Electricity: measuring and testing – Magnetic – With compensation for test variable
Reexamination Certificate
1999-01-29
2001-10-09
Oda, Christine K. (Department: 2862)
Electricity: measuring and testing
Magnetic
With compensation for test variable
C324S238000, C324S240000
Reexamination Certificate
active
06300759
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a test arrangement for inspecting the integrity of concrete parts such as, for example the prestressing steel of prestressed concrete construction elements, with a testing head, which has a magnetization device for generating a magnetic field around the construction element, and with a controller for controlling the magnetization process and for processing the signals corresponding with the magnetic field; as well as to a device for such an inspection.
2. The Prior Art
Fractures of the prestressing reinforcement are detected through characteristic anomalies of the magnetic field surrounding the construction element. Such anomalies are based on local variations of the magnetization, or of the magnetic permeability of the prestressing reinforcement. The magnetic field is measured in the course of the magnetization process (measurement in the active field), or after the magnetization process (measurement of the residual field). The problem with the evaluation of the magnetic stray field signals lies in the fact that fracture signals, if any, are superimposed by the signals of the slack reinforcement near the surface.
The test arrangement and the method of magnetic stray field measurement have been employed for some time now for non-invasive inspection of the integrity of the prestressing reinforcement of concrete construction elements. The stray field signals are primarily influenced by the cross girders. Since the construction element is tested from the surface bia a testing head, the spacing of the cross girders from the testing head is smaller than the spacing of the prestressing reinforcement from the testing head. The amplitudes of the girders signals are consequently higher than the emplitudes of the fracture signals—if any—in most cases.
When measuring in the active field, fractures of the pre-stressing reinforcement can be detected by the method of measuring at different magnetization field intensities. Use is made in this connection of the saturation behavior of ferromagnetic materials; the reinforcement near the surface reaches magnetic saturation earlier than the reinforcement located in deeper zones.
Fracture detection thus takes place by this method through the comparison of signals (correlation analysis; weighted signal difference) of measurements that were carried out at different magnetization field intensities. However, the measuring signal still always contains here the signals of the cross girders.
For suppressing the girder signals in residual field measurements, the cross girders are demagnetized with test arrangements and methods of the state of the art by controlling the magnetization process in numerous steps in a manner not described in detail, so that only the signals of a longitudinal reinforcement or prestressing reinforcement will be left. However, it is possible here too that the longitudinal reinforcement is at least partly demagnetized as well, and that possible fracture signals are therefore not detected.
SUMMARY OF THE INVENTION
Therefore, the problem of the present invention is to provide a test arrangement and a method by which the signals of the cross girders can be eliminated by way of calculation without having to carry out any active demagnetization of the construction element.
The problem is solved in that the testing head magnetizes the construction element over a predetermined measurement section in two successive magnetization operations with opposite polarities, and that the controller switches off the magnetization device after a magnetization process with one polarity is completed, and stores and processes the signals recorded over the measurement section after the magnetization device has been switched off.
The advantage offered by the test arrangement and the method as defined by the invention as compared to active demagnetization of the cross girders (for example through application of counter fields, or alternating magnetic fields) according to the state of the art is that the pole intensity “P” of the magnetization device may remain constant in the magnetization process. This omits costly controlling of the pole intensity of the magnetization device during demagnetization of the girders, which, under certain circumstances, may influence also the magnetization of the longitudinal reinforcement and particularly of the prestressing reinforcement. On the other hand, only two magnetization operations are required as compared to the state of the art described above. This means that the inspection expenditure can be substantially reduced.
A further advantage consists in that the testing head can move with the magnetization device along the construction element to be inspected, whereby the magnetic field of said magnetization device can be described in first approximation by the field of a yoke magnet.
A further advantage consists in that the testing head is arranged in such a way that it is displaceable in directions opposing each other at least partially in order to generate in this way in the construction element magnetizations with different polarities.
A further advantage consists in that the controller superimposes the signals of the magnetization with different polarities by way of calculation, which cancels the signals of the cross girders.
REFERENCES:
patent: 4503393 (1985-03-01), Moyer et al.
patent: 4573013 (1986-02-01), Kusenberger et al.
patent: 4739273 (1988-04-01), Petersen et al.
patent: 4837509 (1989-06-01), Dodmann et al.
patent: 5545987 (1996-08-01), Schutt et al.
patent: 5720140 (1998-02-01), Bousack et al.
patent: 40 37 992 (1992-06-01), None
Bousack Herbert
Krause Hans-Joachim
Sawade Gottfried
Collard & Roe P.C.
Forschungszentrum Julich GmbH
Oda Christine K.
Zaveri Subhash
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