US 4,736,638 AGranted

Liquid level sensor

AssigneeBeckman Instruments, Inc.

InventorsDobson Okawa, Wing S. Pang, Peter Kan

Life of this patent

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Abstract

Apparatus for sensing liquid levels in fluid transfer mechanisms and the like comprises a conductive member supporting containers for sample liquids, the conductive member being rotatably mounted for positioning selected containers under a conductive pipette probe. A low-frequency oscillator is capacitively coupled to the conductive member for generating an alternating electric field and producing an electrical signal at the probe. As the probe is lowered toward the liquid, an amplifier circuit monitors an electrical signal received by the probe. When the probe contacts the liquid, the amplifier detects a signal level in excess of a threshold level and produces an output signal for inhibiting the downward movement of the probe at the moment of contact with the liquid.

Claims7

Dependent claims

Apparatus for detecting physical contact between a conductive probe and an exposed surface of one of a plurality of liquid samples held in sample containers, the apparatus comprising:

(a) an oscillator including means for generating an alternating current signal;
(b) a stationary capacitive coupling member;
(c) means for coupling the alternating current signal to the stationary capacitive coupling member;
(d) a conductive member supporting the containers and disposed proximate the stationary capacitive coupling member whereby the alternating current signal is coupled to the conductive member and the conductive member couples the alternating current signal to all of the liquid samples supported by the conductive member;
(e) conductive member support and drive means for moveably supporting the conductive member and moving the conductive member and the containers disposed on the conductive member with respect to the stationary capacitive coupling member;
(f) amplifier means coupled to the probe for amplifying a signal received by the probe, the signal received by the probe including a signal produced by the alternating current signal;
and
(g) means responsive to the amplifier means for detecting a threshold level of the alternating current signal received by the probe indicative of contact between the probe and one of the liquid samples.

5 more elements

Dependencies are inferred from the claim text.

Facts

Application: 07/087,179Filed 19 Aug 1987 · continuation
Priority: 20 Dec 1985
Granted: 12 Apr 1988
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

G01N 35/1083
Characterised by the means for relatively moving the transfer device and the containers in an horizontal plane: with one horizontal degree of freedom
G01F 23/24
By measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of…:…
G01F 23/245
By measuring variations of resistance of resistors due to contact with conductor fluid: with a probe moved by an auxiliary power, e.g. meter, to…
G01N 2035/1025
Characterised by arrangements for controlling the aspiration or dispense of liquids: fluid level sensing