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Under Pressure

October 19, 2020

There’s a Keystone in every great invention.

Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. The Atlantic Ocean hurricane season runs from June through November every year. In the Atlantic Ocean, storms are categorized as hurricanes, tropical storms, or tropical depressions. The ongoing 2020 hurricane season has already been a record-breaking year in terms of the number of named storms. On average, the Atlantic hurricane season experiences 10.1 named storms occur each season, with an average of 5.9 becoming hurricanes and 2.5 becoming major hurricanes. In 2020, we have already seen a total of 27 tropical or subtropical cyclones, 26 named storms, 10 hurricanes, and 4 major hurricanes.

The development of barometers has been instrumental in tracking changes in air pressure for early storm detection. Early detection means more time for the general public to prepare for storms, and potential evacuation before the tropical storm hits land.

Barometer Overview

Atmospheric (air) pressure is the pressure within the atmosphere. A barometer is a scientific instrument used to measure the amount of pressure exerted by the weight of the atmosphere in a certain environment. Named after the instrument, atmospheric pressure is also often referred to as barometric pressure. Air pressure is measured in pascals or pounds per square inch. At sea level, the mean air pressure value is 101,325 pascals, or roughly 14.6959 pounds per square inch.

Pressure norms and fluctuations can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries. High pressure systems usually indicate clear, sunny weather while low pressure systems typically bring clouds and rain. So, a barometer with a high pressure reading is forecasting sunny weather, while a barometer reading showing falling pressure means that a low pressure system is moving in, and you can expect poorer weather.

History of Barometers

It was once thought that the air above us did not hold any weight, and thus did not exert any force on the bodies below. Evangelista Torricelli challenged this thought, and is credited with inventing the mercury barometer in 1643 to prove his theory. Documentation also suggests an Italian mathematician and astronomer named Gasparo Berti unintentionally built a water barometer sometime between 1640 and 1643. French scientist and philosopher René Descartes described an experiment to determine atmospheric pressure as early as 1631, but there is no documentation that he built a working barometer.

In September 1646, Blaise Pascal expanded on Torricelli's theories and developed an experiment with his brother-in-law, Florin Perier. Using a mercury barometer, Florin Perier took atmospheric measurements as he climbed mount Puy de Dome. When comparing the barometric readings on the mountain to those from the foot of the mountain, Pascal confirmed that the mercury barometer readings were lower the higher one went. Pascal and Perier had proven air has weight and it is lighter the higher one travels.

Since Torricelli and Pascal, many other types of barometers have been developed. Here is a brief description of barometers and how they function:

  • Water-based Barometer: consists of a glass container with a sealed body, half filled with water. A narrow spout connects to the body below the water level and rises above the water level. The narrow spout is open to the atmosphere. 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 higher, the water level in the spout will drop below the water level in the body. 
  • Mercury Barometer: Also =known as the Torricell barometer, the instrument features a sealed, vertical glass tube with a mercury-filled basin at the bottom. High atmospheric pressure places more force on the reservoir, moving the mercury higher in the glass tube. Low pressure has a lower force, which allows more mercury to drop back into the reservoir, displaying a lower reading on the glass column.
  • Fortin Barometer: Uses a variable displacement mercury cistern that compensates for displacement of mercury in a column with varying pressure. The level of mercury is set to zero by using the thumbscrew to make an ivory pointer just touch the surface of the mercury. The pressure is then read on the column by adjusting a vernier scale so that the mercury just touches a sightline.
  • Wheel Barometer: around 1810, the wheel barometer became the first practical and commercial instrument favored by farmers and the educated classes in the UK. The circular instrument could be read at great distances with its simple scale: "Rain - Change - Dry" with the "Change" at the top center of the dial. As atmospheric pressure increases, mercury moves in a sealed tube causing a float to fall and direct the pointer. When pressure increases the mercury moves back, lifting the float and turning the dial the other way.
  • Vacuum Pumped Oil Barometer: Uses doubly distilled vacuum pump oil as the working fluid, which enabled the creation of the "World's Tallest Barometer" in February 2013. Located at Portland State University, the barometer has a nominal height of about 12.4 m for the oil column height.
  • Aneroid Barometer: Invented in 1844 by French scientist Lucien Vidi, the aneroid barometer does not use liquid. Instead, a small, flexible metal capsule made from an alloy of beryllium and copper is evacuated. When the air pressure rises, the sides of the capsule are compressed. The capsule is attached to levers which move a needle as the air pressure squeezes the capsule. A dial behind the needle tells you the air pressure and altitude or weather forecast.
  • Barograph Barometer: a recording aneroid barometer where the changes in atmospheric pressure are recorded on a paper chart.
  • MEMS Barometer: Extremely small devices typically ranging between 1 and 100 micrometers in size (0.001 to 0.1 mm), microelectromechanical systems (MEMS) barometers are created with photolithography or photochemical machining. Typical applications include miniaturized weather stations, electronic barometers and altimeters.

Modern Barometers

Modern barometers are digital and show the pressure reading on an LCD display. Digital barometers offer extremely accurate readings in seconds. Barometer applications have expanded beyond weather forecasting. Modern electronic barometric pressure sensors are used automotive, portable device, manufacturing and clean-room applications. Many modern barometers offer temperature and humidity readings in addition to atmospheric pressure.

A wide range of Keystone products can be found in modern barometric systems. Keystone products give electronic barometric systems a longer, more reliable operating life. Keystone products, including LED holders, spacers and lens caps; fuse clips and holdersPCB test points and terminals; spacers and standoffs; panel hardware and PCB plugs, pins, jacks, and sockets are commonly used in electronic barometric systems.