the present invention include a negative-static elimination circuit coupled to the output of a detector latch and a positive-static elimination circuit coupled to the input of the detector latch.