Pressure Measurement

What is a barometer and what is it used for?

A barometer is a pressure sensor that is used to measure atmospheric pressure. This device is very sensitive, and they are capable to measure the absolute pressure. A barometer can measure the pressure exerted by the atmosphere with the help of water, air, or mercury. The atmospheric pressure would change according to the distance above or below the sea level, the barometer can also be used to measure altitude. The major types of barometers that are widely used are mercury and aneroid barometer. The barometer can measure the atmospheric pressure in units of measurement called atmospheres or bars.

  • A mercury barometer consists of a glass tube, and this glass tube is closed at one end and it has an open mercury-filled reservoir at the base.
  • The vacuum will be created on the top of the tube because of the weight of the mercury, so if the mercury level falls in the glass tube then the vacuum is created in the top.
  • So basically a mercury barometer operates by balancing the mercury weight in the glass tube over the weight of the atmospheric pressure.
  • The mercury level in the glass tube increases if the weight of the mercury is less than the atmospheric pressure.
  • The mercury level would decrease if the weight of the mercury is greater than the atmospheric pressure.
  • The mercury level would change constantly till the weight of the mercury in the tube is equal to the weight of air above the reservoir. By using a ruler we can measure the rising and falling of mercury.  
What is a barometer and what is it used for? 1
  • The aneroid barometer can be considered an advanced barometer because it doesn’t have the disadvantages of a mercury barometer.
  • The mercury barometer is fragile and it won’t work properly if it is disturbed by outside motion. The aneroid barometer doesn’t use any liquid and it is really compact.
  • The portability of the aneroid barometer makes it a suitable device to use at sea or in the field.
  • An aneroid barometer has a sealed chamber and it would expand and contract according to the atmospheric pressure around it.
  • By using certain mechanical tools we can measure how much the chamber expands and contracts. The aneroid barometer consists of a flexible walled evacuated capsule, this wall would deflect according to the changes in atmospheric pressure.
  • Digital barometers have revolutionized atmospheric measurement by providing more accurate and rapid data than ever before.
  • They not only display current barometric readings but also show previous readings from the last one, three, six, and twelve hours in a bar chart format, similar to a barograph.
  • Additionally, these devices incorporate other atmospheric data, such as wind and humidity, to enhance weather forecasting accuracy.
  • The collected data is stored on the device and can be downloaded to a computer for further analysis. Meteorologists and scientists rely on digital barometers for real-time atmospheric readings during experiments, whether in the lab or the field.
  • Digital barometers have also become a vital tool in modern smartphones, where they use atmospheric pressure data to provide accurate elevation readings, significantly improving GPS navigation.
  • Developers and researchers leverage the crowdsourcing capabilities of smartphones to enhance weather forecasting accuracy.
  • Apps like PressureNet automatically gather barometric measurements from users, creating a vast network of atmospheric data. This network facilitates quicker and more precise storm mapping, especially in regions with limited weather stations.
  • This type of barometer has a glass container with a sealed body and it will be half-filled with water.
  • A narrow spout connects to the body below the water level and rises above the water level and the narrow spout is open to the atmosphere.
  • So when the air pressure is lower than it was at the time the body was sealed, the water level in the spout will rise above the water level in the body.
  • When the air pressure is high then the water level in the spout will drop below the water level in the body.
  • A barograph is a type of recording aneroid barometer that continuously records changes in atmospheric pressure on a paper chart.
  • Similar to an aneroid barometer, a barograph uses small movements within the barometric box. These movements are transmitted through a system of levers to a recording arm equipped with either a scribe or a pen.
  • The scribe marks on smoked foil, while the pen writes on paper with ink. The recording material is mounted on a cylindrical drum that rotates slowly, often once per day, week, or month, depending on user preference.

When atmospheric pressure is measured using a barometer, it’s referred to as “barometric pressure.” Consider a barometer with a cross-sectional area A and a height hhh, filled with mercury from the bottom at Point B to the top at Point C. The pressure at Point B is equal to the atmospheric pressure, while the pressure at Point C can be considered zero because there’s only mercury vapor above this point, and its pressure is negligible relative to atmospheric pressure. The atmospheric pressure can be determined using the barometer and the following equation:

Patm=ρgh

Where:

  • Patm​ is the atmospheric pressure,
  • ρ is the density of mercury,
  • g is the gravitational acceleration, and
  • h is the height of the mercury column above the free surface.

The physical dimensions of the barometer, such as the length and cross-sectional area of the tube, do not affect the height of the fluid column.

In thermodynamic calculations, a standard unit of pressure often used is the “standard atmosphere,” which corresponds to the pressure exerted by a column of mercury 760 mm in height at 0°C.

For calculations,

The density of mercury is ρHg=13,595 kg/m3

gravitational acceleration is g=9.807 m/s2

If water were used instead of mercury, a water column of approximately 10.3 m (33.8 ft) would be required to meet standard atmospheric pressure.

