The Principle and Methods of Ultrasonic Thickness Measurement

Basic Principle
An ultrasonic thickness gauge measures thickness based on the principle of ultrasonic pulse reflection. When the probe emits an ultrasonic pulse that travels through the test material and reaches the boundary of a different medium, the pulse is reflected back to the probe. By precisely measuring the time it takes for the ultrasonic wave to travel through the material and return, the thickness of the material can be determined. This method is applicable to any material that allows ultrasonic waves to travel through it at a constant velocity.

H = v t / 2

H – Thickness; v – Sound velocity; t – Measurement time

二

Measurement Method
Explanation of Reference Labels:
A – Transmitting/Receiving Probe  A3 – Dual-element Probe
C – Ultrasonic Travel Time  D – Emission Pulse Signal
F – Interface Echo  E1, E2 – bottom Echoes
G – Delay Path  B – Test Sample

P-E (Pulse-Echo Method)
Measures the time between the initial pulse and the first bottom echo, with zero-point calibration applied.

I-E (Interface-Echo Method)
Measures the time between the interface echo from the delay block and the first bottom echo.

E-E(Echo-Echo Method)
Measures the time between two consecutive bottom echoes.

Tips

The appropriate instrument and measurement method should be selected based on the material, geometry, and thickness of the test object, as well as the required measurement accuracy. The accuracy of thickness measurement depends on the precision of the ultrasonic travel time measurement.