Precision with MPXA6115A for an altimeter application

[baptistethomas]

Hi,

I plan to use the MPXA6115A for an altimeter application. This device is suggested in the datasheet for this kind of application.

When I calculate altimeter precision from the datasheet, result is very bad.

Sensor is given for +/-1,5%, for my application I've to apply a temperature factor of 2,5, so for the full scale of pressure the accuracy is +/-3,75%.

+/-3,75% corresponds to a +/-37,5hPa.

The range of the altimeter I hope to do is from 0 to 2000m correspondig to a pressure of 1013,25 to 800 hPa (only a part of the sensor range).

On this range, altitude and pressure could be considered as linear.

I want to detect a 1100m threshold corresponding to 888hPa.

888hPa +/- 37,5hPa corresponds to about 1100m +/-350m. Error I can have on the sensor impact considerably the altitude.

To have a good accuracy on altitude, is it necessary to calibrate the sensor ? if YES, what do you advice ?

What solution exist to reduce this error and how this error is divided (offset, linearity, hysteresis, offset drift with temperature, linearity drift with temperature...)?

I hope to have an accuracy of about +/-20m (worst case +/-50m)

I know that digital sensor exist with a better accuray but analog sensor must be used in my application.

Best regards

[david_diaz]

Hello Baptiste,

Thank you for writing to the NXP communities.

This overall accuracy parameter for integrated pressure sensors consists from following main contributing errors:

1. Offset
2. TCO (temperature coefficient of Offset)
3. Linearity error
4. Span
5. TCS (temperature coefficient of Span)
6. Temperature hysteresis
7. Pressure hysteresis

Please refer to attached document.

As we can see, there are many variables which affect the end performance of the sensor and are included within the overall accuracy or uncertainty. The main error contributor in such systems are the temperature, and the offset. It may not possible to take any influence at the temperature in such systems. So, we have mainly to deal with the offset and the easiest and most efficient way to annul it is Auto-Zero.

Please refer to the following application note:

AN1636 - Implementing AutoZero for Integrated Pressure Sensor

In case you are interested about another solution, I would recommend the MPL3115A2 - I2C Precision Altimeter.

The MPL3115A2 has a wide operating range of 20 kPa to 110 kPa, a range that covers all surface elevations on earth.

Please find more information about the MPL3115A2 here.

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