Design and performance of a non-contact AF tester

Many Nitinol applications require the accurate measurement of shape recovery properties. A commonly used method for the determination of transformation temperature, using a displacement transducer (LVDT or RVDT) to plot the diameter of the part with respect to the temperature, is limited. Problems with this method stem from the force exerted on the probe, geometry difficulties in fixturing the part, and the limited size range over which the transducer can effectively measure displacement. A non-contact system using instruments such as laser micrometers or machine vision systems can measure the mechanical transformation without the aforementioned limitations. Non-contact A(f) measurements have been made using a CCD camera-based machine vision system that records the displacement of the part digitally in pixels as opposed to a voltage signal.