Ultrasonic thickness gauges measure time to measure the thickness of the material being tested. It relies on the principal that sound travels through a material at a constant velocity or speed.
If you can accurately measure the time it takes to travel through a material, and you know its velocity then you can calculate its thickness.
There are tables listing the velocity of most common metals and materials, but these velocities are only “typical” values. For example Mild Steel has a typical velocity of 5920 m/s. This means if you want to achieve the most accurate thickness measurements you must calibrate your thickness gauge to a sample of the same material you will be testing
Note: Your measurements are only as good as your calibration.
Note: Your measurements are only as good as your calibration.
Calibrating to known thickness – single point
This method of calibrating the gauge is more accurate than using a standard velocity value as the gauge calculates the velocity of sound for the sample material.
Calibrating to known thickness
The Two Point Calibration option is only available in Single Echo and Echo-Echo modes.
Two point calibration allows the gauge to be calibrated against two reference thicknesses of the same material, one at the minimum (thin) thickness range the other at the maximum (thick) thickness range.
Typically a Ladder Step Wedge is used to calibrate the probe and gauge for Steel. The ladder step wedge has 4 or 5 different thicknesses typically ranging from 2.5 mm to 20.0 mm. You would typically choose to calibrate using the 2.5 and 20 mm thicknesses.
