Electricity: measuring and testing – Magnetic – Displacement
Patent
1994-07-20
1996-06-11
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Displacement
32420716, 32420719, 324233, 364573, G01B 714, G06G 728
Patent
active
055259006
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and an apparatus for determining the displacement of an object of an electrically conducting material.
When measuring displacement with eddy current proximity probes or transducers, the precision of the transducers is limited by their sensitivity to changes within three essential parameters of the object to be measured, which are conductivity, permeability and temperature. The changes in conductivity and/or permeability may be due to the material of the measured object being non-homogenous and/or due to changes in the temperature. Usually, displacement transducers are calibrated for a certain material, and if this material is non-homogenous the measured displacement value will be erroneous.
In the article "Principles of eddy-current distance gauges", Prof. H. Sutcliffe, PROC. IEE, Vol. 124, No 5, May 1977, the field theory of an a.c. loop over a metal surface is reviewed and expressions are derived which demonstrates the possibility of a method of distance gauging in which the effect of conductivity and permeability of the metal can be compensated. In the method of Sutcliffe, a high frequency primary current I is supplied to a probe coil and it is discussed that the measured electromagnetic field V can be divided into three components, V.sub.1, V.sub.2 and .DELTA.V. V.sub.1 is the voltage that would be induced by the primary current I in the absence of the metal, where V.sub.1 leads I by 90.degree., V.sub.2 is the voltage that would be induced by an ideal mirror image of the probe coil and lags I by 90.degree., and the third component of the voltage .DELTA.V is a function of the conductivity and the permeability of the metal besides being a function of different parameters of the probe. It is however concluded that over a wide range of conditions .DELTA.V leads I by a phase angle of 45.degree.. Thus a distance gauge system is proposed by Sutcliffe in which the effect of .DELTA.V is compensated for by introducing a load impedance with a -45.degree. phase angle, and thus compensating for the effect of conductivity and permeability of the metal.
However, the assumption of the 45.degree. phase angle is only valid for restricted values of operating parameters and the system proposed by Sutcliffe does not provide a general solution to the problem of compensating for changes in the condutivity and the permeability of the object of measurement when measuring displacement of an object of an electrically conducting material. Furthermore, it is to be noted that the system proposed by Sutcliffe is not suitable for use in connection with objects of measurement having a coating of an electrical conducting material.
An example of an eddy current transducer for measurement of material thickness is disclosed in SU-A-1223129. This patent discloses a transducer in which changes of electroconductivity of the measured object are compensated for by the use of a compensation winding which is set at a distance from the operating surface.
An eddy current proximity detection system is disclosed in U.S. Pat. No. 4,875,007. This patent discloses a detection system in which the effects of changes in temperature are reduced. To compensate for a decrease in probe sensitivity with temperature, a temperature sensitive element is included in a network which controls the amplitude of an oscillator, which is alternately feeding two matched probes, one a measurement and the other a reference probe. In this system the probes are operated in a resonant mode to increase both the system linearity and sensitivity.
It is an object of the present invention to provide a method and a system for determining the displacement of an object of an electrically conducting material wherein the effects of variations in the parameters of the material such as conductivity and permeability may be compensated for.
Another object of the present invention is to provide a transducer system in which the effects of changes in temperature are reduced.
A further object of the invention is to provide a system for linearization of
REFERENCES:
patent: 3586964 (1971-06-01), Strouch
patent: 3636338 (1972-01-01), Abnett et al.
patent: 4095469 (1978-06-01), Yamada et al.
patent: 4837510 (1989-06-01), Tornblom
patent: 4864235 (1989-09-01), Tornblom
patent: 4875007 (1989-10-01), Ginns
patent: 4950987 (1990-08-01), Vranish et al.
patent: 5003262 (1991-03-01), Egner et al.
patent: 5027066 (1991-06-01), Reder
patent: 5130651 (1992-07-01), Morrey, Jr.
"Image of a Coil in Relation to the Gauging of Distance of Metal Surfaces"; Electronics Letters; Oct. 3, 1974; vol. 10; No. 20; pp. 409-410.
"Principles of Eddy-Current Distance Gauges"; Prof. H. Sutcliffe; Proc. IEE. vol. 124, No. 5; May 1977; pp. 479-484.
Jensen Henrik B.
Larsen Gunner H.
A/S Bruel & Kjaer
Strecker Gerard R.
LandOfFree
Method for determining the displacement of an object of an elect does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for determining the displacement of an object of an elect, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for determining the displacement of an object of an elect will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-354304