Gauge pressure transmitters measure upwards of ambient atmospheric conditions, which average around one bar (100 kPa) at sea level. The measurements acquired by an absolute pressure transmitter are subsequently equal to gauge plus atmospheric pressure.
Many process conditions and materials are unaffected by variations in atmospheric pressure. Gauge pressure transmitters are typically used in such applications to provide a clear zero reference. This technology is often used in conjunction with thermal monitors and advanced gas sensors to monitor process conditions in petrochemical facilities, alongside the operating conditions of hydraulic and pneumatic components.
However, gauge pressure transmitters are unsuitable for measuring pressures that are affected by changes in atmospheric conditions. They may also be limited for process monitoring of closed systems where measured media is subject to density changes.
Applications of absolute pressure transmitters
The most common measure of barometric pressure is mean sea-level pressure (MSLP), which is measured from a vertical geodetic point accepted as the average sea level. The average MSLP is roughly 101.3 kPa. Absolute pressure transmitters are used in applications where gauge pressure transmitters are unsuitable, as gauge transmitters are incapable of measuring atmospheric conditions and would consistently display a zero reading if calibrated correctly.
There are a plethora of industrial processing applications that require absolute pressure of process gases and liquids to be maintained. Hydrogen (H2), for example, occupies different phase states dependent upon its temperature and pressure. Liquid H2 cannot exist at ambient temperatures or atmospheric pressures. It must be cooled beneath its critical point and contained in a hermetically-sealed pressure vessel to ensure it will not rapidly boil and convert back into a gas. Absolute pressure transmitters are typically used in gas sensing arrays for liquid gas processing, containment, and transport applications.
Among the most innovative uses of absolute pressure transmitters is process control and monitoring of ultra-high vacuum (UHV) manufacturing environments. Chemical vapour deposition (CVD) and various other gas phase technologies require vacuum conditions to be maintained while gaseous precursors are deposited onto catalytic substrates. This methodology is broadly used to manufacture thin-film structures for electronics applications, including organic photovoltaics (OPVs) and digital displays.
Absolute pressure transmitters from ABB
ABB offers an extensive selection of absolute pressure transmitters with unique measurement technologies for distinct operating conditions. These include remote diaphragm sealing, wireless communications, overload protection, and compact pressure transmitter head architectures.
If you would like any more information about our absolute pressure transmitters, please find your local contact below.