Optical Coherence Scanning Measurement Limit Boundaries on Vertical Tooling Cavity Sidewalls
Side-viewing prisms and polarized optical coherence gating extend sidewall slope scanning limits beyond eighty-five degrees in deep tooling cavities.
Phantom Wall Reflection
Meaning
Spurious signal artifact occurring in non-contact optical metrology where light reflects from an internal or back surface and is mistaken for the primary front surface. This phenomenon is common when measuring the wall thickness of transparent or translucent plastic parts like medical tubing or clear containers. The secondary reflection creates a ghost image that can confuse the software, leading to a thickness reading that is double or half the actual value.
Signal Discrimination
Sophisticated algorithms are used to filter out these secondary echoes by analyzing the intensity and timing of the return pulses. The phantom wall reflection of a clear resin part must be identified and ignored to ensure that the automated inspection system provides a valid measurement of the outer diameter.
Material Clarity
Degree of interference increases with the transparency and the refractive index of the polymer. In opaque or highly filled resins, the light is scattered before it can reach the back wall, which naturally eliminates the problem of ghost reflections.
Measurement Reliability
Correct calibration of the sensor involves setting gates that only accept signals within a specific expected range. This setting ensures that a phantom wall reflection does not trigger a false alarm or hide a genuine thin spot in the material.