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Total Station Instrument Errors

leica-builder-total-station

A total station is a highly accurate instrument. Temperature changes, vibrations, and long transport periods can all affect your instrument’s accuracy. Therefore, you must compensate for these changing conditions when you set up your total station. If you want to measure in just one face, then immediately before the measurements you must determine the instrument errors and store them.
 
Ideally, the total station should meet the following requirements:

  • Line of sight ZZ perpendicular to tilting axis KK
  • Tilting axis KK perpendicular to vertical axis VV
  • Vertical axis VV strictly vertical
  • Vertical-circle reading precisely zero at the zenith

 
If these conditions are not met, you will see any of four error messages. Don’t panic. Here’s what they mean.

Line-of-sight error c (Hz collimation): deviation from the right angle between the line of sight and the tilting axis.

Tilting-axis error a: deviation from the right angle between the tilting axis and the vertical axis.

Taking measurements in both telescope faces eliminates line-of-sight errors and tilting-axis errors. You can determine and store both the line-of-sight error and, for highly precise total stations, the tilting-axis error, which is generally very small. The total station will then automatically take these errors into consideration whenever you measure an angle. That means your measurements will be practically error-free, even using only one telescope face. Check your user manual for specifics on how to determine and store these errors.

Vertical-axis tilt: angle between plumb line and vertical axis

Vertical-axis tilt is not an instrument error. If you don’t level up the total station properly, you won’t be able to eliminate the error in both telescope faces. The internal compensator automatically corrects its effect on measuring horizontal and vertical angles.

The larger the height difference between your target points, the greater the influence these three errors will have on your horizontal angle measurements.

 
Height-index error i (V index): the angle between the zenith direction and the zero reading of the vertical circle; that is, the vertical-circle reading when used as a line of sight. It is not 100 gon (90 degrees), but 100 gon + i.

By measuring in both faces and then averaging, the index error is eliminated; it can also be determined and stored.

Once you level up your total station, determine any errors caused by atmospheric conditions and handling, and store those errors, you’re good to go!

Give us a call with any questions you might have about total station error calibration. If you prefer to learn hands-on, we also offer in-house and on-site training.