2Features: Non-contacting measurement Works with most materials High temperature measurementMicro Tensile Specimen measurement1 Laser diodes2 Cameras (CCD)3 Speckle Patterns4 Specimen
3Principles of Displacement Measurement with Laser Speckle Correlation The optically rough surface of a specimen reflects coherent light.Laser diode modules with a wave length of λ = 660 nm are directedtowards the specimen.The reflected light passing through the laser beam creates so-called„Speckle Patterns“.The image size of the CCD camera is called „Field of View“.Speckle = spot, dab or pointSpeckle PatternImage Size = Field of View (FOV)
4Principles of Displacement Measurement with Laser Speckle Correlation Requirements for displacement measurement with standard application:2 Cameras = 2 Speckle PatternsDistance between cameras = 50mmLenses … 75f x2 / 3,9 Fwith 2x extender we receivef=150mmWith these lenses a distance of 480 mmbetween specimen and cameras is possible
5This comparison is carried out up to twenty times per second. Principles of Laser Speckle CorrelationWhile cameras and laser modules remain in a fixed position, the surfaceof the specimen moves when extended.MasterSlaveTo measure the displacement of the surface, it‘s necessary to follow themovements of the Speckle Patterns.This is achieved by means of a cross-correlation algorithm comparing two successive patterns.This comparison is carried out up to twenty times per second.Measuring rate = 20 Hz
6The Speckle PatternThe size of the evaluated patterns can be set to up to 128x128 pixels.The cross-correlation (FFT) requires high computing capacity. ThereforePCs with a minimum CPU speed of 500 MHz are needed to reach measuringrates of 20 Hz.In order to measure up to 200Hz a 3 GHz Processor and High Speed DigitalCameras are required.
7The Correlation Peak The result of the cross-correlation is a function, where the positionof the maximum (Correlation Peak)corresponds with thedisplacement of the pattern.A special interpolation algorithmdetermines the position of thecorrelation peak in the subpixelrange and compensates for changesof the surface in real-time.Parameters for this interpolationalgorithm can be defined by the user.
8The peak is intersected by several planes parallel to the xy – plane.The results are sectional planeswhich are evaluated in twodimensions.The centres of gravity are regardedas the position of the peak.SWith this procedure it is possibleto reach a very accurate displacementmeasurements while saving a lot ofcalculation time.
9CalibrationCalibrating the LSE, the Speckle pattern must be moved for adefined stretch. This way the size of the FOVs (Field of Views) and theCalibration factors can be determined.This stretch can be as long as needed and adjusted in the LSE Software.The standard stretch for the calibration is 2 mm. The sample is mounted in onegrip only and shifted for exactly 2 mm.The size of the FOVs is calculated, the result saved and the LSE isready for measuring.If the distance between specimen and camera has changed, theLSE has to be re-calibrated.
10Features2 - dimensional strain measurement (longitudinal and transversal)
11FeaturesFeaturesDisplacement & 3 Point – Deflection Measurement
12Features Features Triangulation Sensor Head ME53-33 This application turning the cameras allows L0 setups from 0-250mm
13Features Features Triangulation Sensor Head ME53-33 applied to a Midi MachineTwo dimensional strain, multiple strainand deflection measurementTesting all kind of materials:MetalsPlasticsTextilesRubbers
14FeaturesFeaturesWorks with most materialsSteelAloyRubberPlastics
15FeaturesFeatures800° C high temperature measurement done in Australia, University of Technology in Brisbane
16Features Features compression test of all kind of material compression tests at high temperatures up to 1600 °C
17Features Features Laser Speckle Extensometer looking through temperature chamber glas windowilluminated specimen
18Features Features 0.1 µm resolution measurement of micro specimen Calibration by marks on the surface of the specimen