Trimble RTS - Field Collimation (HA/VA)

The collimation routine consists of the HA/VA collimation and then the trunnion axis tilt.

The Horizontal and Vertical collimation and the trunnion axis tilt correction have been

measured and stored in the instrument at the factory.

The S Series Total Station instrument utilizes precise angle and distance measurements to

determine the position of the point being measured. The instruments design facilitates the

ability to measure all points with a single pointing to the target in the Face I position. All

electronic total stations are subject to collimation errors in both the horizontal and vertical

angle measuring systems, and also errors caused by the axis of the telescope not being truly

perpendicular to the vertical of the instrument.

In order to compensate for these errors, the collimation routine allows the operator to

accurately determine the current errors in the instrument, and store the errors as corrections to be applied to all measurements made in a single pointing to a target. In this way the S Series Total Station will always provide accurate measurements.

The Collimation errors and Trunnion axis tilt will change over time, the commonest changes

being caused by:

• Wear and tear with use
• Bumps and knocks during transit
• Large changes in operating temperature

Trimble recommends that a collimation check and tilt-axis check be carried out routinely as

follows

• After any long uncontrolled transport of the instrument (e.g. after service or shipment to a
  new location)

• After any accidental knock or drop
• At any time when the operating temperature changes by more than 10 •C (18 •F)
• At any time when the instrument changes the height above sea level by more than 500m

(1640 Feet)

• At any time when the highest precision positions are required
• Routinely on a periodic basis (Monthly, weekly etc.)

Trimble also recommends that the operator keep a record of the dates and values measured so that any gross changes can easily be detected. Gross changes can indicate the need for a

check by an approved service center.

In all calibrations, multiple sightings will be made in both faces to ensure that any minor

pointing errors can be eliminated in the accurate determination of current collimation error

values.

In a new instrument the values should be close to zero, over time these will change. The

instrument allows a maximum value of 0.05 grads (0.045 degrees) in the HA, VA and

Trunnion axis tilt values. If these values are exceeded, the instrument will need a service to

rectify a mechanical problem.

Field Collimation Routine

1. Press to scroll to HA/VA collimation and then press
   1. The current collimation values appear
2. Press to scroll to one of the following:
   1. Continue. Then press to continue the HA/VA collimation test.
   2. Abort. Then press to return to the Adjustments menu.
   3.  
3. If you select Continue: Press to scroll to one of the following:
   1. New Observation. Then press to continue the HA/VA collimation test.
   2. Switch Face. Then press to change between face 1 and 2.
   3. Abort. Then press to return to the Adjustments menu.
4. If you select New Observation:
   1. Aim accurately in face 2 towards a point near the horizon at max. ±5 grads (±4.5 degrees) to the horizontal and at a minimum distance of 100 m (328 ft.).
   2. Press to measure and record angles.
   3. Re-sight the instrument at the same point and press the enter key again. Repeat this process for a minimum of 5 sightings in Face 2.
   4. Press to scroll to Switch Face. Then press  to change to face 1.
   5. Aim accurately towards the same point as that used in face 2.
   6. Press  to measure and record angles.
   7. Re-sight the instrument at the same point and press the enter key again. Repeat this process for the same number of times as in Face 2.
      1. As observations are made on the first face (either face 1 or face 2), the angle values are stored and the counter increases. When one or more observations have been taken on each face, and the number of observations on each face are the same.
   8. The software calculates and displays the new horizontal and vertical collimation values.
5. Press  to scroll to one of the following:
   1. Trunnion Coll. Then press to continue to Trunnion collimation.
   2. Store Correction. Then press  to accept and store the new collimation values.
   3. Abort. Then press to return to the adjustments menu.
   4. 
6.  Press Select Trunnion Coll. to continue with trunnion axis tilt collimation. Press to scroll to Trunnion Coll. Then press to continue the Trunnion axis tilt collimation test.
   1. 
   2. 
7. Press to scroll to one of the following:
   1. New Observation. Then press to continue the trunnion axis tilt test.
   2. Switch Face. Then press to change face.
   3. Abort. Then press to return to the adjustments menu.
8. If you select New observation the number of observations in both faces appears:
   1. Aim accurately in face II towards a point at least 15 grads (13.5 degrees) above or below the point where the collimation test was made at a minimum distance of 30 m (66 ft.).
   2. Press to measure and record angles.
   3. Press to scroll to Switch Face. Then press to change face.
   4. Aim accurately towards the point.
   5. Press to measure and record angles

      1. As observations are made on the first face (either face 1 or face 2), the angle values are stored and the observation counter increases. When one or more observations have been taken on each face, and the number of observations on each face are the same, the software calculates and displays the new trunnion axis tilt value.

      2. 
9. Press to scroll to one of the following:
   1. Store Correction. Then press to accept the new trunnion axis tilt value.
   2. Cancel. Then press to return to the adjustments menu.

Note –The instrument will prohibit a trunnion axis tilt test if it is made towards a point with an angle less than 15 grads (13.5 degrees) from the point where the collimation test was made. The trunnion axis tilt determination accuracy will improve with a steeper angle towards the measured point. The minimum distance for the trunnion axis tilt measurement is 30 m (66 ft.).

Note – If the trunnion axis tilt correction value is greater than 0.05 grads (0.045 degrees), the message Fail Remeasure? appears. Press Yes and then repeat the measurement procedure. If the value is greater than 0.05 grads (0.045 degrees) and you answer No to the premeasurement message, the instrument uses the correction value previously stored in the instrument. If the value is greater than 0.05grads (0.045 degrees), then the instrument must be mechanically adjusted at the nearest authorized Trimble service center.