MPL3115A2 altitude variability

[miribelgart]

Hi all,

We are using MPL3115A2 on a custom board to measure altitude differences between devices.

I have read all the Q&A I could find on this forum regarding issues with altitude measurement, but I am still not sure if what I am seeing is considered normal or not (using one-shot mode with 128 OSR, sampling at 1Hz):

1. The variability between consecutive samples (1 second apart) seems pretty big. The board is stationary, on a desk inside a small cardboard box to block out light. Within 5 minutes of sampling I get altitude between -6.1875m and -8.8125m, the average being -7.22m. There were no changes in the room during this time, no A/C or doors/windows opening or closing. Is this normal or is there a way to improve these results? Could this indicate a faulty sensor? Full log attached.

2. There seems to be a big difference between readings of different sensors: 3 sensors working simultaneously in the same conditions show averages of around -7m, 10.3m and 6m. Is this a matter of factory calibration that I should solve using OFF_H, or does this indicate that the sensors were harmed during soldering?

Thanks!

Miri

Original Attachment has been moved to: altitude.txt.zip

[david_diaz]

Hello Miri,

The errors of the NXP integrated pressure sensors, are minimized by calibration and compensation done after assembly, and before the gel fill operation. However, because of slight variations in fabrication, every device is produced with a unique temperature characteristic. Both the magnitude and the sign of the temperature coefficient are variable from unit to unit. The best way to get higher accuracy is to calibrate each sensor at multiple temperatures.

My recommendation is:

If you know your current position and the altitude using some external calibration point in meters, then adjust the OFF_H register (0x2D) to account for the discrepancy.

The 2’s complement offset correction registers values are used to trim the temperature, altitude and pressure offsets that might occur over the life of the product.

Please let me know if the issue remains besides these recommendations.

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know.  I will be glad to help.

Have a great day.

David Diaz.

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