Importance

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Abstract

The occurrence of physical contact between a conductive probe and a surface of a liquid held in a container is detected as the probe is moved toward and eventually touches the liquid surface; a conductor is disposed on the other side of the container from the probe; an electrical signal is sent through the liquid between the conductive probe and the conductor, and the time when physical contact has occurred is determined based on when the resulting electrical signal which has passed through the liquid exceeds a threshold; and the threshold is determined based on the resulting electrical signal. In another aspect, the electrical signal is pulsed, and the resulting electrical signal is synchronously detected as the basis for determining when the physical contact has occurred. In another aspect, a non-conductive rotatable support holds the container and moves the container into position under the probe; a conductor is disposed beneath the rotatable support and in a fixed position relative to the rotatable support so that when the container is in position under the probe, the conductor lies beneath the container; the conductor has a limited extent so that when the container is not in that position no part of the conductor lies beneath the container.

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First Claim