The backwall echo evaluation-threshold can be positioned very close to the interface echo. Even the interface echo waves are within the backwall echo threshold, but not exceeding. This is to take care in automatic testing, should not be less than 6-10 dB. Thin wall thickness condition with a limitation of evaluation possibilities. The limitation is due to the last interface echo wavecurves. Small outer diameter, interface echo amplitude is smaller than backwall.
Condition is acceptable but interface echo can be improved with use of focused transducers.
Small outer diameter and very small wall thickness. The thin measurement capability is highly improved due to small interface echo amplitude. Good signal condition. Interface echo amplitude is higher than backwall echo amplitude. Backwall echo attenuation and frequency shift to lower frequency.