PhidgetSpatial 3/3/3 - Inconsistent tilt or pitch measure?

Hello,
I use PhidgetSpatial 3/3/3 to measure the pitch.
I use also an inclinometer Disto D8 from Leica as reference.
Both devices are laid on perfectly horizontal board mounted on tripod used by photographers.

This is my methode to calculate the pitch:

  • Read all 3 axes of acceleration then normalize all 3 accelerations.
  • Pitch = arcsin(accelerationY) *(180 / PI);

Tilt my board up /down.

The pitch results in degrees:

Disto Phidgets

-60 -58.7
-50 -49.1
-40 -39.4
-30 -29.7
-20 -20
-10 -10.4
0 0.3
10 9.1
20 18.6
30 28.3
40 38
50 47.7
60 57.6

As you can see, at 0, Phidgets gives 0.3
The range “up direction” [0,60] gives differents result from range “down” [0,-60].
Range [0,-60] is closer to the expected values but it’s not accurate.

How can I use this Phidgets reliably ?
Internally calibrated at the factory
Rigorously tested to ensure “real life” data
This is what I read in Phidgets marketing website.

Can I trust data coming from this board ? I think I don’t need a calibration as the device is calibrated at the factory.

What is the typical error range / precision of this board in “real life” ( 300μG ?)?

Hello Yaumas,

The discrepancies between the readings do not seem to be statistically significant. We suggest you use the same number of significant digits in both measurements in order to obtain a better comparison between the two sensors. You might also want to filter the Phidget readings using a moving averagein order to smooth the results.

Also, keep in mind that you formula for the pitch is incomplete since it does not take into account all of the other acceleration axis.

Finlay, since you sensor is also a 3-axis magnetometer and 3-axis gyroscope, you might want to use those extra readings in order to obtain more accurate readings. For instance, using the gyros for obtaining the roll, pitch and heading is prefered as long as the drift is compensated by using the magnetometers and accelerometers