Electricity: measuring and testing – Magnetic – Magnetic sensor within material
Reexamination Certificate
2000-06-21
2004-07-13
Noland, Thomas P. (Department: 2856)
Electricity: measuring and testing
Magnetic
Magnetic sensor within material
C073S866500
Reexamination Certificate
active
06762602
ABSTRACT:
This application claims Paris Convention priority of DE 199 29 072.5 filed Jun. 25, 1999 the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention concerns a device, e.g. an inspection pig, for inspecting conduits made from ferromagnetic materials, such as pipelines, for faults, cracks, corrosion or the like, comprising at least one pulling element, a supporting structure with variable circumference, disposed on the pulling element, and comprising substantially radially disposed supporting arms pivotable about axes disposed perpendicular to the longitudinal central axis of the pulling element, and several permanent magnets disposed on the circumference of the supporting structure for generating a magnetic field, and also having sensors.
So-called inspection pigs are used for inspecting conduits, in particular for transporting water, oil or gas, comprising inspecting means with inspecting elements or sensors, disposed at the outer circumference for inspecting the state of the conduit walls. The sensors can be of various designs. Conventional sensors are i.a. piezo-electrical, electro-acoustic, and electromagnetic sensors such as Hall, stray flux and eddy current sensors.
Different wall conditions or wall thickness reductions, e.g. due to corrosion etc. provide different signals which can be further processed e.g. in an electronic unit.
Conventional inspection pigs for inspecting conduits of different standard widths, or for introducing the inspection pigs via supply lines into the conduit to be inspected, comprise radially expandable supporting structures disposed on a central pulling element with inspecting elements and/or sensors at their circumference. Such supporting structures have a circumference which can vary in dependence on the inner cross-section of the conduit and comprise e.g. several substantially radially disposed supporting arms pivotable about axes disposed perpendicular to the longitudinal central axis of the pulling element (DE 197 46 510 A1, DE 197 46 511 A1).
EP 0 775 910 A1 describes a device for inspecting ferromagnetic materials, in particular conduits, with a radio frequency current coil which serves, in connection with a magnetic field, for excitation or detection of ultra sound waves, wherein the magnetic field is substantially generated by permanent magnets disposed at the circumference of the conduit. An additional magnet arrangement generates a background magnetic field.
These above mentioned devices, based on an electromagnetic measuring principle, have the disadvantage that the magnetic field of the permanent magnets disposed at the circumference of the supporting structure depends on their lateral separation and on the cross-section of the respective conduit, wherein the density of the magnetic field is higher or the magnetic field strength is higher, the smaller the lateral separation between the permanent magnets or the smaller the cross-section of the respective conduit. Consequently, the measuring sensitivity decreases with increasing cross-section of the respective conduit. Moreover, conduits with varying cross-section do not have comparable measuring results and are subject to differing measurement errors.
It is the underlying purpose of the present invention to avoid these disadvantages in a simple and inexpensive fashion.
SUMMARY OF THE INVENTION
This object is achieved in accordance with the invention by a device of the above mentioned kind in that at least some of the permanent magnets are associated with a further magnet having a variable magnetic field for strengthening and/or weakening the magnetic field generated by the permanent magnet in dependence on the circumference of the supporting structure or in dependence on the lateral separation between the permanent magnets.
In a device in accordance with the invention, the magnetic field generated by the permanent magnets can be strengthened or weakened by changing the direction and/or the strength of the magnetic field of the magnets associated with the permanent magnets. In this fashion a magnetic field with a substantially constant magnetic field strength can be obtained for conduits of any cross-section irrespective of the lateral separation between the permanent magnets. For reasons of symmetry, one magnet with a variable magnetic field is associated with each permanent magnet.
A first variant of the embodiment provides that the magnet with variable magnetic field is also a permanent magnet which can be turned by means of an actuator for changing the direction of its magnetic field. Turning of the poles of the magnets can thereby move same e.g. into a position aligned with the orientation of the poles of the permanent magnets to optimally increase the magnetic field generated by the permanent magnets for inspecting conduits with large standard width. Conversely, the magnetic field generated by the permanent magnets can e.g. be weakened to a maximum extent if the rotatable magnets and their poles are moved to an orientation opposite to the poles of the permanent magnets to weaken the magnetic field generated by the permanent magnet for inspecting a conduit with small standard width. By turning the magnets, their magnetic field lines can be oriented at an arbitrary angle with respect to the field lines of the magnetic fields generated by the permanent magnets to thereby strengthen or weaken same in a variable fashion.
The actuator can comprise at least one toothed wheel engaging the rotatable magnet, which can e.g. be formed as a shaft which is rotatably disposed and connected to such a toothed wheel for secure mutual rotation. In this case, the rotatable magnet also comprises a toothed wheel connected for secure rotation therewith. Alternatively, the rotatable magnet, e.g. of cylindrical shape, has a toothing at its circumference.
In a preferred embodiment, the actuator can be driven electrically. The actuator can be driven e.g. by an electric motor which communicates with at least one sensor element for detecting the circumference of the supporting structure or the lateral separation between the permanent magnets.
In accordance with a further preferred embodiment, the actuator is mechanically driven. Such a purely mechanical drive has, in particular, the advantage that no additional, in particular, electrical driving means are required. It is therefore very inexpensive and no additional drive or current supply means are required for the arrangement.
In a preferred embodiment, the mechanically driven actuator is driven by at least one helical spring which resiliently biases the supporting arms laterally outwardly at the circumference of the supporting structure and, with lateral approach or withdrawal of the supporting arms, converts the length change associated with its compression or expansion, into a rotary motion of the actuator.
A second variant of the embodiment provides that the magnet of variable magnetic field is an electromagnet, e.g. an induction coil, which can be supplied with a variable current to change the magnetic field strength. In this case, the induction coil magnets can be supplied e.g. with an induction current inducing a magnetic field oriented in the direction of the magnetic field of the permanent magnets to increase same for inspecting a conduit with large standard width. Conversely, the magnetic field generated by the permanent magnets can be weakened by supplying an opposite induction current to the induction coil to weaken the magnetic field generated by the permanent magnets for inspecting a conduit with small standard width. The induction coils preferably communicate with at least one sensor element for determining the circumference of the supporting structure or the lateral separation between the permanent magnets for varying the strength and/or direction of the induction current depending on the cross-section of the conduit.
Each permanent magnet at the circumference of the supporting structure preferably has an associated longitudinally disposed further permanent magnet for generating a magnet
Laursen Poul
Meredith Christopher
Noland Thomas P.
PII Pipetronix GmbH
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