Transcript Sec10_Digital_Level_Calib.ppt

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
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 1
Introduction
• Requirements at SLAC:
– 150 mm / 300 m
– 50 mm / 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)
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 2
Design and Hardware
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 3
Scale Determination
• Determination of the scale factor
• Repeated regularly – ensures equipment works correctly
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 4
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
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 5
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
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 6
Defocused Measurements
• Leica DNA03 and Trimble DiNi12: critical distances do not
cause deviations > 30 mm
• Defocused measurements increase these values
focused set up
defocused set up
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 7
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
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 8
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
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 9
Illumination
• Measurements in dimly lit
environments require
artificial illumination
• Only illumination at a steep angle
causes biased measurements of
up to 100 mm (only correct for the
instruments tested)
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 10
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.
Stanford Linear Accelerator Center
CMSC 2004, San Jose
GGL, RR, BD 11