Ultrasonic Wall Thickness Measurement

Ultrasonic thickness measurement is a sophisticated technique that leverages ultrasound's ability to pass through various materials and measure the time it takes to do so. This technique is based on the premise that the time it takes for ultrasound to travel through a material is directly proportional to its thickness, allowing for an accurate estimation of the latter.

1. Measurement Principle and Speed of Sound The key to accurate thickness measurement via ultrasound lies in knowing the sound speed within the material. Properly setting the sound speed in the device is crucial and can be automatically performed using an integrated calibration function that utilizes a pattern of known thickness. This ensures precise measurement by adjusting to the material's specific characteristics. Typical sound speeds vary by material, which can significantly affect accuracy if not properly adjusted.

2. Suitability of Materials Not all materials are suitable for ultrasonic thickness measurement. Homogeneous materials such as metals, plastics, glass, and ceramics are ideal for this type of testing. However, composite materials, some types of plastics, and non-homogeneous materials like wood and concrete present challenges due to their structure, which can scatter or absorb sound inefficiently.

3. Measurement Range and Accuracy The range and accuracy of ultrasonic thickness measurement greatly depend on the nature of the material and the probe used. For example, steel can be measured with high precision due to its low variability in sound speed across the sample, whereas cast iron may exhibit greater variations due to its granular structure.

4. Coupling Agent For ultrasound to be effectively transmitted from the transducer to the material, the use of a coupling agent is essential. This medium, typically a viscous liquid, eliminates air between the transducer and the material, facilitating effective sound transmission.

5. Influence of Temperature The material's temperature can significantly affect the sound speed, and therefore, the measurement results. High temperatures not only affect the sound speed but can also damage the transducer or make the use of water-based coupling agents unsuitable. For this reason, it is crucial to calibrate and measure at a constant and known temperature.

Device Pulse-Echo Mode: This mode measures the total thickness between the probe and the material's rear wall. The measurement captures the interval from the first pulse to the first back wall echo. Ideal for detecting small defects, Pulse-Echo mode requires that the probe be calibrated with the zero plate before each measurement. It is important to note that this mode is suitable only for uncoated materials.

Echo-Echo Mode: In this mode, the time between two reflected echoes from the material's back wall and surface is measured. This method is effective for both coated and uncoated materials, as it automatically ignores any surface layer. However, it requires a much stronger and clearer return echo to perform effective measurement.

Echo-Echo-Verify Mode: Functions similarly to Echo-Echo mode but adds an additional verification using a third echo. This mode provides greater security in measurement and is especially valuable in critical applications such as shipbuilding, where precision is paramount.

Interface Echo Mode: This mode specializes in precision thickness measurement of wall using the delay tip of the precision probe and the first back wall echo. It is important to mention that Interface Echo mode is suitable exclusively for uncoated materials, as it measures directly from the probe's interface to the material.

Before commencing with wall thickness measurement, it is crucial to perform proper calibration of the meter. This preparation ensures that measurement results are accurate and reliable.

Calibration Methods:

• Direct Introduction: If you already know the sound speed in the material to be measured, simply enter it through the meter's control panel. This allows you to proceed directly with the measurement.
• Sample-Based Calibration: If the exact sound speed of the material is unknown, you can opt for a one- or two-point calibration. This method involves measuring the thickness of a sample whose thickness is previously known with a caliper. Subsequently, conduct a measurement with the thickness meter and adjust the device by entering the actual thickness value. The device will automatically calculate the sound speed and display it on the screen, facilitating future settings.

Importance of Calibration: All models from TI-25MX upwards include the calibration function, highlighting the importance of choosing a device that offers this capability to maximize accuracy and ease of use. We recommend selecting a meter with integrated calibration functionality to achieve the best results in your measurements.