US 5,627,522 A · Automated liquid level sensing system

Abstract

An automated liquid level sensing system for use in an automated, continuous, and random access analytical system is disclosed. A pipette probe is positioned above, and lowered into, a liquid sample container which contains the liquid to be detected. The probe is energized by a near radio-frequency (RF) signal source. A receiving antenna is positioned below the sample container, and is oriented so that very little signal is detected from the probe while the probe is in air. When the probe contacts liquid in the sample container, the electromagnetic field of the RF signal is increased and reoriented toward the receiving antenna. An autozero circuit maintains a near-zero output from the receiving antenna when slow changes in signal level occur due to changes in probe position or other environmental factors. The autozero circuit allows the sudden increase in signal amplitude, due to liquid contact, to pass to a receiver. A shield-driven triax cable connects the autozero circuit to the receiver, and significantly reduces the normal capacitance of the cable, enabling the signal change to be more easily detected.

Claims17

Dependent claims

An automated liquid level sensing system for detecting the presence of liquid in a container, said liquid level sensing system comprising:

a vertically oriented, electrically conductive probe positioned above said container;
means for vertically moving said probe into and out of said container;
a signal source electrically connected to said probe, said signal source capable of energizing said probe with an electrical signal and causing said probe to transmit said electrical signal at a given frequency;
a receiving antenna positioned below said container for receiving said transmitted electrical signal;
means for transferring said received electrical signal from said receiving antenna to an analyzing means;
means for analyzing said received electrical signal for indications that said probe has contacted liquid in said container, wherein said means for analyzing said received electrical signal includes:
(1) means for detecting changes in received signal amplitude, wherein said means for detecting changes in received signal amplitude includes:
(a) means for multiplying said received signal by a reference signal, said reference signal having a frequency substantially equal to the frequency of the transmitted signal;
and
(b) a low pass filter through which is passed said multiplied received signal;
and
(2) means for measuring rate of change of said change in received signal amplitude;
and
means connected to said analyzing means for indicating that liquid has been detected.

11 more elements

A method of automatically detecting the presence of liquid in a container, said method comprising the steps of:

vertically positioning an electrically conductive probe above said container;
vertically moving said probe into or out of said container;
causing a signal source, electrically connected to said probe, to energize said probe with an electrical signal, thereby causing said probe to transmit said electrical signal at a given frequency;
receiving said transmitted electrical signal with a receiving antenna positioned below said container;
transferring said received electrical signal from said receiving antenna to an analyzing means;
analyzing said received electrical signal for indications that said probe has contacted liquid in said container, wherein said step of analyzing said received electrical signal includes the steps of:
(1) detecting changes in received signal amplitude, wherein said step of detecting changes in received signal amplitude includes the steps of:
(a) multiplying said received signal by a reference signal, said reference signal having a frequency substantially equal to the frequency of the transmitted signal;
and
(b) passing said multiplied signal through a low pass filter;
(2) measuring the rate of change of said change in received signal amplitude;
and
indicating that liquid has been detected.

10 more elements

Dependencies are inferred from the claim text.

Automated liquid level sensing system

Life of this patent

Automated liquid level sensing system

Life of this patent

Abstract

Claims17