Patm (kPa)Altitude (m)Patm (inHg)Altitude (ft)
101.3250 (Sea Level)29.920 (Sea Level)
97.7130528.861,000
94.2161027.822,000
89.881,00026.553,281
84.311,52424.905,000
79.502,00023.486,562
69.683,04820.5810,000
54.055,00015.9616,404
46.566,09613.7520,000
37.657,62011.1225,000
32.778,848*9.6829,029*
26.4410,0007.8132,808
11.6515,2403.4450,000
5.5320,0001.6365,617

*Note: The elevation of Mount Everest, the highest point on Earth.
*1 torr = 133.3 Pa = 0.03937 inHg.

A barometer measures atmospheric pressure using different methods, depending on its type. Here’s a common overview of how barometers operate:

A glass tube is filled with mercury and inverted into a mercury reservoir. Atmospheric pressure on the surface of the mercury in the reservoir supports the mercury column in the tube.

The height of the mercury column indicates atmospheric pressure. Higher columns mean higher pressure, while lower columns indicate lower pressure.

Contains a sealed metal chamber (aneroid cell) that flexes with changes in atmospheric pressure.

The flexing movements of the chamber are transmitted to a needle on a dial, displaying the atmospheric pressure.

Uses electronic sensors to measure atmospheric pressure.

Converts pressure readings into digital signals displayed on a screen. These devices can also store data and provide additional information like altitude.

A glass container is partially filled with water, with a narrow spout open to the atmosphere.

Changes in atmospheric pressure cause the water level in the spout to rise or fall relative to the container. Lower pressure raises the water level, while higher pressure lowers it.

  • Before reading the barometer it must be slightly tapped, while checking the needle we must gently tap the glass and must check which way the needle moves.
  • We can determine the increase and decrease in pressure by using a barometer and if the needle isn’t moving then the barometer is holding steady
  • The barometer is a device that can measure air pressure the rising barometer indicates the rising air pressure and the falling barometer shows the decrease in air pressure.  
  • It is used to measure weather
  • Science and industry
  • It is used in watches and smartphones
  • This device can be used to check the altitude
  • Aneroid barometers are used in portable instruments
  • The aneroid barometer is used in aircraft altimeters
  • A barometer is an instrument used to measure atmospheric pressure, which is its most common application, particularly for monitoring weather changes.
  • This measurement is crucial for weather forecasting and understanding storm patterns.
  • Barometers function similarly to a set of scales, with mercury barometers balancing a column of mercury against atmospheric pressure for precise measurement.
  • There are two main types of barometers: mercury barometers, which use liquid mercury, and aneroid barometers, which are non-liquid.
  • Additionally, barometers can also be used to measure altitude, as atmospheric pressure varies with elevation.

A barometer, which measures atmospheric pressure, can be used in various settings. It is most commonly used in weather forecasting to monitor pressure changes and predict weather patterns. Barometers are also used to determine altitude, as atmospheric pressure varies with elevation, whether you are going further above, closer to, or below sea level.

A barometer is used in the field of meteorology to measure atmospheric pressure and predict changes in the weather. It is also used to measure altitude in certain situations. Scientists today read barometric pressure measurements in units such as pascals and kilopascals.

A barograph is a device used to measure and record changing air pressure on a chart using a continuous pen and ink trace. The chart produced by a barograph is known as a barogram. In addition to barographs, other types of barometers can also record pressure data on paper forms. Atmospheric pressure is typically measured in millibars or inches of mercury.

Meteorologists primarily use barometers to predict short-term weather changes. A rapid drop in atmospheric pressure indicates the arrival of a low-pressure system, which often leads to cloudy, rainy, or windy conditions. Barometers help meteorologists understand how air moves, particularly how it shifts away from areas of high pressure.

  1. Measurement of Atmospheric Pressure: Barometers are primarily used to measure the atmospheric pressure at a specific location.
  2. Determining Altitude: Barometers can help determine the altitude of a place, as atmospheric pressure decreases with increasing elevation.
  3. Weather Forecasting: Barometers are essential tools in predicting weather changes by monitoring fluctuations in atmospheric pressure.
  4. Calibration and Checking of Aneroid Barometers: Mercury barometers are often used to calibrate and check the accuracy of aneroid barometers.
  5. Application in Fluid Mechanics: Barometers are utilized in fluid mechanics to study and analyze fluid behavior under different pressure conditions.
  6. Measurement of Pressure in Aircraft: In aviation, barometers measure the atmospheric pressure to assist in altitude determination and ensure safe flight operations.
  7. Surface Weather Analysis: Barometers are used in meteorology for surface weather analysis, helping to map pressure systems like high and low-pressure areas.
  8. Preparation of Barographs: Barometers are employed in the preparation of barographs, which record continuous atmospheric pressure changes over time.
  9. Navigation Assistance: Barometers are used in marine and aeronautical navigation to help determine altitude and forecast weather conditions.
  10. Scientific Research: Barometers are used in scientific research to monitor and analyze atmospheric conditions in various environmental studies.

Click here for In-Depth Guide to Pressure Measuring Instruments and Calibration

Ashlin

post-graduate in Electronics & communication.

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