How to Use Ultrasonic Thickness Gauge?

Ultrasonic non-destructive testing is a technique that is very close to the ultrasound control used in medicine. Mostly we speak of ultrasound technique. It consists of sending an ultrasonic wave using a translator in a material that can be metallic, composite, plastic, or ceramic and in collecting the presence or absence of reflection signals on internal discontinuities of the material (cracks, porosities, inclusions, etc …). It is a volume technique that is the opposite of penetrant testing, magnetoscope and eddy currents, capable of locating and dimensioning internal defects. It can be used in manual or automated mode, most often using a single access surface including for large parts and distances of several meters. Unlike X-rays, it does not present any risk regarding occupational safety and health.

There are times when we need to have a little information about a piece or some type of material, for example, the thickness of it, without the need to make any cut of that material, for which Ultrasound created the Thickness Gauge.

These devices are not new, since they were created in the 1960s, as a derivation of sonar, and from those days until the recent era, they have evolved significantly.

This is a method that requires a relatively high technical level of operators but is promised a very bright future with the advent of imaging techniques TOFD and Multielement Phased Array.

The principles of ultrasonic thickness measurement

• Use of separate transmit/receive translators, allowing a “pseudo-focusing” for better detection of the corrosion while being independent of the state of the surface.
• Precision on the order of 0.1 mm in steel (accuracy dependent on material + material + calibration)
• In some cases (measurements undercoatings for example) it is necessary to visualize the ultrasonic signal.

How an Ultrasonic Thickness Gauge works

To understand the operation of this device, it is necessary to know that ultrasound is the energy of sound at frequencies that exceed the limit of the human ear.

And is that most ultrasound tests are performed in the frequency range between 500 KHz and 20 MHz, and some specialized instruments can operate at 50 KHz or less and 100 MHz or more.

The operation of the Ultrasonic Thickness Gauge is based on determining with high precision what is called flight time, which is the time it takes for a pulse of sound generated by a small probe called an ultrasonic transducer to pass through a piece and return to the device.

At the same time, that transducer contains a piezoelectric element that is stimulated by a short electrical impulse to generate a burst of ultrasonic waves.

It is there that the waves are coupled into the material and pass through it until they find a back wall or other limit and then the reflections go back to the transducer, which converts the acoustic energy into electrical energy.

And with this process, you can measure any common engineering material by using ultrasound and it is possible to configure ultrasonic thickness gauges for metals, plastics, composites, fiberglass, ceramics and glass.