Apparatus for measuring the thickness of clad material

An apparatus for measuring the thickness of a clad material, said clad material comprising a clad metal and a mother metal, said clad metal having an outer surface and an inner surface, said mother metal having an outer and an inner surface, said clad metal being clad to said mother metal such that the outer surface of said clad metal and the inner surface of said mother metal form a boundary surface, said apparatus comprising:

• a double crystal angle probe contacting the outer surface of said mother metal, said double crystal angle probe comprising:
• a transmitter crystal means for radiating a plurality of ultrasonic beams into said clad material;
• and
• a receiver crystal means for receiving a first echo of an ultrasonic beam from the boundary surface of said mother metal and clad metal, for receiving a second echo of the ultrasonic beam from the inner surface of said clad metal, and for producing first and second echo signals, respectively;
• amplifying means for amplifying said first echo signal with a first amplitude value, and for amplifying said second echo signal with a second amplitude value, said amplifying means being responsive to first and second time sharing signals for alternately amplifying said first and second echo signals with said first amplitude value and said second amplitude value;
• zero point determining means for determining a zero point of time when the transmitter crystal means radiates an ultrasonic beam into said clad material;
• time sharing means for generating said first time sharing signal and said second time sharing signal at predetermined timings;
• detecting means for detecting a time when said amplified first echo signal reaches a first zero-crossing point after a peak of said amplified first echo signal, and for detecting a time when said amplified second echo signal reaches a first zero-crossing point after a peak of said amplified second echo signal;
• period calculating means for calculating a first time period from the zero point of time determined by said zero point determining means to the first zero-crossing point of said amplified first echo signal, and for calculating a second time period from the zero point of time to the first zero-crossing point of said amplified second echo signal;
• and
• thickness calculating means for calculating the thickness of said clad metal and the total thickness of said clad material as a function of said calculated first time period and said calculated second time period.