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Autocollimator Calibration . Calibration : interpretation of output from Autocollimator Controller . What we have: Output from controller i.e. numbers that quantify the lateral displacment ( Δ x, Δ y) caused by tilts in arbitrary unit. What we search:
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Autocollimator Calibration Calibration : interpretation of output from Autocollimator Controller What we have: Output from controller i.e. numbers that quantify the lateral displacment (Δx, Δ y) caused by tilts in arbitrary unit What we search: A coefficient that transform the lateral displacment arbitrary unit in µm
Autocollimator Calibration The idea
Autocollimator Calibration Generate a tilt of a known angle Response spring Rotating rail Micrometric translation Micrometric translation stage + Rail arm = Known angle autocollimator
Autocollimator Calibration Procedure Step of T.S. 20 μm Min angle Δθ = 0,0571 mrad i.e. Δy=100 a.u. read Δy = 56.5 μm Lateral displacement Δy = 32 µm Average Δy read 74 measure of 20 μm step Δy = 56,783 a.u. Why this error?
Autocollimator Calibration Focal length Rail length Positioning (per step) Data Acquisition (per step) Average on100 meas St. dev. on 100 meas Difference between the two Y values Shift Angle Linear Shift Average of Conversion Coeff Difference between the two next angles
Autocollimator Calibration Next Step + Reduce Min. angle Δθ Improve Accurancy • Using Exapod • Using Theodolite+ large mirror