I have bought an STM iNEMO evaluation board in order to monitor the inclination of a separate magnetic sensor array as it moves in a linear scan outside of a (non-magnetic) stainless steel pipe. I want to measure the inclination of the sensor along the scan and ensure that it does not change. The problem I have found is that the measured magnetic field from the integrated magnetometer varies greatly with position along the pipe, and in turn, causes a large, position dependent error in one axis of the inclination reported by the iNEMO IMU. In fig. 1 below I show the set up of the test, I measured the inclination from the IMU while moving it along the length of the pipe and back again. The board did not change inclination throughout the measurement. In Fig 2 I show the magnetometer and inclination measurements recorded by the "iNEMO application" showing the large error in one of the inclinations.
My question is whether you know if there is any way of correcting for the magnetic field variation so that I can still accurately determine the inclination in all three directions? My data suggests to me that the magnetic field variation measured from the magnetometer is much greater than the geomagnetic field, so the inclination measurement will always be inaccurate. A follow up question I then have is: Is there a way to measure 3 axis orientation WITHOUT using a magnetometer?