Manometer

A manometer is a scientific device that is used to pressure differences, this could be pressure relative to atmospheric pressure (a barometer), within a vessel or chamber, a gas or liquid to calculate flow rates through a device such as a duct or blood pressure in a person.

They are commonly used in the construction industry for building services to measure system air pressure in heating, ventilation, and air conditioning systems, airflows, positive and negative pressures in ducts, or pressure differentials across filters and coils. There are effectively four types of manometers, the first two relying on a fluid, in a closed or open tube, and the third, aneroid manometer, without a fluid and finally a digital aneroid manometer, they all measure pressure through comparison or differentials.

A barometer is a common closed tube type of manometer, the closed tube contains mercury, and it is used to measure in comparison to atmospheric pressure. These are familiar devices often found outside windows in homes, to measure the outside air pressure to assist in weather predictions, rising air pressure indicates a good weather forecast whilst falling pressure might forecast rain or bad weather. Another common type of manometer is a sphygmomanometer used to measure and monitor blood pressure, these are either mercury and aneroid types. Manometers are also a component part of balometers, airflow meters or air flow hoods, used to measure the flow rate of air leaving or entering the ventilation outlet of an airflow system.

There are a number of different open tube analogue types of manometers, which include U-tube, enlarged-leg, well-type and inclined-tube manometer each with a specific design varying approach and accuracy. They all essentially measure pressure exerted by the atmosphere at one end of the tube or one part of the design and compare this with a known pressure at the other or other part, to give the pressure. Aneroid manometers indicate by air pressure via an inflation device (such as a diaphragm or Bourdon tube).

The final type of manometer is a modern digital device, it does not use a fluid, but a pressure transducer. An elastic portion of the transducer detects pressure levels and converts this energy into an electronic signal, producing a number instantaneously on a digital display. Manometers essentially measure pressure difference by applying the fluid column principle in analogue devices and transducers in digital devices, this differs from pressure gauges which more specifically measure or check a single pressure, rather than by comparison.

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