Stanford Linear Accelerator Center CMSC 2004, San JoseGGL, RR, BD 1
Investigations of Digital Levels for High Precision Measurements
Georg L Gassner
Robert E Ruland
Brendan Dix
Metrology Department
Stanford Linear Accelerator Center
Work supported by the U.S. Department of Energy under contract number DE-AC03-76SF00515
CMSC 2004, San JoseGGL, RR, BD 2
Stanford Linear Accelerator Center
Introduction
• Requirements at SLAC:– 150 m / 300 m– 50 m / single components
• Factors influencing the accuracy:– Scale factor– Critical distances and focusing– End section of the staff– Illumination
• Tested Equipment:– Leica DNA03– Trimble (formerly Zeiss) DiNi12– (Leica NA3000)
CMSC 2004, San JoseGGL, RR, BD 3
Stanford Linear Accelerator Center
Design and Hardware
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Stanford Linear Accelerator Center
Scale Determination
• Determination of the scale factor• Repeated regularly – ensures equipment works correctly
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Stanford Linear Accelerator Center
Critical Distances – Leica
• 1 code element (2.025mm) is projected onto exactly 1 pixel, or integer multiples
• Leica NA3000 critical distance at 14.92 m (causes up to 0.4 mm misreading)
• Leica DNA03 critical distance at 26.70 m
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Stanford Linear Accelerator Center
Critical Distances – DiNi12
• Size of 1 code element is 20 mm• Example: At 10.98 m 1 code element is projected onto 38
pixels• There are 251 critical
distances between 1.5 m and 15 m
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Stanford Linear Accelerator Center
Defocused Measurements
• Leica DNA03 and Trimble DiNi12: critical distances do not cause deviations > 30 m
• Defocused measurements increase these values
focused set up defocused set up
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End Section of the Staff (1)
• Measurements at the end section of the rod– Only parts of the staff are visible– Inaccurate measurements are the consequence
• Can also occur if parts of the rod are covered
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Stanford Linear Accelerator Center
End Section of the Staff (2)
• DiNi12– 300 mm code section– H [mm] = start of visible code on the staff + 150 mm
• Leica DNA03– DNA03 uses 1.1° code section (moveable)– H [mm] = start of visible code + 20 mm + 6.9·sighting distance [m]
invisible code section
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Stanford Linear Accelerator Center
• Only illumination at a steep angle
causes biased measurements of up to 100 m (only correct for the instruments tested)
Illumination
• Measurements in dimly lit environments require artificial illumination
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Stanford Linear Accelerator Center
Conclusion
• Determination of the scale factor on a regular basis gives the confidence of quality checked measurements.
• The level has to be horizontal and properly focused.
• When the highest accuracy is desired, the rod end sections and every obstruction have to be avoided.
• Illumination at a steep angle must be avoided.