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Freescale Semiconductor Document Number: AN4528
Application Note Rev. 0, 07/2012
© 2012 Freescale Semiconductor, Inc. All rights reserved.
Contents
Pressure Altimetry using the
MPL3115A2
by: George Guo
1 Introduction
An altimeter is an instrument used to measure the
altitude of an object above a fixed level. One of the most
common types of altimeters is a pressure altimeter. A
pressure altimeter measures atmospheric-pressure data
to determine the altitude. They are widely used in
aviation, and in association with topographical and
geographical activities. With the development of
pressure-sensor technology, pressure altimeters are
becoming more affordable, sophisticated and used in our
daily life for activities such as hiking, climbing,
outdoor/indoor localization for GPS assist, E911 or
location-based services.
Freescale's Xtrinsic MPL3115A2 is a precision altimeter
and employs a MEMS pressure sensor with an I
2
C
interface to provide accurate pressure or altitude data. It
has very low-power consumption, smart features and
requires no data processing for mobile devices, medical
and security applications.
This application note answers some frequently asked
questions in pressure-altimeter applications with the
altitude under 11 km above sea level (the range of the
MPL3115A2). This document also shows how to use the
device’s smart features to develop feasible and effective
product solutions.
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Related Documentation. . . . . . . . . . . . . . . . . . . . . . 2
2 Basic Knowledge and Terminology. . . . . . . . . . . . . . . . . 2
3 Altitude Atmospheric-Pressure Variation . . . . . . . . . . . . 3
4 Working Principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5 Measurement Range. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6 Measurement Accuracy. . . . . . . . . . . . . . . . . . . . . . . . . . 8
7 Effect in Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
