Mount the IMU
Mount the IMU in a fixed location where the distance from the IMU to the GNSS antenna phase center is constant. Ensure that the orientation with respect to the vehicle and antenna is also constant.
For attitude output to be meaningful, the IMU should be mounted such that the positive Z-axis marked on the IMU enclosure points up and the Y-axis points forward through the front of the vehicle, in the direction of track. If the IMU is not mounted in this orientation, a rotational offset must be applied. See Rotational Offsets for more information.
Also, it is important to measure the distance from the IMU to the antenna (the Antenna Lever Arm), on the first usage, on the axis defined on the IMU enclosure. See Lever Arm Calibration Routine. See also IMU Technical Specifications for dimensional drawings of the IMU enclosures.
Ensure the IMU cannot move due to dynamics and that the distance and relative direction between the antenna and the IMU is fixed. See SPAN Configuration.
The closer the antenna is to the IMU, particularly in the horizontal plane, the more accurate the position solution.
Also, your measurements entered using the SETINSTRANSLATION command must be as accurate as possible, or at least more accurate than the GNSS positions being used. For example, a 10 cm error in recording the antenna offset will result in at least a 10 cm error in the output. Millimetre accuracy is preferred.
The offset from the IMU to the antenna, and/or a user point device, must remain constant especially for RTK or DGPS data. Ensure the IMU, antenna and user point device are bolted in one position perhaps by using a custom bracket.
Securing the IMU Enclosure
The IMU Enclosure (IMU-ISA-100C, IMU-LN200, IMU-LN200C, IMU-HG1900 and IMU-µIMU-IC) can be secured directly to the mounting surface or can be secured using the IMU Enclosure Mounting Plate.
To secure the IMU Enclosure directly to the mounting surface, use four M6 screws that pass through the mounting surface and into the bottom of the IMU Enclosure. For the location and spacing of the mounting holes, refer to the mechanical drawings of the IMU in IMU Technical Specifications.
The optimal screw penetration into the IMU Enclosure mounting holes is 5.0 to 6.0 mm deep. When selecting screws for mounting the IMU Enclosure, ensure the screw penetration does not exceed 6 mm. Using excessively long screws can damage the IMU Enclosure.
The mounting screws should be torqued to 42 to 45 in-lbs.
For information about securing the IMU Enclosure using the mounting plate, refer to Secure an IMU Enclosure Using the Mounting Plate.
Other IMUs are secured using the four through holes in the base of the IMU.