Hello!
We regularly use the ICM-20948. We find it very helpful, but notice that the timestamps can often be inconsistent or erratic, which is causing problems in our application (high-precision synchronization with a 200 Hz camera).
For example, the sample rate should be 110 Hz according to the documentation, but we find that it fluctuates and can spend significant time sampling at 142 Hz and then it can switch to 83 Hz.
Here is an example distribution (also uploaded as attachment), showing the frequency of inter-sample intervals between successive IMU datapoints. If the device always measured at 110Hz, then the time between IMU samples should be ~9.09 nanoseconds, but it is almost never this:
In our tests, it spends about 1/3rd of time at 110Hz, 1/3rd of time at 142Hz and another 1/3rd of time at 83Hz.
We also find that timestamps can be duplicated. That is, the same timestamp repeats for different data samples.
It can even briefly go as low or as high as 55 Hz or 250 Hz, as shown by the red bars in the above plot.
On average, we usually measure about 105 Hz or 114 Hz across a sample of ICM-20948 units, so not exactly 110Hz.
Is this known? If so, is there a certain combination of settings or a power requiremnt that is needed to achieve a consistent 110 Hz sample rate? How did you measure it in the factory?
Many thanks and best regards,
Rob
I hope it is alright if I raise this question again. Thanks!
- Rob