A pressure gauge is an industrial instrument for measuring fluid pressure, primarily using elastic sensing elements—such as Bourdon tubes, diaphragm capsules, or bellows—that deform under pressure and, via a mechanical linkage, drive a pointer to indicate the pressure value. Key components include a pressure relief port (to vent overpressure and protect the device), a pointer, a glass lens (available in tempered or anti-reflective variants), and a protective case. Available in general-purpose, vibration-resistant, high-temperature, and explosion-proof types—with IP ratings indicating dust/water resistance—it covers a wide range from –0.1 MPa to 700 MPa, with specialized diaphragm capsule models capable of detecting micro-pressures as low as 2.5 kPa. Connections are made via brazing or TIG welding to suit various materials, and optional oil-free or water-free treatments enable compatibility with special media; some models also feature electrical contacts for pressure control or alarm functions.