About kscrowe

The unit of the Y-Axis (Vertical) is 820 counts/g with a 0g position of 2048.  The BMI055 is mounted so the IC is facing toward the ceiling (up).  As you can see that on the left side the zero point is at roughly 1220 which is approximately 820 counts lower than 2048.  This equals 1g which is the effect of gravity.  This is when the z-axis offset register (0x3A) is zero.  Then on the right the at rest position is 2048 which is our 0g position.  This is done with the z-axis offset register (0x3A) is set to 1g.  Our application requires an output of 820 counts/g regardless of the range selected.  We handle this through a scale factor.   I think this is getting a bit off track.  What we have here is two identical tests.  The left side has the z-axis offset register (0x3a) at 0g.  The right side has the z-axis offset register (0x3A) at 1g.  Why is the data output from the IMU so different between these two scenarios.  And what does the BMI085 offer to correct the effects of this asymmetric railing problem given that the register has been removed.   This is becoming even more critical for us.  We know that having this register at 0g causes problems in our application.  We have just been informed by a Bosch representative that we cannot procur any BMI055 allocation for 2022.  We are looking into migrating to the BMI085, which is why I started this thread.  We need to know how to migrate to the BMI085 and how to deal with asymmetric railing on the BMI085 part given that the solution we have used in the past on the BMI055 has been removed.   ... View more

I was able to obtain the source files.  Here are some higher resolution images.  The range was 16g.  Although all ranges have been tested and all ranges experience the problem.  16g has less problems than the lower ranges, but the problem is still there regardless. ... View more

Here is the data that shows the issue.  Unfortunately, I do not have access to the source files but this should demonstrate the issue.  In the graphs the vertical and horizontal scale are the same for each tick, but it is hard to read.  The top graphs are with the Z-Offset register set to 1g in the BMI055 and the lower graphs are with the Z-Offset register set to 0g.   The test involved setting up two BMI055 on the same mechanical member.  Then the member was struck producing an impulse response.  All BMI settings are the same for both IMU's except for the Z-Offset register.  There are three graphs.  The baseline is the captured output from the IMU.  Then the medium filtering applies some filtering using a moving average algorithm.  The heavy filtering applies even more filtering.  As you can see when the Z Offset register on the BMI055 (top graphs) is set to 1g the response to this input is much better.  In our application we also see significant improvement in performance when having the Z Offset within the IMU. The bandwidth of the IMU's would be 15.63Hz.  I am unsure of the range, but both would be configured the same.  Due to processing limitations in our application the bandwidth must be 15.63Hz.   ... View more