Frequency controlled hartley oscillator circuit for non-destructive eddy current testing of an electrically conductive material

Claim 1

An apparatus for non-destructively testing the characteristics of an electrically conductive material comprising: an oscillator circuit which includes an inductive winding connected therewith, said material to be tested being inductively coupled with said oscillator circuit winding; means for generating and supplying an alternating current voltage to said oscillator circuit winding so as to generate eddy-currents in said material; and means for indicating the output of said oscillator circuit in response to eddy-currents in said material with respect to the frequency of said alternating current voltage supplied to said oscillator circuit winding, wherein said inductive winding is coupled at one terminal thereof to a first electrode of an active element included in said oscillator circuit and aT another terminal thereof to another electrode of said active element and wherein the first electrode of said active element serves as the cathode and is connected to an intermediate point of said winding and said means for indicating the output of said oscillator circuit according to said frequency of said alternating current is connected to the said another electrode of said active element which serves as the grid of said active element, the oscillator output being the variations in the grid voltage which voltage corresponds to the voltage developed across said winding and further including means, connected to said alternating current voltage generating and supplying means, for controlling the frequency of the current supplied thereby to said oscillator circuit winding, the alternating current voltage generating means providing a signal, the frequency of which is dependent upon the output of said control means, wherein said frequency control means comprises a generator for producing saw-toothed signals which increase along a linear ramp in successive steps and connected to said alternating-current voltage generating means which serves to vary the frequency in a series of the uniformly spaced stages having a duration corresponding substantially to the time required to ensure that a material under inspection which is driven in translational motion by suitable transfer means should traverse one pass within said winding.

Claim 2

An apparatus for non-destructively testing the characteristics of an electrically conductive material comprising: an oscillator circuit which includes an inductive winding connected therewith, said material to be tested being inductively coupled with said oscillator circuit winding; means for generating and supplying an alternating current voltage to said oscillator circuit winding so as to generate eddy-currents in said material; and means for indicating the output of said oscillator circuit in response to eddy-currents in said material with respect to the frequency of said alternating current voltage supplied to said oscillator circuit winding, wherein said inductive winding is coupled at one terminal thereof to a first electrode of an active element included in said oscillator circuit and aT another terminal thereof to another electrode of said active element and wherein the first electrode of said active element serves as the cathode and is connected to an intermediate point of said winding and said means for indicating the output of said oscillator circuit according to said frequency of said alternating current is connected to the said another electrode of said active element which serves as the grid of said active element, the oscillator output being the variations in the grid voltage which voltage corresponds to the voltage developed across said winding and further including means, connected to said alternating current voltage generating and supplying means, for controlling the frequency of the current supplied thereby to said oscillator circuit winding, the alternating current voltage generating means providing a signal, the frequency of which is dependent upon the output of said control means, wherein said frequency control means comprises a generator for producing saw-toothed signals which increase along a linear ramp in successive steps and connected to said alternating-current voltage generating means which serves to vary the frequency in a series of the uniformly spaced stages having a duration corresponding substantially to the time required to ensure that a material under inspection which is driven in translational motion by suitable transfer means should traverse one pass within said winding.

Claim 4

An apparatus for non-destructively testing the characteristics of an electrically conductive material comprising: an oscillator circuit which includes an inductive winding connected therewith, said material to be tested being inductively coupled with said oscillator circuit winding; means for generating and supplying an alternating current voltage to said oscillator circuit winding so as to generate eddy-currents in said material; and means for indicating the output of said oscillator circuit in response to eddy-currents in said material with respect to the frequency of said alternating current voltage supplied to said oscillator circuit winding, wherein said inductive winding is coupled at one terminal thereof to a first electrode of an active element included in said oscillator circuit and at another terminal thereof to another electrode of said active element and wherein the first electrode of said active element serves as the cathode and is connected to an intermediate point of said winding and said means for indicating the output of said oscillator circuit according to said frequency of said alternating current is connected to the said another electrode of said active element which serves as the grid of said active element, the oscillator output being the variations in the grid voltage which voltage corresponds to the voltage developed across said winding and further including means, connected to said alternating current voltage generating and supplying means, for controlling the frequency of the current supplied thereby to said oscillator circuit winding, the alternating current voltage generating means providing a signal, the frequency of which is dependent upon the output of said control means, and wherein said frequency control means comprises a direct-curreNt voltage generator having a plurality of outputs which deliver voltages having different values and a selector switch for successively applying said direct-current voltages to the alternating-current voltage generating means in order that the frequency thereof will assume a number of different values wherein said apparatus comprises a program device which is adapted to initiate a sequence of several passes within the winding in the case of each material to be inspected and at the same time to cause a change of position of said selector switch for each pass, a threshold circuit for receiving the grid voltage of the active element and a storage device connected to the output of said threshold circuit for recording the triggering of said circuit at each pass and said storage device being intended to control an apparatus for the removal of defective parts according to the information which is recorded.

