Chapter 3
Theory of Operation
P/N 57150002, Revision 5.0 3 - 41 Trimble S, VX, SPS & RTS Service Manual
F
Automatic correction of angle values
In addition to the fast acquisition of accurate angles, the angle measurement system compensates for
the following:
• Automatic correction for deviation of the plumb axis.
• Automatic correction for collimation errors (HA/VA collimation & Tracker collimation).
• Automatic correction for trunnion axis tilt.
• Arithmetic averaging for reducing sighting errors.
Automatic correction for deviation of the plumb axis
Deviations in the plumb axis may occur when one (or more) of the tripod legs move as a result of
unstable ground or changes in ground viscosity, such as the heating of road tarmac. Corrections for
this movement are essential to ensure that accurate measurements are obtained.
In contrast to most total stations, MagDrive allows the Trimble S6 to correct not only the horizontal
and vertical angles for mislevelment, but also the aiming errors caused by mislevelment. The
mislevelment correction is applied to the servo drive to re-aim the instrument. For example,
correcting the aiming when extending a vertical line to ensure that a true vertical line can be obtained.
The result is that horizontal and vertical angles are corrected for mislevelment while the instrument
is accurately aimed at the correct location. This ability ensures that mislevelment errors are corrected
to provide accurate angle measurements.
Automatic correction for collimation errors (HA/VA collimation & Tracker (Autolock)
collimation)
Collimation errors affect measured horizontal and vertical angles. The horizontal collimation error is
the difference between the line of sight and the plane perpendicular to the trunnion axis; the vertical
collimation error is the difference between the vertical circle zero and the plumb k s. Traditionally,
collimation errors were eliminated by observing angles on both instrument faces. In the Trimble S6
the collimation errors can be predetermined by performing a pre-measurement collimation test.
Angular measurements are observed on both instrument faces to enable the collimation errors to be
calculated and the respective correction values to be stored in the instrument. The collimation
correction values are then applied to all subsequent angle measurements. Angles observed on a single
face are therefore corrected for collimation errors, thereby removing the need to measure on both
instrument faces.
Trimble S6 instruments with Autolock technology can automatically lock and track a target. Since
the sighting to the target is performed by the instrument, the affects of horizontal and vertical
collimation are similar to those experienced during manual sighting. To correct for the collimation
errors in the tracker unit, an Autolock collimation test can be performed.
The Autolock collimation test automatically observes angular measurements to a target on both
instrument faces. The Autolock collimation errors are then calculated and the respective correction
values are stored in the instrument The Autolock collimation correction values are then applied to all
subsequent angle measurements observed when Autolock is enabled. Angles observed on a single
face are therefore corrected for collimation errors, thereby removing the need to measure on both
instrument faces.
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