Apparatus for measuring the proportion of paramagnetic substances in cancelling a mixture of substances and including a compensating device for cancelling an unwanted signal

• US 5,493,215 A
• Filed: 02/28/1994
• Issued: 02/20/1996
• Est. Priority Date: 02/27/1993
• Status: Expired due to Fees

• Current Assignee: Dragerwerk AG
• Original Assignee: Dragerwerk AG
• Inventors: Otten, Johann
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): Patidar, Jay M.
• Application Number:
  US08/203,042
• Time in Patent Office: 722 Days
• Field of Search: 324/204, 324/225, 324/228, 324/262, 73/25.02, 310/155, 310/168, 310/268, 310/261
• US Class Current: 324/204
• CPC Class Codes: G01N 27/74 of fluids G01N24/00 takes precedence

Abstract

An apparatus for determining the paramagnetic characteristics of substances such as oxygen includes a cuvette rotating in a magnetic field. The cuvette includes measuring chambers and reference chambers and an alternating voltage is induced in the measuring field coils by the rotation of the cuvette along the magnetic field. A base signal disturbing the measuring signal is also generated. This base signal is caused primarily by changes in the thickness of the material in the reference chambers and the measuring chambers and/or by material thickness changes of the cuvette. To eliminate this base signal, the cuvette includes a magnetic compensating device. This device is mounted at such a position that it generates a compensating magnetic field during its rotation through the magnetic field. This compensating field generates a compensating voltage which has the same amplitude as the base signal but has a signal waveform which is opposite in phase to the base signal.

Claims

1. An apparatus for measuring the proportion of a paramagnetic substance such as oxygen in a mixture of substances, the apparatus comprising:

a housing defining a longitudinal axis and having a first longitudinal end and a second longitudinal end opposite said first longitudinal end;

a cuvette disposed between said longitudinal ends and having a measuring chamber filled with said paramagnetic substance and a reference region containing a reference material;

magnetic field means for generating a magnetic field;

drive means for rotating said cuvette in said magnetic field so as to cause said magnetic field to alternately penetrate said measuring chamber and said reference region to produce a magnetic alternating field because of different magnetic fluxes in respective ones of said chamber and said reference region;

measuring field coil means mounted in said housing adjacent said cuvette and being subjected to said magnetic alternating field wherein an inductive alternating voltage signal is induced in said measuring field coil means;

said voltage signal being a composite signal defining an index for the concentration of said paramagnetic substance in said measuring chamber;

said composite signal including a measuring signal component caused by said measuring chamber and a reference signal component caused by said reference region;

said measuring chamber and said reference region having respective different material thickness wherein an unwanted base signal is generated in said measuring field coil means;

said cuvette defining a rotational plane and having a magnetic compensating device mounted thereon in said rotational plane;

said magnetic compensating device including an induction loop made of electrically conductive material and said induction loop having a terminating resistor so that a current is produced in said induction loop in dependence upon the magnetic of said field thereby, in turn, generating a compensating field; and

,

said induction loop being mounted at a predetermined location on said cuvette whereat said induction loop generates, via said compensating field, a compensation voltage in said measuring field coil means during the rotation of said cuvette with said compensation voltage having the same amplitude as said unwanted base signal but having a waveform opposite in phase thereto.

2. The apparatus of claim 1, said cuvette having a surface parallel to said rotational plane;

and, said induction loop being mounted on said surface of said cuvette so as to extend radially outwardly.

3. The apparatus of claim 2, said drive means defining an axis of rotation about which said cuvette is rotated;

said cuvette being a circular disc made of diamagnetic material and said measuring chamber being a first cutout formed in said circular disc for receiving a throughflow of said paramagnetic substance therein;

said circular disc having a second cutout formed therein for likewise receiving a throughflow of said paramagnetic substance;

said first and second cutouts being rotationally symmetrical with respect to said axis of rotation;

said cutouts conjointly defining an angle therebetween; and

, said loop being placed at such an angular position after one of said cutouts so that said angular position corresponds to a fourth part of said angle between said cutouts.

4. The apparatus of claim 3, said drive means defining an axis of rotation;

said cutouts lying on an imaginary circle concentric to said axis of rotation; and

, said cutouts being configured as annular slot segments extending along respective segments of said imaginary circle.

5. The apparatus of claim 3, said cutouts being configured so as to have a kidney-shaped contour concentric to said axis of rotation.

6. The apparatus of claim 1, said drive means defining an axis of rotation about which said cuvette is rotated;

said cuvette having a surface parallel to said rotational plane;

said induction loop being mounted on said surface along a radius on one side of said axis of rotation; and

, said apparatus further comprising a metal platelet mounted on said surface diametrically opposite said induction loop.