Patent ID: 6328934
Filing Date: 2001-12-11
Classification: G01F,G01N

Abstract:
A device for detecting when a test probe of conducting material contacts a liquid surface, comprising a test probe of conducting material, wherein the test probe is electrically screened by an insulated screen, with part of the test probe projecting in front of the screen, and further wherein:the test probe is connected to a first alternating voltage source via a first impedance and to one input of a differential amplifier, and the screen is connected to a second alternating voltage source via a second impedance and to another input of the differential amplifier,an output of the differential amplifier is connected to one input of a first multiplicator and to one input of a second multiplicator, and another input of the first multiplicator is connected to a third alternating voltage source, and another input of the second multiplicator is connected to a fourth alternating voltage source,an output voltage of the fourth alternating voltage source is phase shifted relative to an output voltage of the third alternating voltage source; anda signal processing unit is connected to the outputs of the first and second multiplicators and is capable of, based on the output signals of the multiplicators, deriving a first signal representing the resistive load of the test probe and a second signal representing the capacitive load of the test probe, and, when the resistive load is low and the capacitive load is high, providing a signal as an indication that the test probe has contacted a liquid surface.