Ultrasonic thickness gauge

An ultrasonic thickness gauge is a measuring instrument for the non-destructive investigation of a material's thickness using ultrasonic waves.

The usage of an ultrasonic thickness gauge for non-destructive testing to check material properties such as thickness measurement, is now regularly utilized in all areas of industrial measurements. The ability to gauge thickness measurement without requiring access to both sides of the test piece, offers this technology a multitude of possible applications. Paint thickness gauge, ultrasonic coating thickness gauge, digital thickness gauges and many more options are available to test plastics, glass, ceramics, metal and other materials.

A rugged ultrasonic thickness gauge determines sample thickness by measuring the amount of time it takes for sound to traverse from the transducer through the material to the back end of a part and back. The ultrasonic thickness gauge then calculates the data based on the speed of the sound through the tested sample.

The very first ultrasonic thickness gauge was made in 1967 by Werner Sobek; a Polish engineer from Katowice. This first ultrasonic thickness gauge measured the velocity of the waves it emitted in particular test samples, it then calculated the thickness in micrometers from this speed measurement by an applied mathematical equation.

There are two types of transducers that can be used as an ultrasonic thickness gauge. These sensors are piezoelectric and EMAT sensors. Both transducer types emit sound waves into the material when excited. Typically these transducers use a predetermined frequency, however certain thickness gauges allow for frequency tuning in order to inspect a wider range of material. A standard frequency used by an ultrasonic thickness gauge is 5 MHz.

Some ultrasonic coating thickness gauges require that a couplant in gel, paste or liquid format be used to eliminate gaps between the transducer and the test piece. One common couplant is propylene glycol, but there are many other options which can be substituted.

Today there are many high tech models on the market. Modern digital thickness gauge has the capability of saving data and outputting to a variety of other data logging devices. A user friendly interface and saved data and settings allows for the utmost of ease for operators. This allows for even relatively novice users to obtain cost effective and accurate measurements.

Advantages and disadvantages

Ultrasonic thickness gauge advantages:

Non-destructive technique
Does not require access to both sides of the sample
Can be engineered to cope with coatings, linings, etc.
Good accuracy (0.1 mm and less) can be achieved using standard timing techniques
Can be easily deployed, does not require laboratory conditions
EMAT Transducers can be used without liquid couplant

Ultrasonic thickness gauge disadvantages:

Usually requires calibration for each material
Requires good contact with the material

Digital thickness gauge typical usage

UTM is frequently used to monitor steel thickness in various places of ships and offshore constructions. Surveyors equipped with portable UTM probes reach steel plating in sides, tanks, decks and the superstructure. They can read its thickness by simply touching the steel with the measurement head. Contact is usually assured by first removing visible corrosion scale and then applying petroleum jelly before pressing the probe against metal. It is also used for monitoring pipelines.

References

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