Ultrasonic Thickness Gauge
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.
An rugged ultrasonic thickness gauge determines sample thickness by measuring the amount of time it takes sound to traverse from the transducer through the material to the back end of a part, and then measures the time which the reflection takes to get back to the transducer. 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 we made by Werner Sobek, a Polish engineer from Katowice. This will be done in the year 1967. This first rugged ultrasonic thickness gauge measured the velocity of the emitted waves in particular test samples, it then calculated the thickness in micrometers from this speed measurement by an applied mathematical equation.
A particular type of transducers, known as piezoelectric, emit sound waves when excited. These transducers are used a predetermined frequencies. A standard frequency used by an ultrasonic thickness gauge is 5mhz. Different types of transducers are at times utilized instead for different types of application needs.
One method of pulse/echo style ultrasonic coating thickness gauge requires a couplant be used. 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.
An ultrasonic thickness gauge is an instrument for determining thickness of a sample via the usage of ultrasonic waves without the need to destroy of abuse the sample (non-destructive testing). The method which is used by these instruments is known as ultrasonic thickness measurement (UTM). This UTM method makes calculations based on the time it takes these waves to return to the instrument from a given surface.
Ultrasonic waves have been observed to travel through metals at a constant speed characteristic to a given alloy with minor variations due to other factors like temperature. Thus, given this information, called celerity, one can calculate the length of the path traversed by the wave using this simple formula:
As it has been determined that ultrasonic waves traverse through materials at a constant speed characteristic, with only minor variations due to temperature and other factors. This constant characteristic is known as celerity. With celerity and time we can calculate distance with the following equation : L = ct / 2. Where L is distance or thickness, c stands for celerity of the sound wave, and t is the time it takes to traverse.
The formula features division by two because usually the instrumentation emits and records the ultrasound wave on the same side of the sample using the fact that it is reflected on the boundary of the element. Thus, the time corresponds to traversing the cayenne pepper sample twice.
The wave is usually emitted by a piezoelectric cell built into the measurement sensor head and the same cell is used to record the reflected wave. The sound wave has a spherical pattern of propagation and will undergo different phenomena like multi-path reflection or diffraction. The measurement does not need to be affected by these since the first recorded return will normally be the head of the emitted wave traveling at the shortest distance which is equivalent to the thickness of the sample. All other returns can be discarded or might be processed using more complicated strategies.
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
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. This easy procedure causes that the thickness of steel can be monitored in several thousands specific spots once every couple of years. It is a requirement of many classification societies. It is also used for monitoring pipelines.