You have to generally know the answer or have a priori knowledge from empirical data in order to measure the max deflection of the strain gauge or expansion of the tube. Pressure is an indirect measurement. The deflection is only measured along the finite length of the strain gauge. Seeing the tube is 3D and the measurement is pretty much 2D, I've often wondered how the location for the strain gauge was chosen. Maybe they knew where the majority of tubes had blown. I wouldn't think tube to be concentric, and the added effect only small, but why not choose a section somewhere else than the side, which is probably the easiest location for attaching the device.
Kind Regards,
Raimey
rse
