High Temperature Thin Film Strain Sensor Calibration and Mounting
High temperature thin film strain sensor accuracy depends on rigorous apparent strain polynomial correction, dielectric barrier integrity, and drift mitigation.
Laser Interferometric Extensometer
Optical Measurement
Non-contact optical displacement instrumentation measures relative surface displacements on structural specimens subjected to mechanical or thermal loading. A laser interferometric extensometer splits a coherent laser beam to illuminate two distinct target points or indentations on the specimen surface. Reflected light recombines to generate interference fringe patterns that shift in direct proportion to gauge length changes.
Sub-nanometre displacement resolution enables accurate strain determination across microscale and macroscale gauge lengths. The instrument functions without mechanical contact, eliminating mass loading and high-temperature knife-edge slippage errors.
Optoelectronic Design
Helium-neon or solid-state laser sources provide stable wavelength references for interference fringe generation. Beam-splitting optics direct illumination paths, while high-speed photodetector arrays capture dynamic fringe transitions. Dual-beam tracking architectures compensate for rigid-body specimen motion within the measurement volume.
Phase-shifting electronics convert optical intensity variations into high-resolution displacement readings in real time. Optical access requirements necessitate environmental chambers with anti-reflection coated quartz viewports.
Thermal Stability
Furnace air turbulence creates index-of-refraction gradients that distort optical path lengths and induce apparent displacement noise. Enclosing optical paths in protective tubes and applying digital filtering suppresses environmental air convection noise. Specimen thermal expansion changes surface reflectivity, which requires automatic detector gain control.
Thermal incandescence at temperatures exceeding eight hundred degrees Celsius is eliminated using blue laser sources and narrow bandpass optical filters. Frame mounting must isolate the optical head from mechanical vibrations originating from load frame hydraulics.
Calibration Boundary
Measurement validity depends on precise calibration of the initial optical gauge length between illumination target points. Specimen out-of-plane tilting generates cosine errors that falsely inflate or reduce calculated axial strain values. Surface oxidation or spallation during high-temperature testing disrupts speckle patterns and causes optical signal dropouts.
The instrument requires initial alignment verification using certified micrometer stages traceable to national standards. Maximum trackable strain rate is constrained by the photodetector sampling frequency and fringe counting electronics.