Manometer Definition and Purpose

A manometer is a scientific instrument used to measure gas pressures. Open manometers measure gas pressure relative to atmospheric pressure. A mercury or oil manometer measures gas pressure as the height of a fluid column of mercury or oil that the gas sample supports.

How this works is, a column of mercury (or oil) is open at one end to the atmosphere and exposed to the pressure to be measured at the other end. Before use, the column is calibrated so that markings to indicate height correspond to known pressures. If atmospheric pressure is greater than the pressure on the other side of the fluid, air pressure pushes the column toward the other vapor. If the opposing vapor pressure is greater than atmospheric pressure, the column is pushed toward the side open to air.

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Barometer Definition and Function

By Anne Marie Helmenstine, Ph.D.

Common Misspellings: mannometer, manameter

Example of a Manometer

Probably the most familiar example of a manometer is a sphygmomanometer, which is used to measure blood pressure. The device consists of an inflatable cuff that collapses and releases the artery beneath it. A mercury or mechanical (anaeroid) manometer is attached to the cuff to measure a change in pressure. While aneroid sphygmomanometers are considered safer because they don't utilize toxic mercury and are less expensive, they are less accurate and require frequent calibration checks. Mercury sphygmomanometers display changes in blood pressure by changing the height of a mercury column. A stethoscope is used with the manometer for auscultation.

Other Devices for Pressure Measurement

In addition to the manometer, there are other techniques to measure pressure and vacuum. These include the McLeod gauge, the Bourdon gauge, and electronic pressure sensors.