Automated liquid level sensing system

• US 5,627,522 A
• Filed: 01/03/1994
• Issued: 05/06/1997
• Est. Priority Date: 03/27/1992
• Status: Expired due to Term

• Current Assignee: Abbott Laboratories Incorporated
• Original Assignee: Abbott Laboratories Incorporated
• Inventors: Hills, David B., Walker, Donny R., Vaught, James A.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): LIEU, JULIE BICHNGOC
• Application Number:
  US08/176,610
• Time in Patent Office: 1,219 Days
• Field of Search: 340/618, 340/620, 340/539, 324/662, 324/663, 73/864.22, 73/864.24, 73/864.33, 73/427, 73/304 R, 422/62, 422/63, 422/100
• US Class Current: 340/618
• CPC Class Codes: B01F 31/24 the containers being submitted to a rectilinear movement
• CPC Class Codes: B01L 2200/142 Preventing evaporation
• CPC Class Codes: B01L 2300/042 Caps; Plugs
• CPC Class Codes: B01L 2300/043 Hinged closures
• CPC Class Codes: B01L 3/08 Flasks
• CPC Class Codes: B01L 3/5025 for parallel transport of multiple samples
• CPC Class Codes: B01L 3/5085 for multiple samples, e.g. microtitration plates
• CPC Class Codes: B01L 3/50853 with covers or lids
• CPC Class Codes: B01L 9/06 Test-tube stands; Test-tube holders
• CPC Class Codes: B29C 45/00 Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor injection blow-moulding B29C49/06
• CPC Class Codes: B29K 2995/0032 Birefringent
• CPC Class Codes: B29L 2023/22 Tubes or pipes, i.e. rigid bent tubes not for use as pipe couplings B29L2023/004
• CPC Class Codes: G01N 2001/007 Devices specially adapted for forensic samples, e.g. tamper-proofing, sample tracking
• CPC Class Codes: G01N 2021/6482 Sample cells, cuvettes
• CPC Class Codes: G01N 2035/00168 Manufacturing or preparing test elements
• CPC Class Codes: G01N 2035/00287 movable lid/cover for sample or reaction tubes
• CPC Class Codes: G01N 2035/00356 Holding samples at elevated temperature (incubation)
• CPC Class Codes: G01N 2035/00386 using fluid heat transfer medium
• CPC Class Codes: G01N 2035/00455 Controlling humidity in analyser
• CPC Class Codes: G01N 2035/00475 Filters
• CPC Class Codes: G01N 2035/00495 : Centrifuges
• CPC Class Codes: G01N 2035/00524 : Mixing by agitating sample carrier
• CPC Class Codes: G01N 2035/00752 : bar codes
• CPC Class Codes: G01N 2035/0093 : random access not determined by physical position
• CPC Class Codes: G01N 2035/0405 : manipulating closing or opening means, e.g. stoppers, screw caps, lids or covers
• CPC Class Codes: G01N 2035/0436 : with pre-packaged reagents, i.e. test-packs
• CPC Class Codes: G01N 2035/0441 : for samples
• CPC Class Codes: G01N 2035/0443 : for reagents
• CPC Class Codes: G01N 2035/0444 : for cuvettes or reaction vessels
• CPC Class Codes: G01N 2035/0446 : Combinations of the above
• CPC Class Codes: G01N 2035/0448 : composed of interchangeable ring elements
• CPC Class Codes: G01N 2035/0453 : Multiple carousels working in parallel
• CPC Class Codes: G01N 2035/0465 : Loading or unloading the conveyor
• CPC Class Codes: G01N 2035/1025 : Fluid level sensing
• CPC Class Codes: G01N 2035/1076 : plurality or independently movable heads
• CPC Class Codes: G01N 2035/1086 : Cylindrical, e.g. variable angle
• CPC Class Codes: G01N 21/03 : Cuvette constructions
• CPC Class Codes: G01N 21/253 : for batch operation, i.e. multisample apparatus analytical automats G01N35/00
• CPC Class Codes: G01N 21/645 : Specially adapted constructive features of fluorimeters
• CPC Class Codes: G01N 21/76 : Chemiluminescence; Bioluminescence
• CPC Class Codes: G01N 33/53 : Immunoassay; Biospecific binding assay; Materials therefor
• CPC Class Codes: G01N 33/5302 : Apparatus specially adapted for immunological test procedures
• CPC Class Codes: G01N 33/537 : with separation of immune complex from unbound antigen or antibody
• CPC Class Codes: G01N 33/538 : by sorbent column, particles or resin strip , i.e. sorbent materials
• CPC Class Codes: G01N 33/542 : with steric inhibition or signal modification, e.g. fluorescent quenching
• CPC Class Codes: G01N 33/54313 : the carrier being characterised by its particulate form
• CPC Class Codes: G01N 35/0092 : Scheduling
• CPC Class Codes: G01N 35/0099 : comprising robots or similar manipulators robots per se B25J
• CPC Class Codes: G01N 35/025 : having a carousel or turntable for reaction cells or cuvettes
• CPC Class Codes: G01N 35/1004 : Cleaning sample transfer devices
• CPC Class Codes: G01N 35/1065 : Multiple transfer devices
• CPC Class Codes: H01J 49/04 : Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components

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.

