ABSTRACT

The difference between resolution and accuracy is highlighted with respect to ultrasonic thickness gauges. After briefly describing the principles of operation, sources of errors are discussed, and where possible quantified. It is shown that calibration to national standards has no place in this field.

It is concluded that while the thickness gauge is a valuable tool for routine inspection, the accuracy of its readings should not be accepted with unquestioning faith.

Table of contents Full Text


1. Introduction
   Accuracy and Resolution, The digital time of flight gauge, What is calibration?
2. Principles of Operation
   Obtaining a Time of Flight, Converting to Thickness
3. Sources of error
   Time of Flight errors, Variations in speed of sound, Temperature
4. Conclusions