Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/06—Investigating concentration of particle suspensions
  • G01N15/0656—Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/12—Measuring magnetic properties of articles or specimens of solids or fluids

Definitions

• a High Resolution Magnetometer This invention relates to a magnetometer whose purpose is to measure such parameters as the total mass, volume and magnetic or electric properties such as permeability, magnetic moments, Curie temperatures, etc., of a sample particle or particles.
• Existing magnetometers usually rely on oscillating samples in a strong magnetic field, and consequently have problems arising from the feedback of mechanical vibration, pick ⁇ up of mains frequency and other inherent problems.
• Present magnetometers are primarily used in connection with laboratory techniques, and not easily transportable or lack the sensitivity and adaptability that may be required.
• an electro magnetic device for sensing or measuring metallic samples of material, the device comprising one or more transducers, consisting of an excitation coil for creating an alternating gradient magnetic field in the gap between the coil and the limb or limbs of a path defined by a body of magnetically permeable material, a detector coil positioned in the gap of the path, means for positioning a sample adjacent to the detector coil of one transducer and reading means for indicating any changes to the output of the transducer due to the positioning of a sample adjacent to the detector coil and/or for comparing in opposition the outputs from two such transducers.
• transducers consisting of an excitation coil for creating an alternating gradient magnetic field in the gap between the coil and the limb or limbs of a path defined by a body of magnetically permeable material, a detector coil positioned in the gap of the path, means for positioning a sample adjacent to the detector coil of one transducer and reading means for indicating any changes to the output of the transducer due to the positioning of a sample adjacent to the
• One application for the present device is that of condition monitoring, whereby the analysis of metal particles, worn from moving parts in machines, in terms of type of metal, size and total mass, may give an insight into the present and future wear patterns.
• a sample may be subjected to measuring by positioning it in proximity to the sensing area of one of a pair of inductive transducers.
• the two transducers form a balanced, differential pair of elements in such a manner that when no particles are present their electromagnetic signal outputs are of equal or near equal magnitude, and of opposite polarity.
• An alternating magnetic field is created by an alternating current in the excitation coil and this is situated within the permeable limb so that the lines of force are largely contained within the path, except for a relatively short air gap. It is into this air gap that the pick-up coil is positioned so that the electromotive force (emf) is induced in it by the alternating field.
• emf electromotive force
• the operating frequency of the magnetic field, the intensity of the field, the permeability of the magnetic limbed path, as well as the properties of the particles are all related to the differential signal.
• the difference signal output is then electronically processed.
• the difference signal is amplified by an initial amplifier, the output of which is then passed through a series of further amplifiers which constitute band pass filters, so that only the desired signal or signals is transmitted.
• a detector stage follows which may consist of an analogue AC to DC converter which can drive an analogue meter or a digital panel meter. In these a reference signal may be taken from an amplitude detector monitoring the amplitude of oscillation of the field in the excitation coils.
• the difference voltage signal should be exactly zero before a sample is placed in position so as to facilitate the accurate measurement of the sample's parameters.
• This zeroing of the apparatus is achieved by exactly matching e fs induced in the two detector coils so that at the mixer stage they cancel out.
• the first method is to adjust one or possibly both resistors placed in series with the two detector coils and the mixer stage, and so alter the relative signals until equality is obtained between them.
• a second method involves altering the position of two small masses, one of non-ferrous, and the one of ferrous metal, in relation to one of the detector coils, so as to induce a small balance restoring emf. These methods may be used independently or together.
• Figure 1 illustrates, in cross-section, a transducer for a sample measuring device of this invention
• Figures 1A, IB and 1C are alternative embodiments of the transducer, in cross-section
• Figures ID and IE are, respectively, plan views of the transducers of Figures lAand IB and of Figure 1C;
• Figures IF and 1G are cross-sectional and plan views respectively of a further embodiment of a transducer of this invention.
• Figures 2A and 2B illustrate alternative methods of use of a dual transducer system of a measuring device of the invention
• Figure 3 illustrates excitation or detection circuitry for use with the device of Figure 2;
