High-Speed Measurement of the Internal Diameter of Tubes: A Comparison of Methods

The authors have compared various methods of tube measurement and have made the striking conclusion that the continuous measurement of the internal diameter of precision tubes with an air gauge is often useless in practice. The methods selected for experiment were all contactless and so included only air-gauging techniques and the capacitive measurement system. The authors propose an improved air-gauging technique where the pressure transducer is close to the air nozzles thus increasing the measurement speed by 12 times. However, the capacitive method was found to be even faster as well as stable and accurate. The disadvantage with the capacitive method is the need to introduce a probe into the tube. This difficulty is avoided by an indirect method where both external diameter and wall thickness were found instead and the difference taken. The perfected system has now been combined with ultrasonic immersion testing for flaws to make a complete tube testing facility.