US 3,940,690 A · Multi-probe flux leakage testing apparatus using skewed probes

Abstract

In apparatus in which an object moves longitudinally and rotationally with respect to a multi-probe assembly, each probe including a channel-shaped core of magnetic material having spaced sides which are long compared to the thickness thereof and a coil encircling the core, and bipolar signals are developed whose positive and negative excursions correspond to the largest flaw signal of each polarity simultaneously occurring in the probes, the probes of the assembly are arranged in succession along the longitudinal path of travel of the object and skewed with respect to the longitudinal path of travel with an end of one probe adjacent the end of the next probe to yield flaw indications for longitudinal defects which are largely dependent on the depth of the flaw and independent of its length. Accordingly such indications are approximately the same as for short defects of the same depth, thereby yielding indications more nearly corresponding to the severity of the defects. Two or more probe assemblies with the same skew direction may be employed to increase the speed of inspection. If helical flaws of opposite pitch can be present, two probe assemblies of opposite skew directions can be employed.

Claims10

Dependent claims

Multi-probe flux leakage testing apparatus for detecting flaws in an object relatively moving longitudinally and rotationally with respect to the probes which comprises

a. means for producing a steady state magnetic field in said object in the test region thereof,
b. a plurality of leakage-flux probes for producing respective signal outputs having positive and negative excursions corresponding to flaws passing thereby in said test region,
c. said probes each including a channel-shaped core of magnetic material of generally U-shaped cross-section and having spaced sides which are long compared to the thickness thereof and a coil encircling the core for producing said signal outputs,
d. said probes being arranged in succession along the longitudinal path of travel of a said object and skewed with respect to said longitudinal path of travel with an end of one probe adjacent an end of the next probe respectively,
e. means for rectifying and combining the positive portions of the signals from said probes and rectifying and combining the negative portions of the signals from said probes to yield positive and negative signals corresponding to the largest signal of each polarity simultaneously occurring in said probes,
f. adding means for adding said largest positive and negative signals to yield bipolar signals having corresponding positive and negative excursions,
g. and circuit means responsive to said bipolar signals for indicating flaws in a said object.

4 more elements

Multi-probe flux leakage testing apparatus for detecting flaws in an object relatively moving longitudinally and rotationally with respect to the probes which comprises

a. means for producing a steady state magnetic field in said object in the test region thereof,
b. a plurality of leakage-flux probes for producing respective signal outputs having positive and negative excursions corresponding to flaws passing thereby in said test region,
c. said probes each including a channel-shaped core of magnetic material of generally U-shaped cross-section and having spaced sides which are long compared to the thickness thereof and a coil encircling the core for producing said signal outputs,
d. said probes being symmetrically arranged in succession along a line parallel to the longitudinal path of travel of a said object and skewed with respect to said line with a side of one core in alignment along the skew angle with a side of the next core and with adjacent ends abutting, the other sides of the respective cores being on opposite sides of the aligned sides,
e. means for rectifying and combining the positive portions of the signals from said probes and rectifying and combining the negative portions of the signals from said probes to yield positive and negative signals corresponding to the largest signal of each polarity simultaneously occurring in said probes,
f. adding means for adding said largest positive and negative signals to yield bipolar signals having corresponding positive and negative excursions,
g. and circuit means responsive to said bipolar signals for indicating flaws in a said object.

4 more elements

Dependencies are inferred from the claim text.

Multi-probe flux leakage testing apparatus using skewed probes

Life of this patent

Multi-probe flux leakage testing apparatus using skewed probes

Life of this patent

Abstract

Claims10