Tag Archives: atmospheric pressure

Out of this World Pressures

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 be discussing pressure outside of our blue planet.

Out of this World Pressures

The earth’s average atmospheric pressure is 1 bar (101.3kPa, 29.92 mm Hg or 14.69 psi). Temperature and altitude are among the factors that cause variations. At a specific location, the air pressure can vary about 10%. Leave this planet, where we have the weight of a life-producing atmosphere of oxygen and nitrogen exerting pressure on us and the situation is quite different.

In outer space, the pressure is 1.322 × 10-11 Pa – essentially zero, since there is very little air and hardly any water.

Our nearest neighbor, the moon, has a surface pressure at night of 3 x 10-15 bar (or 3 x10-10 Pa). In contrast, Mars has a layer of gases surrounding it composed mostly of carbon dioxide. As a result, the atmospheric pressure on the Martian surface averages average  750 Pa (0.109 psi) or about 1/100 of the Earth’s. At any given location on Mars, the air pressure can vary by as much as 50%.

Earth’s pressure variations at a given location seem small compared to these other locations. Measuring earth’s pressure variations is also quite easy and commonly performed with a 100 kPa absolute pressure sensor.

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The size difference between Earth and Mars is minor compared to the atmospheric pressure difference. Image courtesy of NASA.

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

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)

Pressure’s Role in Predicting Weather

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 look at how pressure helps predict weather.

Pressure’s Role in Predicting Weather

With all the harsh winter weather occurring recently, knowing what to expect in your area is important knowledge for short term planning and, in some areas such as the northeast, for long term planning. Sensing barometric pressure was one of the earliest forecasting tools and continues to be important today.

One website provides the barometric pressure history from numerous major cities in the U.S. from Friday, Feb 20 to Thursday, Feb 26. The high and low readings only tell part of the story. The intensity of the weather depends on how quickly the front develops and other factors.

City Highest pressure in period (In. Hg) Lowest pressure in period (In. Hg)
Boston 30.55 29.55
Minneapolis 30.8 29.65
Denver 30.35 29.75
San Francisco 30.35 29.85
Chicago 30.7 29.7

In stormy weather, the barometric pressure tends to be lower and a lower reading is one sign of approaching inclement weather.  During fair weather, the barometric pressure is typically higher and if the pressure begins to rise, it is a sign of tranquil weather.

According to the webpage CHANGES IN ATMOSPHERIC PRESSURE, the barometric pressure is reduced through several processes:

  • The approach of a low pressure trough
  • The deepening of a low pressure trough
  • A reduction of mass caused by upper level divergence (vorticity, jet streaks)
  • Moisture advection (moist air is less dense than dry air)
  • Warm air advection (warm air is less dense than cold air)
  • Rising air (such as near a frontal boundary or any process that causes rising air)

In the U.S., the Federal government uses pressure as part of several methods available to predict weather. On Feb26, the weather in many places around the U.S. was much less severe than it had been in recent weeks with at least one exception.

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THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH AND CENTRAL NEW MEXICO.

  • Humidity 63%
  • Wind Speed SE 20 mph
  • Barometer 30.04 in. Hg. (1017.6 mb)
  • Dew point 17°F (-8°C)
  • Visibility 9.00 mi
  • Wind Chill 15°F (-9°C)

For weather forecasting and other sensing applications, accuracy and other factors make the measurement acceptable for reliable use. That is where the expertise of the user comes into play.

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)