Flaw detection device having a movable pick-up unit for developing a frequency modulated signal that is transmitted to a stationary indicating unit

Claim 1

A SEAM DEPTH INDICATOR COMPRISING A MOVABLE STRUCTURE INCLUDING AN OSCILLATORY SYSTEM HAVING A RESONANT CIRCUIT ESTABLISHING THE FREQUENCY OF OSCILLATION THEREOF, MEANS INCLUDED IN SAID SYSTEM FOR ESTABLISHING LONG-TERM STEADY-STATE OSCILLATION AMPLITUDE STABILIZATION THEREOF WHILE PERMITTING SHORT-TERM OSCILLATION AMPLITUDE INSTABILITY THEREOF, AND EXPLORING INDUCTOR INCLUDED IN SAID RESONANT CIRCUIT FOR PRODUCING AN OSCILLATORY MAGNETIC FIELD EXTERNAL TO SAID SYSTEM AND MOVABLE WITH SAID STRUCTURE OVER THE SURFACE OF A METALLIC BODY TO DEVELOP BY REASON OF EDDYCURRENT LOSSES PRODUCED IN SAID BODY BY SAID FIELD AN OSCILLATORY-SYSTEM TRANSIENT OSCILLATION AMPLITUDE VARIATION INDICATIVE OF THE PRESENCE OF A SEAM-LIKE FLAW IN THE VICINITY OF THE SURFACE OF SAID BODY, MEANS CARRIED BY SAID STRUCTURE AND CONTROLLED BY SAID OSCILLATORY SYSTEM FOR GENERATING AND TRANSMITTING AN ELECTROMAGNETIC CARRIER WAVE FREQUENCY MODULATED ACCORDING TO EACH SAID TRANSIENT OSCILLATION AMPLITUDE VARIATION, AND STATIONARY MEANS FOR RECEIVING SAID MODULATED CARRIER WAVE AND FOR DERIVING AND UTILIZING THE MODULATION COMPONENT THEREOF TO INDICATE THE PRESENCE OF SAID SEAM-LIKE FLAWS IN SAID BODY.