Method and apparatus for magnetically detecting defects in an object with compensation for magnetic field shift by means of a compensating coil
US5512821A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 1, 1993 |
| Grant date | Apr 30, 1996 |
| Priority date | — |
| Expiry date | Feb 1, 2013 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N27/82
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A magnetic detector includes a magnetizer generating a magnetic field; a first magnetic sensor for detecting a leakage flux resulting from a magnetically defective portion of an object moving in and relative to the magnetic field; a low-pass filter for extracting a low-frequency signal component contained in the signal output by the magnetic sensor, the low-frequency signal component being indicative of a floating flux which crosses the magnetic sensor and is a result of the object moving through the magnetic field; an amplifier for amplifying the extracted low-frequency signal component; a compensating coil excited by the amplified low-frequency signal component output by the amplifier, for generating a magnetic flux which cancels out the floating flux crossing the magnetic sensor; a high-pass filter for extracting a signal resulting from the magnetically defective portion and contained in the signal that is output by the first magnetic sensor; an output amplifier for amplifying a signal output by the high-pass filter to produce a defect signal; a second magnetic sensor located near the first magnetic sensor, for detecting a component of the magnetic field which is parallel to the…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.