• Figures 4 and 5 show in cross-section and plan view two proposed types of sample collecting cell for use with the measuring device shown in previous drawings;
• Figures 6 and 7 are side and plan views of a further type of sample collecting cell; and
• FIGS 8 and 9 illustrate two still further possible types of sample collecting cell.
• Figure 1 illustrates a transducer wherein an annular detector coil 3 is shown arranged co-axially above an excitation coil 4. An alternating magnetic field is created in a low reluctance magnetic path 5 by means of an alternating current in the drive coil 4.
• the detector coil is positioned in such a way that it is influenced by a strong gradient magnetic field between the centre pole and the peripheral pole or poles of the magnetic path, with the result that the detector coil has an emf induced in it.
• Introduction of a sample 6 of particles in the position illustrated causes a local realignment of the magnetic field and hence a change in the emf induced in the detector coil 3.
• Figures 1A to 1G illustrate a number of possible variations in the design of the transducer.
• the geometry of the permeable limb pole is similar to that of Figure 1.
• the outer low reluctance limb 5 varies from one example to another giving a variation of the magnetic field pattern, providing flexibility of design for particle measurement instruments where the particles are distributed in various ways on substrates.
• the e fs from the two detector coils of a pair of transducers 1,2 are compared or mixed in opposition. When no sample is present the voltage signals at the mixing point should be equal and of opposite polarity to cancel exactly.
• two masses 8, one of non-ferrous and the other of ferrous etal are adjusted in relation to one of the transducers so as to change the emf induced within the detector coils.
• Adjustable resistors 9A and 9B can also be used to adjust the voltage signals from the two transducers and so zero the mixing point.
• a sample can be positioned as shown and the differential voltage signal is taken as being proportional to the parameter of the sample.
• the difference signal is electronically processed and filtered by a main amplifier 7 and a series of further amplifiers constituting band-pass filters and leading to. a detector and a signal display unit, as shown in Figures 2 and 3.
• Figure 3 shows a. sinusoidal drive device 10 required to provide the excitation field in transducers 1 and 2.
• Figure 2A illustrates a procedure whereby particles are located in one place 6A, relative to one of the transducers 1, in which condition a reading from the magnetometer is taken. The particles are then moved up to a second position 6B from which a second reading from the magnetometer is taken. The difference between the two readings is computed by the circuit of Figures 2A and 3.
• Figure 2B illustrates a different procedure wherein the • particles are located initially at 6A around the vertical axis of the transducer 1 and a reading is taken from the magnetometer. The particles are then taken to a second position 6B on the axis of transducer 2 when a second reading from the magnetometer is taken. The difference in the two readings is then computed by the circuit of Figures 2B and 3. The results achieved by the method of Figure 2B is twice the amplitude of that achieved when using the circuit of Figure 2A.
• Figure 4 indicates a filter capsule made of non- metallic and non-conductive components. Fluid flows into an inlet 13 and out through an outlet 14. A fine filter 15 of porous membrane of paper or of some other material is provided, together with a perforated support plate 16. A known amount of fluid is passed through the capsule. Metal particles 17 are thereby trapped by the filter 15 and are collected in a flat container 11. A removable cover 12 allows for cleaning after use.
• Figure 5 indicates a filter capsule wherein a fluid containing particles flows via inlet 22 and outlet 23 through a container 21. The particles are separated and trapped by an external magnetic or electric field source represented at 24. A predetermined amount of fluid, is passed through- the container 21 and the magnetic field causes the particles to be trapped therein. When the external magnetic field is removed the particles may be measured by the magnetometer.
• the capsule may be cleaned and made ready for re-use by pumping a flushing fluid through the capsule.
• the filter capsules of Figures 4 and 5 may be used in conjunction with the methods of metal particle measurement described in connection with Figures 2A and 2B.
• either of the filter capsules of Figures 4 and 5 may be attached to or built into a movable carrier for ease of movement in relation to the transducers, as shown in Figures 6 and 7, Figure 8 or Figure 9. This method may be used for the method of inline fluid flow particle measurement.

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• Condensed Matter Physics & Semiconductors (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

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• 1987
  • 1987-08-24 WO PCT/GB1987/000594 patent/WO1989002083A1/en not_active Application Discontinuation
  • 1987-08-24 EP EP87905263A patent/EP0377555A1/de not_active Withdrawn
  • 1987-08-24 JP JP62504907A patent/JPH02504669A/ja active Pending

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