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Pulse Echo


  •          Flaws are detected by measuring the amplitude of signals reflected and the time required for these signals to travel between specific surfaces and the discontinuity.
  • The time base, triggered simultaneously with each transmission pulse, causes a spot to sweep across the screen of the CRT or LCD. The spot sweeps from left to right across the face of the scope 50 to 5,000 times per second or higher is required for high-speed automated scanning.
  •  Due to the speed of the cycle of transmitting and receiving, the picture on the oscilloscope appears to be stationary.
  • A few microseconds after the sweep is initiated, the rate generator electrically excites the pulse, and the pulse in turn emits an electrical pulse.
  •  The transducer converts this pulse into a short train of ultrasonic sound waves. If the interfaces of the transducer and the specimen are properly oriented, the ultrasound is reflected back to the transducer when it reaches the internal flaw and the opposite surface of the specimen.
  • The time interval between the transmission of the initial impulse and the reception of the signals from within the specimen are measured by the timing circuits.
  •  The reflected pulse received by the transducer is amplified, transmitted to, and displayed on the instrument screen. The pulse is displayed in the same relationship to the front and back pulses as the flaw is in relation to the front and back surfaces of the specimen.
  • Pulse-echo instruments may also be used to detect flaws not directly underneath the probe by use of the angle beam testing method. Angle beam testing differs from straight beam testing only in the manner that the ultrasonic waves pass through the material being tested.

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