Barometers are instruments that determine absolute pressure. Absolute pressure is defined as the compression force exerted by the weight of air molecules in the surrounding atmosphere. Absolute pressure readings are always corrected with the sea level (altitude), as altitude changes affect the air density. Absolute pressure decreases with the increasing altitude due to the lower air density, and increases when closer to earth. Accounting for these altitude corrections, modern Barometers have altimeters integrated, to avoid revisions in the absolute pressure reading.
Similar to Absolute pressure, Gauge and Differential pressures are also considered standard pressure units. Gauge pressure is the default parameter across industries and is defined as the difference between Absolute and Atmospheric pressures. Gauge pressure is referred to while monitoring the tire pressure, blood pressure, pump capacity, or specifications of any industrial equipment. Differential pressure , on the other hand, is the gauge pressure difference measured between two points. Differential pressure gauges consist of two inlet ports, each connected to two different volumes. The movement of fluid in the mercury column of the barometer indicates high and low-pressure zones.
Hydrostatic-based barometers use hydrostatic fluids (commonly water and mercury) to determine atmospheric pressure. These barometers consist of a transparent columnar tube, usually made of solid glass and filled with a static, in-compressible liquid. The columnar section is sealed one end to hold the vacuum and partially filled with the incompressible liquid. The other end is open to the atmosphere and makes an interface with the surrounding environment. As the atmospheric pressure changes, the pressure exerted by the atmosphere on the liquid reservoir exposed to the atmosphere changes and causes the liquid to move. Gradations are marked on the tube to record the fluid level (above the base-point), converted as Absolute pressure using the formula “ρgh,” where ρ, g, and h represent the density, acceleration due to gravity, and the level of mercury (above the base-point) respectively. While water as an incompressible liquid is less hazardous than mercury, mercury is often a better choice for fabricating accurate hydrostatic barometers due to its higher density, yielding better accuracy.
Aneroid or Electronic barometers consist of a tiny, flexible sealed metal box called an aneroid cell made from beryllium-copper alloy. Changes in external air pressure cause the aneroid cell to expand or contract. Mechanical mechanisms amplify this expansion and contraction to give a pressure reading. Modern pressure measuring devices are designed to convert the absolute pressure to provide gauge pressure readings. Aneroid barometers are more practical than hydrostatic barometers because of their robustness and accuracy. While the aneroid barometer is the underlying mechanism behind modern absolute pressure measuring devices, pressure can also be measured using simpler and sophisticated methods.
Barometers are selected based on the application, level of accuracy, and electrical integration requirements. Following are the barometer categories, grouped with their features:
Certain corrections are applied to ensure that the observed barometer reading is rendered accurate. Correction factors account for instrument errors and atmospheric corrections and are broadly classified as:
Following errors set in within a Barometer due to prolonged usage at various operating conditions. Operators should measure and eliminated these errors using calibration and resetting:
Cumulative defects in a barometer often result in operational uncertainties leading to maintenance loss. Calibration avoids these errors, ensures timers’ accuracy for sustained and repeated use, and enhances service life. Following a regular and timely calibration schedule ensures accuracy of measurement and enhances process accuracy.
e2b calibration offers industry-leading ISO-certified Barometer calibration services. Our labs are ISO/IEC 17025 accredited and operated by a team of qualified calibration experts to test and calibrate your barometers. Our verifiable services are unmatched in the industry. We are registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. Contact e2b calibration for all your equipment calibration needs.