Claim 5

An apparatus for non-destructively testing the characteristics of an electrically conductive material comprising: an oscillator circuit which includes an inductive winding connected therewith, said material to be tested being inductively coupled with said oscillator circuit winding; means for generating and supplying an alternating current voltage to said oscillator circuit winding so as to generate eddy-currents in said material; and means for indicating the output of said oscillator circuit in response to eddy-currents in said material with respect to the frequency of said alternating current voltage supplied to said oscillator circuit winding, wherein said inductive winding is coupled at one terminal thereof to a first electrode of an active element included in said oscillator circuit and at another terminal thereof to another electrode of said active element and wherein the first electrode of said active element serves as the cathode and is connected to an intermediate point of said winding and said means for indicating the output of said oscillator circuit according to said frequency of said alternating current is connected to the said another electrode of said active element which serves as the grid of said active element, the oscillator output being the variations in the grid voltage which voltage corresponds to the voltage developed across said winding and further including means, connected to said alternating current voltage generating and supplying means, for controlling the frequency of the current supplied thereby to said oscillator circuit winding, the alternating current voltage generating means providing a signal, the frequency of which is dependent upon the output of said control means, and wherein said frequency control means comprises a direct-curreNt voltage generator having a plurality of outputs which deliver voltages having different values and a selector switch for successively applying said direct-current voltages to the alternating-current voltage generating means in order that the frequency thereof will assume a number of different values wherein said apparatus comprises a program device which is adapted to initiate a sequence of several passes within the winding in the case of each material to be inspected and at the same time to cause a change of position of said selector switch for each pass, a threshold circuit for receiving the grid voltage of the active element and a storage device connected to the output of said threshold circuit for recording the triggering of said circuit at each pass and said storage device being intended to control an apparatus for the removal of defective parts according to the information which is recorded.

Claim 6

An apparatus for non-destructively testing the characteristics of an electrically conductive material comprising: an oscillator circuit which includes an inductive winding connected therewith, said material to be tested being inductively coupled with said oscillator circuit winding; means for generating and supplying an alternating current voltage to said oscillator circuit winding so as to generate eddy-currents in said material ; and means for indicating the output of said oscillator circuit in response to eddy-currents in said material with respect to the frequency of said alternating current voltage supplied to said oscillator circuit winding, wherein said inductive winding is coupled at one terminal thereof to a first electrode of an active element included in said oscillator circuit and at another terminal thereof to another electrode of said active element and wherein the first electrode of said active element serves as the cathode and is connected to an intermediate point of said winding and said means for indicating the output of said oscillator circuit according to said frequency of said alternating current is connected to the grid another electrode of said active element which serves as the grid of said active element, the oscillator output being the variations in the grid voltage which voltage corresponds to the voltage developed across said winding and further including means, connected to said alternating current voltage generating and supplying means, for controlling the frequency of the current supplied thereby to said oscillator circuit winding, the alternating current voltage generating means providing a signal, the frequency of which is dependent upon the output of said control means, wherein said frequency control means comprises a saw-tooth signal generator connectable to said alternating-current voltage generating means for causing said frequency to vary cyclically and continuously, a generator for producing saw-tooth signals which increase in successive steps, connectable to said alternating current voltage generating means for varying said frequency in a series of uniformly spaced stages having a duration corresponding substantially to the time required to ensure that a material under inspection will traverse one pass through said winding, and including means for displacing said material within said winding, and a direct-current voltage generator having a plurality of outputs which deliver voltages having different values and a selector switch connectable to said alternating-current voltage generator means for successively applying said direct-current voltages to said alternating current voltage generating means in order that the frequency thereof will assume a number of different values in succession and further including a selector switch for selective connecting one of said continuously and cyclically varying saw-tooth signal generator, said successive step increasing saw-tooth signal generator and said direct-current voltage generator to said alternating current voltage generating means.

Claim 7

An apparatus for non-destructively testing the characteristics of an electrically conductive material comprising: an oscillator circuit which includes an inductive winding connected therewith, said material to be tested being inductively coupled with said oscillator circuit winding; means for generating and supplying an alternating current voltage to said oscillator circuit winding so as to generate eddy-currents in said material ; and means for indicating the output of said oscillator circuit in response to eddy-currents in said material with respect to the frequency of said alternating current voltage supplied to said oscillator circuit winding, wherein said inductive winding is coupled at one terminal thereof to a first electrode of an active element included in said oscillator circuit and at another terminal thereof to another electrode of said active element and wherein the first electrode of said active element serves as the cathode and is connected to an intermediate point of said winding and said means for indicating the output of said oscillator circuit according to said frequency of said alternating current is connected to the grid another electrode of said active element which serves as the grid of said active element, the oscillator output being the variations in the grid voltage which voltage corresponds to the voltage developed across said winding and further including means, connected to said alternating current voltage generating and supplying means, for controlling the frequency of the current supplied thereby to said oscillator circuit winding, the alternating current voltage generating means providing a signal, the frequency of which is dependent upon the output of said control means, wherein said frequency control means comprises a saw-tooth signal generator connectable to said alternating-current voltage generating means for causing said frequency to vary cyclically and continuously, a generator for producing saw-tooth signals which increase in successive steps, connectable to said alternating current voltage generating means for varying said frequency in a series of uniformly spaced stages having a duration corresponding substantially to the time required to ensure that a material under inspection will traverse one pass through said winding, and including means for displacing said material within said winding, and a direct-current voltage generator having a plurality of outputs which deliver voltages having different values and a selector switch connectable to said alternating-current voltage generator means for successively applying said direct-current voltages to said alternating current voltage generating means in order that the frequency thereof will assume a number of different values in succession and further including a selector switch for selective connecting one of said continuously and cyclically varying saw-tooth signal generator, said successive step increasing saw-tooth signal generator and said direct-current voltage generator to said alternating current voltage generating means.