Electrical transmission or interconnection systems – Plural supply circuits or sources – Substitute or emergency source
Reexamination Certificate
1999-11-05
2001-11-13
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Plural supply circuits or sources
Substitute or emergency source
C307S087000, C361S267000
Reexamination Certificate
active
06316845
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates, generally, to a portable, battery-operated AC electromagnetic yoke for detecting surface defects in ferrous materials. More particularly, it relates to a circuit that produces a quasi AC square wave voltage so that the inspection is performed by the required method of common practice and is capable of demagnetizing upon completion of inspection.
2. Description of the prior art
There are a number of patents on AC electromagnetic yokes having utility in the field of magnetic particle inspection, but most are reliant upon common 115/230VAC alternating line current and therefore cannot be used in many field applications where 115/230VAC line current is not available or where there may be safety concerns associated with 115/230VAC line current. For example, see U.S. Pat. No. 2,136,375 to DeForest.
There are also patents on battery-powered electromagnetic yokes suitable for use in the field, but they produce DC currents which are not acceptable for most inspection requirements of common practice. Accordingly, these devices lack utility in applications where the inspected part must be in a demagnetized state at the completion of the inspection. U.S. Pat. No. 4,950,989 to Jones discloses a magnetic particle inspector that can use AC or half-wave DC.
Circuits for changing DC to AC, known as inverter circuits, are well known. However, electromagnetic yokes for magnetic particle inspection have inductors that produce large inductances and the power requirements of such yokes are high. Thus, common inverter circuits fail to provide the needed fill, square wave that closely emulates an AC wave.
U.S. Pat. No. 2,447,899 is believed to be the most relevant prior art patent because it discloses an electromagnetic particle inspector unit having a battery-powered circuit for producing an emulated AC voltage. However, the emulated AC voltage is not a true square wave and the device disclosed in that patent cannot generate a magnetic field capable of lifting at least ten pounds. Applicable inspection specifications require that the AC magnetic field generated by the inspection device have a strength sufficient to lift that amount of weight.
What is needed, then, is an electromagnetic particle inspection yoke having a battery-powered circuit that produces a true square wave voltage to provide highly reliable detection of defects in inspected parts. The needed yoke should generate a magnetic field strength capable of lifting at least ten pounds and should be capable of leaving the inspected part in a demagnetized condition.
However, it was not obvious to those of ordinary skill in this art how the needed yoke could be provided, in view of the art considered as a whole at the time the present invention was made.
SUMMARY OF THE INVENTION
The long-standing but heretofore unfulfilled need for an innovation that overcomes the limitations of the prior art is now met by a new, useful, and nonobvious invention. The present invention includes an electromagnetic yoke for magnetic particle inspection. A first battery means supplies a predetermined positive voltage to the electromagnetic yoke and a second battery means supplies a predetermined negative voltage thereto. A switching means switches from the first battery means to the second battery means and back to the first battery means to complete a cycle, continuously performing the switching at a predetermined number of cycles per second. The result is a square waveform that emulates a sinusoidal alternating current waveform so that a ferrous article under inspection is demagnetized at the conclusion of the inspection. The first battery means supplies about sixty positive volts of direct current and the second battery means supplies about sixty negative volts of direct current.
The switching means includes a first clock means that provides a clock pulse having a predetermined frequency for developing the square waveform. The switching means further includes phase splitting means that splits the clock pulse into a first square wave and a second square wave that is shifted in phase one hundred eighty degrees relative to the first square wave. The first and second square waves have a frequency that is one-half the predetermined frequency of the clock pulse. The switching means further includes a pulse shaping means that is triggered on the second square wave and which produces a pulse shaping trigger pulse.
A delay means produces a dwell time pulse that determines the dwell time for the waveform applied to the electromagnetic yoke, the delay means is a second clock means that is triggered by the pulse-shaping trigger pulse. The dwell time pulse is timed so that the dwell time pulse begins before the first and second square waves begin and ends after the first and second square waves have begun.
The switching means further includes a first drive transistor means dedicated to switching the positive DC voltage and a second drive transistor means dedicated to switching the negative DC voltage. The first drive transistor means preferably includes a pair of field effect transistors connected in parallel to one another and the second drive transistor means includes a pair of field effect transistors connected in parallel to one another. The dwell pulse determines the length of time that the first and second transistor means are turned off during each cycle.
A first low voltage logic circuit is associated with the first drive transistor and a second low voltage logic circuit is associated with the second drive transistor. The first low voltage logic circuit includes a first logic gate for turning the first drive transistor on and off and the second low voltage logic circuit includes a second logic gate for turning the second drive transistor on and off.
The first and second low voltage logic circuits respectively include a first and a second inverter means for placing signals applied to said first and second drive transistors, respectively, in a predetermined phase. A pushbutton switch, when closed, applies a positive voltage to the first and second logic gates; this removes drive signals from the drive transistors, thereby biasing the drive transistors into a nonconducting state.
A first battery monitor means monitors the status of the first battery means and a second battery monitoring means monitors the status of the second battery means. The first and second battery monitor means respectively include an optical isolator for isolating high positive and negative voltages produced by the first and second battery means from the first and second low voltage logic circuits.
It is a primary object of this invention to provide a battery-operated electromagnetic yoke for magnetic particle inspection having an emulated AC voltage.
More specific objects are to provide an electromagnetic yoke that generates a magnetic field strength capable of lifting at least ten pounds of a ferrous material and that leaves the inspected article in a demagnetized condition.
These and other important objects, features, and advantages of the invention will become apparent as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.
REFERENCES:
patent: 2110759 (1938-03-01), DeForest
patent: 2136375 (1938-11-01), DeForest
patent: 2158409 (1939-05-01), DeForest et al.
patent: 2447899 (1948-08-01), Coon
patent: 2930972 (1960-03-01), Taylor
patent: 3034021 (1962-05-01), Callihan
patent: 3252074 (1966-05-01), Maine
patent: 3590367 (1971-06-01), Ptomey et al.
patent: 3596143 (1971-07-01), Gruetzmacher et al.
patent: 3855530 (1974-12-01), Fuji et al.
patent: 4058762 (1977-11-01), Holt et al.
patent: 4523250 (1985-06-01), Bacchiere et al.
patent: 4645947 (1987-02-01), Prak
patent: 4950989 (1990-08-01), Jones
patent: 5122743 (1992-06-01), Blakeley et al.
patent: 5311126 (1994-05-01), Mittleman et al.
patent: 5341
Fleming Fritz
Parker Research Corporation
Smith Ronald E.
Smith & Hopen , P.A.
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