Pole bias adjustment

This topic applies to only Trimble receivers which have a built-in IMU sensor.

When using IMU tilt compensation, Trimble recommends using an undamaged carbon fiber range pole in excellent condition. The quick release should also be in optimal condition with no damage to the mating surface between the receiver and the quick release.

The pole bias adjustment corrects errors introduced when using a pole that may have become damaged during normal use and is no longer perfectly straight, or if the pole tip is no longer true and perfectly aligned with the center of the pole. Pole bias adjustment should be performed in optimal RTK environment with a good IMU alignment.

The pole bias adjustment takes one set of measurements while facing one direction, and then a second set of measurements after rotating the receiver 180 degrees. It then calculates the corrections to correct for any errors introduced by the pole.

Trimble recommends that you perform the pole bias adjustment:

  • When the receiver is using a pole and quick release in sub‑optimal condition.
  • Each time you change to a different sub‑optimal pole.

The pole bias adjustment affects IMU tilt compensation measurements only. In GNSS‑only mode, make sure the pole is straight, has a calibrated physical spirit level vial and an accurately calibrated GNSS eBubble.

  1. Attach the receiver to the pole.

  2. Set up the receiver on a well defined point, with or without a bipod. The pole tip cannot move during the routine so it is best to place it on a control point or other stable and indented point where the tip of the rod can positively rest throughout the routine.

  3. Turn on the receiver and connect it to Trimble Mobile Manager.

  4. To open the Pole bias adjustment screen, tap and select Calibration. Tap Pole bias adjustment.
  5. Enter the Antenna height in meters. The height must be greater than 1.5 meters when performing a pole bias adjustment.
  6. If the GNSS correction status field shows Waiting then the IMU is not aligned. In good RTK environments the IMU reliably realigns itself automatically during natural pole movement. To align the IMU, rock the pole back and forth while keeping the pole tip on the ground, or walk a short distance (generally less than 3 meters) while changing direction a few times.

  7. When the GNSS correction status field shows OK. tap Pole bias adjustment to start the pole bias adjustment routine.

    During the pole bias adjustment, keep the pole vertical and stationary and the pole tip in the same location on the ground while the measurements are recorded. If you are not using a bipod make sure you hold the receiver as stable as possible.

  8. Tap START. Step one of the adjustment begins. Follow the instructions for each step very carefully.

  9. When step one is complete, rotate the receiver 180° without moving the pole tip, and press Start to begin step two.

  10. Tap Store to apply the correction values.