I am writing my master thesis in a company on aerospace and its applications. We are currently working on MEMS sensors and I have a tool to run the performances of MEMS sensors based on the specifications and a model that has been developed. I am currently on analysing the performance of Bosch accelerometer and gyroscope products.
Based on my model and definitions, I am currently having a few confusions with the data sheets for the sensors. I will ask for both accelerometer and gyroscope. They will be like in the following;
Questions for BMG160 gyroscope;
1) I see on the data sheet that the ‘senstivity’ value has a unit of LSB/°/s. Is this parameter corresponding to scale factor, as an effect on the input/output ratio of the device? If so, how can I convert this to a unit of %(divide by 8 maybe?)? If not, which parameter value shall I use as a scale factor for my calculations available in the data sheets?
2)I see ‘cross axis sensitivity’ parameter. Is this parameter the same thing with the non-orthogonality of the 3-axis? If not, can I have a detailed definition for that parameter?
3)On the data sheet, I can’t see the misalignment error of the sensors(3 gyroscopes). Is this error considered on the model or is it given as a different parameter or calculated differently? My main consideration is to distinguish the non-orthogonality of the 3 axis measurements and the misalignment of the 3 different sensors because I have different parameters for both in my model.
Questions for BMA400 accelerometer;
1)Similar to the above case, which parameter shall I refer to as the scale factor?
2)What exactly is the ‘Alignment Error’?
3)Why is the unit for the non-linearity ‘%’ ? Shouldn’t it be a function of the true acceleration?
4)Also similarly to the above case, is there a term for the misalignment of the sensors (with respect to each other) in the sheets?
The documents I am referring are BST-BMG160-DS000-09 revision 1.2 and BST-BMA400-DS000-02 revision 1.1 .
Thank you for your time and I am looking forward to hear from you soon.
Solved! Go to Solution.
--Similar to the above case, which parameter shall I refer to as the scale factor?
The parameter sensitivity can be taken as the scale factor. And please note that the range of this parameter can be calculated as: in 2g range, (Value_max/min – Value_typical)/Value_typical, here is (1065-1024)/1024= 4%; (983-1024)/1024=-4%, so in summary +/- 4%
--What exactly is the ‘Alignment Error’?
The alignment Error is refer to the direction mis-alignment between the MEMS(sensing part) and the package outline. so the real detecting direction of the X,Y can be a slight different from mounted direction(outline package).
--Why is the unit for the non-linearity ‘%’ ? Shouldn’t it be a function of the true acceleration?
the non-linearity can be calculated/measured: max(output_measured – output_expected) / full-range , so this is why the unit is %
--Also similarly to the above case, is there a term for the misalignment of the sensors (with respect to each other) in the sheets?
The min/max value of each parameter represent the 3σ, which means 99.73% sensors are within the (u-3σ, u+3σ) range, so this can be taken as the difference between sensors.
And the non-orthogonality seems more like alignment error.
Thank you for the clarifications! Now I can read the data sheet in a better way. Only another question is that on the data sheet, I can't see the min and the max values for the sensitivity and non-linearity, I only can see the typical values. How can I obtain the min and max values in this case?Also, how can one obtain turn on-turn off bias and the bias in-run stability?
This data is measured but not publicly available. Please contact your local sales representative to learn more.
You can calculate the minimum/maximum scale factor in the following way:
Scale factor error (sensitivity error) = |min/max – typical|/typical
Can you elaborate on the bias and bias instability? We actually have parameters named 'zero-g offset' and 'zero-g offset temperature drift'.