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Ultrasonic thickness gauge measures why couplant is used
Sep 26, 2018

Ultrasonic thickness gauge measures why couplant is used

Let's talk about the small series below. Why should the ultrasonic thickness gauge measure the coupling agent?

Ultrasonic waves are attenuated sharply when exposed to air. In order to allow the air between the ultrasonic probe and the workpiece to be expelled, ultrasonic couplant is removed. Usually, the surface of the workpiece that is smooth at the factory is measured by general engine oil or other non-corrosive liquid. The rougher surface can be made of relatively viscous butter. After the measurement, the probe surface and the standard block surface coupling agent must be erased.

The method for detecting the thickness by the ultrasonic thickness gauge includes a resonance method, an interference method, a pulse echo method, and the like. The non-destructive testing resource network now mainly uses the pulse echo method to detect the working principle of thickness.

The ultrasonic probe is in contact with the surface of the object to be measured. The main controller controls the transmitting circuit so that the ultrasonic wave emitted by the probe reaches the bottom surface of the object to be measured, and the pulse signal is received by the probe and amplified by the amplifier to be added to the vertical deflection plate of the oscilloscope. The marker generator outputs a time stamp pulse signal and simultaneously applies to the vertical deflection plate. The scanning voltage is applied to the horizontal deflection plate. Therefore, the time interval t between transmitting and receiving ultrasonic waves can be directly read out on the oscilloscope. The thickness h of the measured object is: h = ct/2, where c is the propagation speed of the ultrasonic wave.

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