Tag Archives: altimeter

Pressure Sensing in Smartphones Provides Advanced Location Info and More

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll discuss pressure sensing in smartphones, buildings, and altimeters.

Pressure Sensing in Smartphones Provides Advanced Location Info and More

When Samsung wanted to go beyond its initial location technology that used accelerometer, gyroscope and magnetometer inputs, it added a pressure sensor to the Galaxy S4. With pressure, customers can obtain floor accurate indoor geolocation information. Not to be outdone, Apple included a pressure sensor in its iPhone 6. Today, many portable products have a pressure sensor.

Altimeters commonly use absolute pressure sensors and atmospheric pressure decreases as the altitude increases. The two are related by the equation:

h=(RT/gM)ln(p0/p)

where,

  • h is the difference between the starting height and the measurement height,
  • R is the universal gas constant (0.31447J/(mol • k)),
  • g is the gravitational constant at the earth surface (9.80665 m/s2 at the sea level),
  • M is the molar mass of air (0.0289644 kg/mol),
  • p0 is the atmospheric pressure at the starting height (e.g., 101, 325 Pa),
  • T is the temperature of air, and
  • p is the atmospheric pressure at the measurement height.

With 10 feet providing an average between residential and commercial floor heights, the ability to identify this distance allows the portable device to accurately predict the floor in multistory buildings.

In Samsung and other Android smartphones with a pressure sensor, the current elevation from the sea level is calculated from atmospheric pressure information of the current position and sea level pressure information by using the API provided in Android.

In fact, within a multistory building, accurate floor information is critical for blind or visually impaired individuals to find their way. This is among the more compelling uses of pressure sensor location technology and has lead researchers to develop more accurate means of calculating height than the previous equation, since many parameters are affected by weather.

Changes in atmospheric pressure, at a given altitude, are specifically used to predict weather changes. The combined input from millions of smartphones could be used in the future to more accurately model and predict weather patterns. Users can already download a free app called Weather Signal to report their iPhone pressure to a national data base. In smartphones, pressure sensors provide a new perspective to “what will they think of next?”

What do you think/Comments?
Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.
-Dan DeFalco, Marketing Manager, All Sensors Corporation (ddefalco@allsensors.com)