Electricity: measuring and testing – Magnetic – Fluid material examination
Reexamination Certificate
1998-12-23
2001-06-12
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Fluid material examination
C324S201000, C073S025020
Reexamination Certificate
active
06246227
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus for the measurement of the quantity of oxygen, or other relatively strong paramagnetic gas, in a gaseous mixture by use of its magnetic susceptibility through its effect on the induced motion of a test body in a magnetic field.
2. The Prior Art
The measurement of oxygen via its paramagnetic susceptibility has been known since the middle of the 19
th
century when Faraday showed that all materials interacted with a magnetic field. Gases were found in general to be repelled by a magnetic field and we described as being diamagnetic, whilst oxygen and some other gases were found to be attracted to a magnetic field and called paramagnetic. The very high paramagnetism of oxygen enabled its measurement by magnetic susceptibility techniques.
Two principal methods were originally developed for implementation of this technique. One was to employ a uniform magnetic field whilst the other employed the non-uniform field as originally described by Faraday. An example of the former technique is given by L. G. Gouy in Compt. Rend. Vol. 109 (1885) 935 while an example of the latter is given by P. W. Selwood in Magnetometry 2nd Edition, 1993, Interscience N/Y London 1956. The bulky and delicate nature of these instruments led to the development of further apparatus amongst which the most successful were those based on the original Faraday gas susceptibility balance. In these designs a test body of well defined shape is suspended inside a gas cell. The test body is made of materials, such as quartz, which have a low value of diamagnetic susceptibility and is suspended such that a strong non-uniform magnetic field is present across it. When the paramagnetic gas enters the test cell the gas tends to move to congregate at the point of strongest magnetic field causing a change in the position of the test body which can be measured and related to the concentration of paramagnetic gas in the cell.
Several forms of test body have been investigated including the commonly used dumbbell (e.g. G. C. Haven, Physical Review Vol. 41 (1932) 337) and also with modifications using a flattened structure (e.g. U.S. Pat. No. 3,815,018). Some other patents using dumbbell based designs for Faraday balances include U.S. Pat. No. 2,416,344 and U.S. Pat. No. 2,962,656. The apparatus described by these and other patents are similar in that all of them employ an optical method to detect the rotation of the dumbbell as the magnetic nature of the gas in the test cell is altered. Although in some cases a feedback system was employed in order to produce a null balance system, by electromagnetism, by electrostatic means (U.S. Pat. No. 3,026,472) and by variation of the magnetic field (U.S. Pat. No. 3,879,658) all of these techniques still required the use of optical means to provide the final measurement.
Non optical detection systems have also been disclosed that employ extra components to detect the rotation of the test body. These include the use of magneto-resistive pickup (GB-A-1 220 413), employment of separate high frequency excitation and pickup coils (U.S. Pat. No. 3,714,557), and capacitive sensing of the rotation, (U.S. Pat. No. 3,612,991). In these cases the use of an optical detection method has been replaced by the use of an alternative but in each case the new measurement technique is an additional system to the basic susceptibility balance and acts as an alternative to the optics.
WO92/05436 described an alternative arrangement for the measurement of the proportion of a paramagnetic gas not requiring the additional detection system extra to the basic susceptibility balance. In particular, it proposed that a test element should be made to vibrate in a varying magnetic field by the application of a current through the test element and where the electrical conductors used to apply the current to cause the current to cause oscillation were also used to sense the subsequent oscillation of the elements in the magnetic field. As described in that document, certain parameters of the oscillation, such as damping and frequency, are dependent on the proportion of the paramagnetic gas in the cell and therefore this proportion can be determined from measurements of the ongoing oscillation.
SUMMARY OF THE INVENTION
The present invention provides apparatus for the measurement of the proportion of paramagnetic gas in a gas mixture comprising a chamber to which said gas mixture may be admitted, means arrange to generate, within such chamber, a gradient magnetic field, a test element and means arranged to mount said test element in said gradient magnetic field such that the test element may rotationally oscillate about an axis, wherein said mounting means comprises electrical conductor means arranged to carry current to and from said test element whereby current may be applied to said test element to cause oscillation thereof and whereby EMF generated by movement of the test element in said gradient magnetic field may be measured.
The present invention therefore advantageously provides a gas sensor cell of simple construction in that there is no need to provide additional sensing elements to monitor the movement of the test element. This is because the same conductors which pass the current to cause the oscillation of the test element are used as the input to a sensing means which, by way of the generated EMF, can determine the characteristics of the oscillation of the element. From the variation in these characteristics the proportion of paramagnetic gas in the cell may be determined.
The present invention therefore utilizes principles set out in WO 92/05436, but has the advantage of using, in the preferred embodiment, well known gas sensor elements in its construction and also the number of degrees of freedom of movement of the test element is limited which considerably simplifies the required driving and sensing circuitry.
REFERENCES:
patent: 2744234 (1956-05-01), Munday et al.
patent: 3815018 (1974-06-01), Gast et al.
patent: 3826974 (1974-07-01), Kocache et al.
patent: 4983913 (1991-01-01), Krause et al.
patent: 5369980 (1994-12-01), Kocache
patent: 5932794 (1999-08-01), Fabinski et al.
patent: 1 220 413 (1971-01-01), None
International Publication No. WO 92/05436, dated Apr. 2, 1992, by Riad Kocache.
Hobby James
Holman Danny
Kocache Riad Mouhamed Adel
Dykema Gossett PLLC
Strecker Gerard R.
LandOfFree
Sensor for measuring the magnetic characteristics of a gas does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sensor for measuring the magnetic characteristics of a gas, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensor for measuring the magnetic characteristics of a gas will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2511777