Claims

1. 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.

2. The automated liquid level sensing system of claim 1 further comprising means for comparing said received signal amplitude to a predetermined threshold value.

4. The automated liquid level sensing system of claim 1, wherein said means for transferring said received electrical signal from said receiving antenna to said analyzing means includes a triax cable having an outer conductor, and inner shield, and an inner conductor.

5. The automated liquid level sensing system of claim 4, wherein said means for detecting changes in received signal amplitude includes means for reducing the effective capacitance of said triax cable.

6. The automated liquid level sensing system of claim 5, wherein said means for reducing the effective capacitance of said triax cable includes a driven shield circuit connected to said inner shield of said triax cable, said circuit providing a buffer which drives said inner shield.

7. The automated liquid level sensing system of claim 1 further comprising a fluid level sensing sleeve, said sleeve channelling said electrical signal from said probe to said receiving antenna.

8. The automated liquid level sensing system of claim 7, wherein said sensing sleeve is a conductive cylinder having first and second ends, said first end surrounding said liquid container, and said second end mounted adjacent said receiving antenna.

3. 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;

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 comparing amplitude of said received signal to a predetermined threshold value;

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 change 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; 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, wherein said means for detecting changes in received signal amplitude further comprises;

means for reducing said received signal amplitude to a value below said predetermined threshold value when said received signal amplitude changes slowly; and

means for passing said received signal to said means for comparing said received signal amplitude to a predetermined threshold value when said received signal amplitude changes rapidly.

9. 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. The method of automatically detecting the presence of liquid in a container of claim 9 further comprising the step of comparing said received signal amplitude to a predetermined threshold value.

11. The method of automatically detecting the presence of liquid in a container of claim 9, wherein said step of transferring said received electrical signal from said receiving antenna to said analyzing means includes the step of transferring said signal over a triax cable having an outer conductor, an inner shield, and an inner conductor.

12. The method of automatically detecting the presence of liquid in a container of claim 11, wherein said step of detecting changes in received signal amplitude includes the step of reducing the effective capacitance of said triax cable.

13. The method of automatically detecting the presence of liquid in a container of claim 12, wherein said step of reducing the effective capacitance of said triax cable includes the step of connecting a driven shield circuit to said inner shield of said triax cable, said circuit providing a buffer which drives said inner shield.

14. The method of automatically detecting the presence of liquid in a container of claim 9 further comprising the step of channelling said electrical signal from said probe to said receiving antenna utilizing a conductive fluid level sensing sleeve having first and second ends.

15. The method of automatically detecting the presence of liquid in a container of claim 14, wherein said step of channelling said electrical signal from said probe to said receiving antenna includes the steps of:

surrounding said liquid container with said first end of said sensing sleeve; and

mounting said second end of said sensing sleeve adjacent said receiving antenna.

16. An automated liquid sensing system for use in a clinical analysis system having a pipettor for dispensing or aspirating liquid in a container, the pipettor being electrically conductive and moveable vertically into the container, said automated liquid sensing system comprising:

means electrically connected to the pipettor for applying a RF signal thereto and causing the pipettor to radiate an electromagnetic field, the propagation of which changes when the pipettor contacts the surface of the liquid in the container;

antenna means positioned below the container substantially parallel to the surface of the liquid for receiving the electromagnetic field and providing a received signal responsive to the change in propagation of the electromagnetic field; and

means electrically connected to said antenna means for analyzing the received signal and providing an output signal corresponding to the change in the propagation of the electromagnetic field whereby the output signal represents the position at which the pipettor contacts the liquid, 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 applied 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.

17. 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;

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;

comparing said received signal amplitude to a predetermined threshold value;

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; 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, wherein said step of detecting changes in received signal amplitude further comprises the steps of;

reducing said received signal amplitude to a value below said predetermined threshold value when said received signal amplitude changes slowly; and

passing said received signal to said means for comparing said received signal amplitude to a predetermined threshold value when said received signal amplitude changes rapidly.