PULSE AMPLIFIER USED IN ULTRASONIC NONDESTRUCTIVE TESTING

The metal ultrasonic nondestructive testing by the echo-pulse procedure uses short ultrasonic pulses generated by a piezoelectric transducer in contact with the metal, both immersed in water. Short, high amplitude controlled energy electric pulses are furnished to the transducer and converted into short ultrasonic pulses which penetrate the examined material. After propagation through the material, they are reflected by the opposite surface or by the material internal discontinuities and are received by the same transducer which converts them, again, into electric echo-signals. Measuring the ultrasonic pulse round trip duration and supposing the same wave speed through the material is precisely known, the material dimensions and the discontinuities positions will be accurately determined. An algorithm correcting the errors due to the signal phase change on the transducer-material interface ensures an accuracy of 10(-5) in dimension measurement in applications where high precision and sensitivity are asked, without using delay circuits or other procedures specific to such measurements. The nondestructive ultrasonic testing equipment consists in a pulse generator exciting a piezoelectric transducer, an echo-pulse amplifier and a time interval measuring system. In this paper, an echo pulse amplifier is presented, which is characterized by a variable 2-80 dB gain, a distortion factor delta < 0.8 %, a signal-to-noise ratio < 1 % adapted to the impedance of a 17 MHz, spherically focalized ultrasonic transducer used for metallic tubes wall thickness measurement.