Hybrid conductivity sensor

• US 9,410,910 B1
• Filed: 05/23/2014
• Issued: 08/09/2016
• Est. Priority Date: 05/23/2013
• Status: Active Grant

• Current Assignee: D-2, Inc.
• Original Assignee: D-2, Inc.
• Inventors: Fougere, Alan J
• Primary Examiner(s): Natalini, Jeff
• Application Number:
  US14/286,557
• Time in Patent Office: 809 Days
• Field of Search: 324/439
• US Class Current: 1/1
• CPC Class Codes: G01N 27/06 of a liquid involving electrolysis G01N27/26
• CPC Class Codes: G01N 33/18 Water
• CPC Class Codes: G01N 9/00 Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity

Abstract

A sensor for measuring conductivity of a fluid containing dissolved ions, particularly for measuring conductivity of salt water, features a cylindrical tube (57) of poorly conductive material such as glass, a first electrode (51A) and a second electrode (51B) inside the tube, connected together (56) to maintain a common electrical potential, a first transformer (52,53) concentrically arranged around the tube (57) to drive current through the fluid in the tube, and a second transformer (54, 55) arranged to sense a value of the current flowing in the fluid, and a digital processing circuit (62) coupled to receive an output signal of the second transformer, and to derive therefrom a value representing the conductivity of the fluid. The sensor is adapted to be towed behind a research ship, or to be deployed on an autonomous underwater vehicle (AUV) or the like. Current signals are preferably processed by digital switching measurement technology (dMST).

Claims

1. A sensor for measuring electrical conductivity of a fluid containing dissolved ions, comprising

a generally cylindrical tube (57) of poorly electrically conductive material, having a first, inlet end, an intermediate portion, and a second, outlet end;

a first toroidal transformer (52) with winding (53) arranged around said tube, near said first end, for applying, during operation, an electromagnetic voltage field to fluid within said tube, to drive a measurement current to flow through fluid in the cylindrical tube (57);

a first annular electrode (51A), arranged inside said tube, near said first end;

a second annular electrode (51B), arranged inside said tube, near said second end;

an electrical conductor (56) interconnecting said first and second electrodes, in order to maintain said electrodes at a common electrical potential with each other, and to provide a lowest-resistance path for the measurement current to flow;

a second toroidal transformer (54) with winding (55), arranged such that the electrical conductor (56) forms a turn around the second toroidal transformer, to sense a value of current in fluid in said tube (57);

a source of a time-varying periodic electrical signal, coupled to said first toroidal winding (53); and

a digital computing device (68), coupled to an output of said second toroidal winding (55), configured to derive, during operation, from an output signal of said second toroidal winding, a current value representing instantaneous electrical conductivity of said fluid within said tube (57).

2. The sensor of claim 1, wherein said time-varying periodic electrical signal is an alternating current (AC) signal.

3. The sensor of claim 1, wherein the digital computing device filters and integrates successively received current values from said second toroidal winding.

4. The sensor of claim 1, wherein said digital computing device (68) comprises

an analog-to-digital converter;

a detector configured to detect a phase of said AC signal applied to said drive transformer (52,53); and

a modulator adapted to generate a feedback current signal, for application to said current sense transformer (54,55), to at least periodically null magnetic flux therein.

5. The sensor of claim 4,

further comprising

an automatic gain control and a band-pass filter, interposed between said analog-to-digital converter and said phase detector.

6. The sensor of claim 4, further comprising an integrator, interposed between said phase converter and said modulator.

7. The sensor of claim 4, wherein said digital computing device is a digital signal processor (DSP) configured to process conductivity data, temperature data, and pressure data, according to an equation of state algorithm,

to thereby derive oceanographic salinity and density values.

8. A sensor for measuring electrical conductivity of a fluid containing dissolved ions, comprising

a generally cylindrical tube (57) of poorly electrically conductive material, having a first, inlet end, an intermediate portion, and a second, outlet end;

a first toroidal core (52) with winding (53) arranged around said tube, near said first end, for applying, during operation, an electromagnetic field to fluid within said tube, which produces a measurement current flowing in the cylindrical tube (57);

a first annular electrode (51), arranged inside said tube, near said first end;

a second annular electrode (51), arranged inside said tube, near said second end;

an electrical conductor (56) interconnecting said first and second electrodes, in order to maintain said electrodes at a common electrical potential with each other, and, to provide the lowest resistance path for the measurement current to flow;

a second toroidal core (54) with winding (55), arranged such that the electrical conductor (56) forms a turn around the second toroidal core;

a source of a time-varying periodic electrical signal, coupled to said first toroidal winding (53);

a pressure-protective housing (61) mechanically connected to said tube (57), said housing (61) surrounding a digital computing device (68), coupled to an output of said second toroidal winding (55), configured to derive, during operation, from an output signal of said second toroidal winding (55), a current value representing instantaneous electrical conductivity of said fluid within said tube.

9. The sensor of claim 8, wherein said pressure-protecting housing (59, 61) is mechanically coupled to an intermediate portion of said tube (57) and extends laterally therefrom.

10. The sensor of claim 8, further comprising

a generally cylindrical first end guard concentrically surrounding said inlet end of said tube;

a generally cylindrical second end guard concentrically surrounding said outlet end of said tube; and

an oil-filled central housing (59) interposed between said tube (57) and said pressure-protecting housing (61) surrounding said digital computing device.