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Analysis Of Causes Of Errors In Ultrasonic Thickness Gauge
Nov 14, 2018

Analysis of Causes of Errors in Ultrasonic Thickness Gauge


Let's take a look at the following small series. Analysis of the causes of errors in ultrasonic thickness gauges.


1. Laminated material and composite (non-homogeneous) material. It is impossible to measure uncoupled laminated materials because ultrasonic waves cannot penetrate uncoupled spaces and cannot propagate at a constant rate in composite (non-homogeneous) materials. For equipment made of multi-layer material (like urea high-pressure equipment), special care should be taken when measuring thickness. The thickness gauge indicates only the thickness of the material that is in contact with the probe.


2. The sound speed selection is wrong. Before measuring the part, preset its sound speed according to the material type or reverse the sound speed according to the standard block. When the instrument is calibrated with one material (usually the test block is steel) and another material is measured, an erroneous result will result.


3. The effect of temperature. In general, the speed of sound in solid materials decreases with increasing temperature. Test data shows that for every 100 °C increase in hot material, the speed of sound drops by one percent. This is often the case with high temperature in-service equipment.


4. The influence of the coupling agent. The coupling agent is used to exclude the air between the probe and the object to be measured, so that the ultrasonic wave can effectively penetrate the component for inspection purposes. If the type is selected or the method of use is improper, it will cause an error or the coupling mark will flash and cannot be measured. In actual use, the instrument indicates the value of the couplant layer thickness due to the excessive use of the couplant, causing the probe to leave the part.