Eddy current inspection tool which is selectively operable in a discontinuity detection mode and a discontinuity magnitude mode

• US 4,412,177 A
• Filed: 10/29/1980
• Issued: 10/25/1983
• Est. Priority Date: 10/29/1980
• Status: Expired due to Term

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Petrini, Richard R., Van Lue, Dorin F.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/201,946
• Time in Patent Office: 1,091 Days
• Field of Search: 324/207, 324/208, 324/219-221, 324/226, 324/227, 324/234, 324/236-240, 324/327, 324/329, 350/96.26
• US Class Current: 324/226
• CPC Class Codes: G01N 27/902 by moving the sensors
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat
• CPC Class Codes: G02B 23/26 using light guides for illumination G02B23/2469

Abstract

A miniaturized inspection tool, for testing and inspection of metal objects in locations with difficult accessibility, which comprises eddy current sensing equipment (12) with a probe coil (11), and associated coaxial coil cable (13), coil energizing means (21), and circuit means (21, 12) responsive to impedance changes in the coil as effected by induced eddy currents in a test object to produce a data output signal proportional to such changes. The coil and cable are slideably received in the utility channel of the flexible insertion tube 17 of fiberoptic scope 10. The scope 10 is provided with light transmitting and receiving fiberoptics for viewing through the flexible tube, and articulation means (19, 20) for articulating the distal end of the tube and permitting close control of coil placement relative to a test object. The eddy current sensing equipment includes a tone generator 30 for generating audibly signals responsive to the data output signal. In one selected mode of operation, the tone generator responsive to the output signal above a selected level generates a constant single frequency tone for signalling detection of a discontinuity and, in a second selected mode, generates a tone whose frequency is proportional to the difference between the output signal and a predetermined selected threshold level.

Claims

1. An eddy current inspection tool for nondestructive testing and detection of discontinuities in metal objects, said tool comprising:

an eddy current sensing coil;

means for activating said coil with a high-frequency signal whereby said coil is adapted to induce eddy currents in objects positioned within the pulsating magnetic field of said coil;

circuit means responsive to impedance changes produced in said coil by the eddy currents induced in the test object, to produce a voltage output data signal which is proportional to the distance between said coil and the test object; and

audio signalling means, operable in at least two modes and responsive to said voltage output data signal, for audibly signalling the detection of a discontinuity in the test object, which audio signalling means includes a mode select switch which is selectively operable in a first mode to route said voltage output data signal through means responsive to said voltage output data signal for generating a constant single frequency tone indicating detection of a discontinuity in said test object, and which mode select switch is selectively operable in a second mode to route said voltage output data signal through means responsive to said voltage output data signal for generating from a tone generator means a signal tone whose frequency is proportional to the voltage output data signal whereby said signal tone is indicative of the magnitude of the discontinuity in inspection applications or of the degree of displacement of the test object in displacement measurement applications.

2. An eddy current inspection tool for nondestructive testing and inspection of metal objects, said tool comprising:

a miniaturized test coil;

means for activating said coil with a high frequency electrical signal, whereby said coil is adapted to produce eddy currents in metal objects positioned within the pulsating magnetic field of said coil, said means including a coaxial cable electrically coupling said test coil to said activating means, with said coil being located at the free end of the cable and having a diameter substantially equal to the diameter of said cable, and of a size whereby said coil and coaxial cable can be slideably extended through the utility channel of a fiber optic scope;

circuit means which include said test coil, which is electrically connected in series to an impedance bridge means, which is in turn electrically connected in series of a signal conditioner means, said circuit means being responsive to impedance changes produced in said coil by eddy current induced in the test objects, to produce as an output from said signal conditioner means a voltage output data signal which is proportional to said impedance change; and

audio signalling means responsive to said voltage output data signal, for audibly signalling the detection of a discontinuity in the test object, said audio signalling means including a tone generator means for producing the audible signal, a comparator amplifier means electrically connected to said tone generator and which in response to said voltage output data signal produces as an output a constant frequency signal, and an amplifier means electrically connected to said tone generator means and which in response to said voltage output data signal produces as an output a variable frequency signal; and

a mode select switch, electrically connected to said audio signalling means to selectively route said constant and variable frequency signals, wherein said mode select switch is selectively operable in a first mode (the "chirp mode") to route said constant frequency signal through means responsive to said constant frequency signal for generating a constant single frequency tone for indicating detection of a discontinuity in said test object or its displacement, and wherein said mode select switch is selectively operable in a second mode (the "feedback scan mode") to combine and route said constant and variable frequency signals emerging from said comparator amplifier means and said amplifier means to means responsive to said frequency signals for generating a signal tone whose frequency is proportional to the voltage of the voltage output data signal.

3. An eddy current sensing tool as described in claim 2, wherein said audio signalling means is provided with a predetermined threshold voltage such that, in either mode of operation said audio signalling means is responsive to said voltage output data signal only when said voltge output data signal exceeds said predetermined threshold voltage, and the frequency of the audible tone generated by said audio signalling means in the second mode (the "feedback scan mode") is proportional to the difference between said voltage output data signal voltage and said threshold voltage.