Nondestructive, resonant testing apparatus with magnetic pickup

Claim 1

A nondestructive, resonant testing apparatus for detecting faults in castings and the like comprising means for striking a casting to induce vibration thereof, vibration sensing means responsive to vibration of said casting to develop an electrical test signal having frequency and amplitude variations representing the vibration of said casting, frequency discrimination circuit means operatively coupled to said sensing means and responsive to said test signal to develop a first output signal when said test signal has a predetermined frequency within a predetermined frequency range, decay rate detection circuit means operatively coupled to said vibration sensing means to provide a second output signal when the time required for said test signal to decay from a first amplitude to a second amplitude is within predetermined limits, and output circuit means responsive to said output signals to indicate a fault in a casting in response to predetermined deviations in either one of said signals, and wherein said sensing means comprises means producing a magnetic field and pickup means to sense variations in said field and develop said test signal so that when said casting is operatively associated with said field and said pickup means, vibrations induced in said casting cause said field and said test signal to vary in accordance with vibration of said casting, and wherein said decay rate direction circuit means comprises means responsive to said test signal to provide a first timing pulse when said test signal decays to said first amplitude and a second timing pulse when said test signal decays to said second amplitude, first circuit means including a first capacitor, second circuit means including a second capacitor and third circuit means responsive to said first timing pulse and said second timing pulse to vary the charge on said first and said second capacitors in accordance with the time required for said test signal to decay from said first amplitude to said second amplitude, one of said capacitor circuit means being responsive to the charge on its capacitor to indicate when said decay time of said test signal is within said predetermined limits, and the other of said capacitor circuit means being responsive to the charge on its capacitor to indicate when said decay time of said test signal is outside at least one of said predetermined limits.

Claim 5

An apparatus for detecting flaws in a workpiece such as a casting or the like comprising means for generating a magnetic field, magnetic field sensing means mounted in spaced relation to said magnetic field generating means and operatively coupled to said field to develop a test signal in response to variations in said field, said generating means and said sensing means being arranged to receive said casting in the space therebetween with said casting disposed in said field, means for striking said casting to cause said casting to vibrate and to thereby cause Said magnetic field to vary in accordance with vibration of said casting and develop in said sensing means a test signal whose frequency and amplitude represent vibration of said casting, and output circuit means responsive to said test signal and operative to detect deviations in said test signal from a corresponding test signal representing vibration of an acceptable casting, and wherein said striking means and said magnetic field sensing means are disposed at a test station and wherein said apparatus further comprises a conveyor movable through said test station and holder means mounted on said conveyor to accommodate a workpiece thereon, said magnetic field generating means comprising a permanent magnet having north and south poles with said magnet being incorporated in said holder means on said conveyor below said workpiece with said poles of said magnet oriented so as to establish said field through said casting.

Claim 6

An apparatus for detecting flaws in a workpiece such as a casting or the like comprising means for generating a magnetic field, magnetic field sensing means mounted in spaced relation to said magnetic field generating means and operatively coupled to said field to develop a test signal in response to variations in said field, said generating means and said sensing means being arranged to receive said casting in the space therebetween with said casting disposed in said field, means for striking said casting to cause said casting to vibrate and to thereby cause Said magnetic field to vary in accordance with vibration of said casting and develop in said sensing means a test signal whose frequency and amplitude represent vibration of said casting, and output circuit means responsive to said test signal and operative to detect deviations in said test signal from a corresponding test signal representing vibration of an acceptable casting, and wherein said striking means and said magnetic field sensing means are disposed at a test station and wherein said apparatus further comprises a conveyor movable through said test station and holder means mounted on said conveyor to accommodate a workpiece thereon, said magnetic field generating means comprising a permanent magnet having north and south poles with said magnet being incorporated in said holder means on said conveyor below said workpiece with said poles of said magnet oriented so as to establish said field through said casting.