mi 3,848,182  Nov. 12, 1974
[ 54 ] APPARATUS FOR LIMITING
PHASE-ANGLE RESPONSE RANGE,
PARTICULARLY IN EDDY CURRENT
 Inventors: James Gerner, Elmhurst; Peter J.
Suhr, Garden City, both of N.Y.
 Assignee: Magnetic Analysis Corporation, Mt. Vernon, N.Y.
 Filed: . Aug. 15, 1973
 Appl. No.: 388,568
 U.S. CI 324/40
 Int. CI GOlr 33/12
 Field of Search 324/37, 40
 References Cited
UNITED STATES PATENTS 3,405,354 10/1968 Callan et al 324/40
Primary Examiner—Robert J. Corcoran
Attorney, Agent, or Firm—Pennie & Edmonds
In eddy current testing apparatus utilizing quadrature signal detection, the quadrature signal components are multiplied by respective sine and cosine functions of an adjustable sine-cosine multiplying means to yield respective signals of substantially equal amplitude at a phase angle of the quadrature signal components depending on the setting of the multiplying means. Combining means yields minimum or substantially zero output when the signals are equal in amplitude, and a progressively increasing output as they become unequal. The resultant output is applied to an adjustable threshold circuit to produce a gate signal when the output lies within the angular sector desired. The gate signal may be used to control the passage of the quadrature signal components to an oscilloscope display, and the passage of vector signal jimplitudeto a threshold control circuit for classification such as marking, recording, etc. Thus the phase angle response may be limited to a desired range which is readily adjustable both in angular position and width. The arrangement may be useful in environments other than eddy current testing.
6 Claims, 4 Drawing Figures