Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1986-12-16
1989-06-06
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324327, 324204, G01N 2774, G01R 3312, G01V 308
Patent
active
048375110
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus for detecting metals and is especially but not exclusively suited to monitoring metallic debris in fluids generally and in lubricating oil in particular. In other examples the invention can be made to respond to larger metallic items such as coins.
In many engineering applications, moving parts in contact with each other must be lubricated. Despite the efficiency of the lubrication method employed, over a period of time, wear inevitably occurs. The result is that small particles of the material from which the parts concerned are made are released and carried away in the moving oil. It follows that measurement of the levels and type of particulate contamination in a lubricating oil can be used as an indicator of the mechanical condition of the equipment.
While it is a relatively simple task to perform off-line analysis of oil samples, continuous monitoring of an oil in situ presents a more difficult problem, requiring appropriate transducer systems measuring an appropriate property which changes with the build up of contamination of the oil.
One form of apparatus which has been proposed for the continuous monitoring cf particulate contamination of lubricating oil is described in British Patent Specification No. 1 348 881 and uses a bridge circuit to sense the differential changes in impedance of two coils magnetically coupled to the flowing oil due to particles carried along by the oil. British Patent Specification No. 1 510 103 and British Patent Application No. 2 004 374A utilize the change in resonant frequency of a tuned circuit due to the passage of a metallic particle through the inductor of the circuit to provide an indication of the presence of the particle.
It is also known from British Patent Specification No. 1 510 103 that ferromagnetic, electrically conductive and electrically resistive particles produce different effects on the inductance of a coil when they are magnetically coupled to it.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for detecting metal items and producing an indication of the metal of which the item is composed.
According to one aspect of the present invention there is provided a method of detecting metal items moving along a predetermined path, providing an oscillator having a resonant circuit including a capacitor and an inductor, the oscillator being such that the frequency of its oscillation is dependent on the inductance of the inductor and the amplitude of the oscillation is dependent on the resistive loading on the inductor, magnetically coupling the inductor to the predetermined path so that any metal item moving along it would be coupled to the inductor, measuring the changes in the frequency and the amplitude of the oscillation due to the passage of the item along the path, and providing an output indication characteristic of the metal of the item moving along the predetermined path.
According to a second aspect of the present invention there is provided apparatus for detecting metal items moving along a predetermined path including an oscillator having a resonant circuit including a capacitor and an inductor, the oscillator being such that the frequency of its oscillation is dependent on the inductance of the inductor and the amplitude of its oscillation is dependent on the resistive loading on the inductor, and the inductor being magnetically coupled to the predetermined path, first means for measuring changes in the frequency of the oscillation produced by the oscillator, second means for measuring changes in the amplitude of the oscillation produced by the oscillator, and output means responsive to the first means and second means to produce an output indication characteristic of the metal of the item moving along the predetermined path.
The metal items could be particles in a flow of fluid, such as lubricating oil, a coolant fluid, a slurry e.g. of wood pulp, or smoke. Alternatively, the metal items could be coins in a coin
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Flanagan Ian
Jordan James R.
Whittington Herbert W.
Edmonds Warren S.
Eisenzopf Reinhard J.
Ranco Europe Limited
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