Pulse eddy current testing apparatus with ramp phase shifter

Claim 2

In a pulse eddy current testing apparatus including a pulse generator, test coil means supplied with pulses from said generator for inducing eddy currents in an object under test and producing output signals varying with defects or flaws in the object, phase-sensitive detector means supplied with output signals from said test coil means, and means for utilizing signals from the phase-sensitive detector means to produce indications of said defects or flaws; means for producing time adjustable gate pulses for said phase-sensitive detector means which comprises a. a ramp generator responsive to pulses from said pulse generator for producing respective ramps following respective pulses, b. an adjustable level control circuit supplied with said ramps for changing the DC level thereof, c. an electronic switching circuit supplied with ramps from said adjustable level control circuit for switching the output state thereof at a predetermined instantaneous value of successive ramps supplied thereto, d. and means responsive to said switching for producing respective gate pulses, e. said gate means being supplied to said phase-sensitive detector means.

Claim 3

Apparatus according to claim 1 in which said adjustable level control circuit includes a clamping circuit having an adjustable clamping level, and AC coupling means for supplying ramps from said ramp generator to said clamping circuit to clamp the initial portions of the ramps to said adjustable clamping level.

Claim 4

Apparatus according to claim 1 in which said electronic switching circuit is a switching amplifier biased to switch the output state thereof at said instantaneous value of the ramps supplied thereto and produce a series of output pulses, and said means responsive to the switching is responsive to the leading edges of the series of output pulses to produce a corresponding series of gate pulses.

Claim 5

Apparatus according to claim 3 including limiting means for limiting the output of said switching amplifier to a predetermined magnitude.

Claim 6

In pulse eddy current testing apparatus including a pulse generator, test coil means supplied with pulses from said generator for inducing eddy currents in an object under test and producing output signals varying with defects or flaws in the object, a pair of phase-sensitive detectors supplied with output signals from said test coil means, and means for utilizing signals from the phase-sensitive detectors to produce indications of said defects or flaws; means for producing time adjustable pairs of gate pulses for said phase-sensitive detectors which comprises a. a ramp generator responsive to pulses from said pulse generator for producing respective ramps following respective pulses, b. an adjustable level control circuit sUpplied with said ramps for changing the DC level thereof, c. a pair of electronic switching circuits supplied with ramps from said adjustable level control circuit for switching the output stage thereof at different instantaneous values of the ramps supplied thereto, d. and respective means responsive to the switching of said pair of switching circuits for producing pairs of gate pulses spaced in time between the pulses from said pulse generator, e. said pairs of gate pulses being supplied to said pair of phase-sensitive detectors respectively.

Claim 7

In pulse eddy current testing apparatus including a pulse generator, test coil means supplied with pulses from said generator for inducing eddy currents in an object under test and producing output signals varying with defects or flaws in the object, a pair of phase-sensitive detectors supplied with output signals from said test coil means, and means for utilizing signals from the phase-sensitive detectors to produce indications of said defects or flaws; means for producing time adjustable pairs of gate pulses for said phase-sensitive detectors which comprises a. a ramp generator responsive to pulses from said pulse generator for producing respective ramps following respective pulses, b. an adjustable level control circuit sUpplied with said ramps for changing the DC level thereof, c. a pair of electronic switching circuits supplied with ramps from said adjustable level control circuit for switching the output stage thereof at different instantaneous values of the ramps supplied thereto, d. and respective means responsive to the switching of said pair of switching circuits for producing pairs of gate pulses spaced in time between the pulses from said pulse generator, e. said pairs of gate pulses being supplied to said pair of phase-sensitive detectors respectively.

Claim 8

Apparatus according to claim 5 in which said adjustable level control circuit includes a clamping circuit having an adjustable clamping level, and AC coupling means for supplying ramps from said ramp generator to said clamping circuit to clamp the initial portions of the ramps to said adjustable clamping level.

Claim 9

In pulse eddy current testing apparatus including a pulse generator, test coil means supplied with pulses from said generator for inducing eddy currents in an object under test and producing output signals varying with defects or flaws in the object, a pair of phase-sensitive detectors supplied with output signals from said test coil means, and means for utilizing signals from the phase-sensitive detectors to produce indications of said defects or flaws; means for producing time adjustable pairs of gate pulses for said phase-sensitive detectors which comprises a. a ramp generator responsive to pulses from said pulse generator for producing respective ramps following respective pulses, b. a clamping circuit having an adjustable clamping level, c. AC coupling means for supplying said ramps to said clamping circuit to clamp the initial portions of the ramps to said adjustable clamping level, d. a pair of switching amplifiers supplied with ramps from said clamping circuit, e. means for biasing said switching amplifiers to switch the output states thereof at different instantaneous values of the ramps supplied thereto and produce pairs of output pulses initiated at different instants during respective ramps, f. and respective means responsive to the leading edges of the output pulses from said switching amplifiers for producing pairs of gate pulses spaced in time between the pulses from said pulse generator, g. said pairs of gate pulses being supplied to said pair of phase-sensitive detectors respectively.

Claim 10

In pulse eddy current testing apparatus including a pulse generator, test coil means supplied with pulses from said generator for inducing eddy currents in an object under test and producing output signals varying with defects or flaws in the object, a pair of phase-sensitive detectors supplied with output signals from said test coil means, and means for utilizing signals from the phase-sensitive detectors to produce indications of said defects or flaws; means for producing time adjustable pairs of gate pulses for said phase-sensitive detectors which comprises a. a ramp generator responsive to pulses from said pulse generator for producing respective ramps following respective pulses, b. a clamping circuit having an adjustable clamping level, c. AC coupling means for supplying said ramps to said clamping circuit to clamp the initial portions of the ramps to said adjustable clamping level, d. a pair of switching amplifiers supplied with ramps from said clamping circuit, e. means for biasing said switching amplifiers to switch the output states thereof at different instantaneous values of the ramps supplied thereto and produce pairs of output pulses initiated at different instants during respective ramps, f. and respective means responsive to the leading edges of the output pulses from said switching amplifiers for producing pairs of gate pulses spaced in time between the pulses from said pulse generator, g. said pairs of gate pulses being supplied to said pair of phase-sensitive detectors respectively.

Claim 11

Apparatus according to claim 7 in which the means for biasing at least one of said switching amplifiers is adjustable.

Claim 12

Apparatus according to claim 7 including limiting means in the output circuit of each of said switching amplifiers for limiting the outputs thereof to predetermined magnitudes.