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.