Abstract Apparatus for magnetic particle inspection and also demagnetization in which a coil around a part or contacts engaged with a part are coupled to the secondary of a stepdown transformer having a primary connected through oppositely poled silicon-controlled rectifiers or the equivalent to an AC source. Control signals are applied to the gates of the siliconcontrolled rectifiers, preferably through a second pair of silicon-controlled rectifiers triggered by a unijunction transistor oscillator the timing of which is controlled to control either magnetizing or demagnetizing current. In magnetizing, an AC field is applied to the part which is always discontinued at the end of a half cycle with a steep wave shape such that the remnant magnetization from one part to another is uniform and the degree of concentration of particles over a defect provides an accurate indication of the character of the defeat. In demagnetization, a circuit including a capacitor is provided for gradually reducing the rate of operation of the oscillator and firing the silicon-controlled rectifiers at progressively later points to gradually reduce the magnetic field in the part and to demagnetize the part.
In demagnetizing apparatus, magnetic field-developing means adapted to be associated with a part to develop a magnetic field therein, a transformer having primary and secondary windings, coupling means for coupling said secondary winding to said magnetic field-developing means, means for coupling said primary winding to a source of alternating current including controlled rectifier means arranged to conduct in both positive and negative half cycles of the alternating current and having control electrode means, and control means for applying control signals to said control electrode means to render said controlled rectifier means conductive at a point in each half cycle of the alternating current to remain conductive until the end of each half cycle, said control means including demagnetization control means for initially applying a control signal at a certain point in a half cycle and for applying control signals at progressively later points in subsequent half cycles to gradually reduce the magnetic field in the part and to demagnetize the part.
Claim 2
Dependent Claim
161 words
In demagnetizing apparatus, magnetic field-developing means adapted to be associated with a part to develop a magnetic field therein, a transformer having primary and secondary windings, coupling means for coupling said secondary winding to said magnetic field-developing means, means for coupling said primary winding to a source of alternating current including controlled rectifier means arranged to conduct in both positive and negative half cycles of the alternating current and having control electrode means, and control means for applying control signals to said control electrode means to render said controlled rectifier means conductive at a point in each half cycle of the alternating current to remain conductive until the end of each half cycle, said control means including demagnetization control means for initially applying a control signal at a certain point in a half cycle and for applying control signals at progressively later points in subsequent half cycles to gradually reduce the magnetic field in the part and to demagnetize the part.
Claim 3
Dependent Claim
73 words
In demagnetizing apparatus as defined in claim 1, said control means including an oscillator arranged to operate during each half cycle, and said demagnetization control means being effective for initiating operation of said oscillator at a certain rate and for progressively reducing the rate of operation of said oscillator to cause application of a control signal at a certain point in one half cycle and at progressively later points in subsequent half cycles.
Claim 4
Dependent Claim
16 words
In demagnetizing apparatus as defined in claim 2, said oscillator being a unijunction transistor relaxation oscillator.
Claim 5
Dependent Claim
38 words
In demagnetizing apparatus as defined in claim 2, said oscillator including a resistor-capacitor timing circuit having a controllable effective resistance and said demagnetization control means including means for gradually changing said controllable effective resistance of said timing circuit.