# US 5,705,815 A · Device for the detection of liquid surfaces

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- Number: US 5,705,815 A
- Document ID: US5705815A
- Status: Granted
- Kind: A
- Application number: 08/599,876
- Filed: 1996-02-12
- Granted: 1998-01-06
- Earliest claimed: 1995-02-11
- Assignees: Boehringer Mannheim GmbH
- Inventors: Stefan Heesch
- Web page: https://patentgrep.com/patent/US5705815A

## CPC

- G01F 23/292: Light {, e.g. infrared or ultraviolet}
- G01F 23/2928: {using light reflected on the material surface}
- Y10S 250/90: Optical liquid level sensors
- Y10S 250/901: with gap between light guide elements, includes open light path preset
- G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

Device for the detection of liquid surfaces including a light source sending light onto a liquid surface, an oscillation element which is moved toward the liquid surface and causes the liquid surface to oscillate upon contact with the surface. The surface contact is detected by a light detector which picks up the radiation reflected by the liquid. Upon contact with the liquid, the light sent out by the light source is modulated by the oscillations of the liquid surface. The so modulated signal can be selectively identified by the detector.

## Claims

### Claim 1

A device for detecting a liquid surface, said device comprising:
a light source disposed above a liquid surface to be detected;
detector means above said liquid surface, said detector means for detecting light from said light source which is reflected by the liquid surface, said detector means generating a detection signal based upon the light detected thereby;
oscillation means disposed above the liquid surface, said oscillation means for contacting the liquid surface;
excitation means coupled to said oscillation means, said excitation means for exciting said oscillation means and transmitting an oscillation thereto;
drive means coupled to said oscillation means for moving said oscillation means to and from the liquid surface;
filter means coupled to said detector means, said filter means receiving the detection signal and outputting a filtered signal by filtering interfering signals therefrom; and
evaluation means coupled to said filter means, said evaluation means detecting a contact between the oscillation means and the liquid surface, the contact being detected based upon the filtered signal.

### Claim 2 (depends on 1)

A device as recited in claim 1, wherein said filter means comprises a frequency band filter.

### Claim 3 (depends on 1)

A device as recited in claim 1, further comprising a first light guide for guiding light from said light source onto the liquid surface.

### Claim 4 (depends on 3)

A device as recited in claim 3, further comprising a second light guide for guiding light reflected from the liquid surface to said detector means.

### Claim 5 (depends on 4)

A device as recited in claim 4, wherein said first and second light guides include first and second axes, respectively, said first and second axes being disposed substantially in parallel.

### Claim 6 (depends on 4)

A device as recited in claim 4, wherein said first and second light guides include first and second axes, respectively, said first and second axes being disposed at an acute angle with respect to each other.

### Claim 7 (depends on 4)

A device as recited in claim 4, wherein said drive means moves said first and second light guides to and from the liquid surface, in addition to the oscillation means.

### Claim 8 (depends on 4)

A device as recited in claim 4, further comprising moving means to move ends of said first and second light guides perpendicularly to the liquid surface.

### Claim 9 (depends on 8)

A device as recited in claim 8, wherein said moving means comprises connecting means for connecting said first and second light guides to said drive means.

### Claim 10 (depends on 1)

A, device as recited in claim 1, further comprising moving means to move said light source and said detector perpendicularly to the liquid surface.

### Claim 11 (depends on 8)

A device as recited in claim 8, wherein said moving means comprises a connecting member connecting said light source and said detector to said drive means.

### Claim 12 (depends on 1)

A device as recited in claim 1, wherein said drive means is configured to move said light source and said detector means to and from the liquid surface.

### Claim 13 (depends on 1)

A device as recited in claim 1, wherein said oscillation means oscillates at a frequency between 100 Hz and 1 kHz.

### Claim 14 (depends on 1)

A device as recited in claim 1, wherein said filter means is configured to filter frequencies which do not correspond to an oscillation frequency of said oscillation means, thereby passing a frequency which corresponds to the frequency of the oscillation means.

### Claim 15 (depends on 1)

A device as recited in claim 1, wherein said evaluation means controls the drive means to move the oscillation means to and from the liquid surface based upon the detection signal.

### Claim 16 (depends on 1)

A device as recited in claim 1, wherein said light source provides modulated light.

### Claim 17 (depends on 1)

A device as recited in claim 1, wherein said oscillation means comprises a pipette tip.

### Claim 18

A method for the detection of a surface of a liquid, said method comprising the steps of:
oscillating an oscillating member above a liquid surface;
moving said oscillating member toward the liquid surface;
exposing a liquid surface to be detected to light from a light source;
detecting light from said light source which has been reflected from said liquid surface with a detector means, wherein said detector means generates a detection signal;
filtering the detection signal, thereby producing a filtered signal;
determining contact between the oscillating member and the liquid surface based upon the filtered signal.

### Claim 19 (depends on 18)

A method as recited in claim 18, further comprising the step of stopping the movement of the oscillating member after the contact between the oscillating member and the liquid surface has been detected.

### Claim 20 (depends on 18)

A method as recited in claim 18, further comprising a step of stopping the movement of the oscillating member after the oscillating member has moved downward by a predetermined distance after the contact between the oscillating member and the liquid surface has been detected.

### Claim 21 (depends on 18)

A method as recited in claim 18, further comprising a step of pipetting liquid after the contact has been detected.

### Claim 22 (depends on 18)

A method as recited in claim 18, further comprising a step of rectifying the filtered signal to generate a rectified voltage, and comparing the rectified voltage with a reference voltage, wherein contact between the oscillating member and the liquid surface is detected when the rectified voltage exceeds the reference voltage.

### Claim 23

A method for detecting a liquid surface, said method comprising the steps of:
providing a light source and a detector above a liquid surface, said detector for detecting light from the light source which is reflected by the liquid surface, with the detector generating a detection signal based upon the light detected thereby;
providing an oscillating member above the liquid surface, said oscillating member being movable to and from the liquid surface;
providing an excitation means for exciting said oscillating member, by translating an oscillation thereto; said method further comprising the steps of
oscillating said oscillating member through excitation of the excitation means;
moving the oscillating member toward the liquid surface;
radiating light from the light source toward the liquid surface;
detecting light reflected from the liquid surface with the detector such that the detector generates the detection signal;
filtering the detection signal with a filtering means, and outputting a filtered signal therefrom;
determining a contact between the oscillating element and the liquid surface based upon the filtered signal.