FOCUS 35 TOTAL STATION USER GUIDE
6 –
Instrument Technology
85
Correction for Collimation Errors
HA/VA Collimation
The horizontal collimation error is the deviation of the sighting axis from its required position at right
angles to trunnion axis.
The vertical collimation error is the difference between the vertical circle zero and the plumb axis of
the instrument.
Traditionally, collimation errors were eliminated by observing angles in both instrument faces. In the
Spectra Precision FOCUS 35 Total Station, a pre-measurement collimation test is performed to
determine the collimation errors. Angular measurements are observed in both instrument faces, the
collimation errors are calculated, and the respective correction values are stored in the instrument.
The collimation correction values are then applied to all subsequent angle measurements, including
the distance related focus lens collimation error. Angles observed in a single face are corrected for
collimation errors, which eliminates the need to measure in both instrument faces.
Carry out a collimation test in the following situations:
•
Whenever the instrument may have been roughly handled during transport.
•
When the ambient temperature differs by more than 10°C (18°F) from the previous collimation
test temperature.
•
Immediately prior to high precision angle measurements in one face.
Spectra Precision FOCUS 35 Total Station with LockNGo Tracker
A Spectra Precision FOCUS 35 Total Station with LockNGo capability can automatically lock and track
a prism target as it moves. Pointing errors caused by slight misalignment of the instrument’s tracker
have a similar effect to the HA and VA Collimation errors as detailed above.
To correct for the tracker collimation errors, carry out a LockNGo Tracker collimation test. The
LockNGo Tracker collimation test automatically observes angular measurements to a target in both
faces, the tracker collimation errors are calculated and the respective correction values are stored in
the instrument.
The collimation correction values are then applied to all subsequent angle measurements observed
when LockNGo Tracker is enabled. Angles observed in a single face are corrected for collimation
errors, which removes the need to measure in both instrument faces.
Carry out a LockNGo Tracker collimation test in the following situations:
•
Whenever the instrument may have been roughly handled during transport.
•
When the ambient temperature differs by more than 10°C (18°F) from the previous collimation
test temperature.
•
Immediately prior to high precision angle measurements in one face.
