Three Ways to Use Ultrasonic Thickness Gauge

An ultrasonic thickness gaugeis one of the most popular industrial non-destructive testing (NDT) tools. It measuresthe thickness of material when only one side is accessible. It functions non-destructively, using ultrasonic waves to detect changes in the material. Before getting in the detail ofdifferent ways to use an ultrasonic thickness gauge, it is necessary to understand how these gauges work.

A dual-element transducer consists of two crystals. In this gauge, the ultrasonic waves sent from one crystal create a 'V' pattern by hitting the material's back wall and reaching the other crystal. The gauge measures the time taken for the ultrasonic pulse to travel to and forth. Taking variables like the speed of the pulse, material, and any potential acoustic barriers, it calculates the wall's thickness. A single element transducer uses only one crystal to send and receive the pulse.

Here are the three ways to use an ultrasonic thickness gauge:

        i  For coated materials: When a material is coated, it is necessary to ignore the time the pulse neededto pass through the coating. In this case, it is the difference in time between the first echo and the second echo that is measured. The first echo occurs from the pules hitting the back wall of the material for the first time. The second echo occurs when the pulse is reflected once again to the back wall. The two successive back wall echoes do not include the time the pulse takes to travel through the material.

      ii.  For thin uncoated materials: In thin and uncoated materials, measurement of the thickness is hard. This is because the gap between the outgoing pulse and the returning echo is too short to measure. Hence, professionals use a delay line in this case. They measure the time taken for the pulse to travel from the interface to the echo.

    iii. To measure very thin materials accurately: For materials as thin as 0.15mm, the time between the two echoes is measured. The gauge still records the interface time as it would have to remove the delay line for the results.

Each of these three methods is effective for a specific purpose. It is imperative to pick the right one based on the material you need to measure.

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