The Pressures of Daily Life on Earth

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 pressures at sea level.

The Pressures of Daily Life on Earth

To get away from the usual routine and day to day stress, it’s great to take a summer vacation. Many people, even those in the center of the country, like to go on a seaside vacation near an ocean. For those concerned about pressure, at sea level the barometric pressure is 1 atmosphere (14.7 psi, 101 kPa, 29.9 in. Hg, or 760 mm Hg).

Surprisingly, the pressure at sea level is higher than most places on earth. At the top of Mt. Everest (altitude 29,029 feet or 8,848 m), the highest elevation in the world, the summit pressure of 251–253 Torr (33.5 to 33.7 kPa or 4.84 to 4.89 psi) is about 1/3rd of sea level based on measurements made from May to October. (For altitude pressure calculations, click here.) While the pressure is considerably less than sea level or anywhere else on earth, in spite of the exhilaration of being on top of the world, the stress level has to be incredibly high.

In contrast, the Mariana trench at the bottom of the ocean in the western Pacific Ocean is 35,814 feet (or 10.9 km) below sea level and the pressure is about 1.1 × 108 Pa (16,000 psi) or over  1000 atmospheres. That is serious pressure and only three human beings have made the trip. (For under water pressure calculations, click here.)

Compared to the extreme alternatives, a sea side vacation seems like a reasonable way to escape the pressures of daily life.

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 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)

Controlling Building Pressure

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 proper indoor versus outdoor pressure in commercial buildings.

Controlling Building Pressure

Proper indoor versus outdoor pressure is important in commercial buildings. When indoor pressure is less than the outside pressure, outdoor air leaks, or infiltrates into the building. In addition to impacting heating, ventilation and air conditioning (HVAC) effectiveness, excessive infiltration can also cause uncomfortable drafts, especially in stairways, as well possible odor migrations and even encourage microbial growth depending on the outside weather conditions.

The opposite pressure condition, exfiltration, occurs when indoor pressure is greater than the outside pressure, indoor air leaks out of, or exfiltrates from the building. Excessive exfiltration negatively impacts temperature control by reducing supply airflow into occupied spaces, makes opening and closing doors difficult and creates noisy high-velocity airflow around doors and windows.

In addition to the operation of its mechanical ventilation system, a building’s pressure can be positive or negative due to the impact of wind and weather. Using either a return fan or a relief fan, for direct control of building pressure, manages the combined effects of weather, wind, and mechanical ventilation. This control requires pressure sensors mounted inside and outside of the building to determine the actual pressure difference. Depending on the desired exfiltration and infiltration goals, the pressure difference is typically less than 0.1-inch water gauge (wg) and can be either positive or negative.

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)

Summertime and the Livin’ is Easy – with Pressure Sensors

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 sensors for pool filters.

Summertime and the Livin’ is Easy – with Pressure Sensors

Well, it’s officially summer and one of the “livin’ is easy” moments occurs when you get to spend some time in a pool. While the pool is refreshing, there is a maintenance side and work involved in keeping it clean. The pool filter maintenance indicator is a pressure sensor that typically has a 0-60 PSI gage readout.

The pressure sensor measures a gage reading, the pressure in the filter, since it does not have to record flow. A normal operating pressure is observed when the pool filter is clean and running at a specified rpm. When the pressure in the filter increases by a few psi, it’s time for backwashing.

Since the gauge requires an operator to determine if it is time for backwashing, the sensors are simple mechanical sensors. For other filter applications that require an electronic signal, a MEMS pressure sensor usually is preferred to other sensor technology options for cost, ease of interface and reliability reasons. This is the case for commercial air filters and healthcare applications such as high-efficiency particulate air (HEPA) ultra-low penetration air (ULPA) filtration systems or ventilation units.

HEPA and ULPA filters are typically operated under pressure of approximately 203 mm (8in.) of water column. For these types of applications flow is typically measured, so a differential rather than static pressure measurement is made to determine when it is time to replace the filter. While measuring air simplifies the mechanical interface and avoids problems with liquids, the small ∆P measurement requires a specially designed pressure range to produce an easily managed output. In any case, this is an application easily handled by MEMS pressure sensors.

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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)