Are there any app notes on how to integrate the rate signal of a ADXRS649 to obtain an angular position?
I apologize for the gap in ADI's reply to this post. We have all been on business travel and are still new to managing an online forum, so I hope that you can forgive us. While we do not have any application notes for this specific topic, we can certainly help you. Before we start down the steps required for this, what have you done so far? Here are the steps to achieving this, for a prototype. Your accuracy/stability goals will dictate the complexity associated with the process.
In a continuous time system, the angle displacement is equal to the integration of the angular rate.
Once you have an accurate digital representation of the angular rate, you can use a summation function to integrate the rate output and produce an angle displacement estimate.
The following FAQ post provides an example of this calculation, in the attached Excel file.
For gyroscope calibration, you might find the following information to be helpful:
I hope that this helps. We look forward to hearing about your progress and next questions.
After a few weeks delay, we are now back on this project. A circuit is prototyped and running. The integrator is noisy as would be expected on a breadboard. It needs to be a PWB with guard traces and the like to address the cap leakage and low noise requirements for the integrator. We are trying to obtain 0.1 degree resolution.
But my latest question is regarding to component specs. The data sheet for the ADXRS640 list the following sensitivity spec: 0.08 to 0.12 mV/degree/sec initial and over temp.
This is quite a spread (20%). Is most of the variation due to temp change or inherent baseline sensitivities from part to part?
With this much variance we would have to have an involved calibration procedure to take everything into account.
The sensitivity change over temperature is small +/-2%. We specify this parameter as "Sensitivity Temperature Drift" in Table 1 of the datasheet. As far as part to part variation - the min/max numbers for sensitivity represent mean +/-3*sigma. A typical population will be much tighter, you can refer to Figure 8 in the datasheet for a distribution of sensitivity at 25C.
Another question. The ADXR649 data sheet says the measurement range can be extended to 50,000 degrees/sec by adding a 120kohm resistor between RATEOUT and SUMJ. Can the range be reduced to +-7200 degrees/sec to enable the full output range of the device to be used for a slower speed?
The range can only be increased and not lowered.
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