Measurements of pressure relative to atmospheric reference pressure are enabled by a sealed enclosure, which in one aspect is a variable volume enclosure including a movable element responsive to atmospheric pressure, to at least partially equalize pressure internal to the variable volume enclosure to the pressure external to the variable volume enclosure, such that a pressure sensor pneumatically connected to the internal volume can use its pressure a reference in measuring atmospheric pressure. The variable volume enclosure may house electronics and/or electrical terminations for pressure sensing, or the variable volume enclosure may be a sub-enclosure connected pneumatically to the pressure sensor, with another enclosure housing electronics or electrical terminations. In another embodiment, the sealed enclosure includes an absolute pressure sensor for sensing atmospheric pressure for use as a reference, and need not have variable volume.

Measurements of pressure relative to atmospheric reference pressure are enabled by a sealed enclosure, which in one aspect is a variable volume enclosure including a movable element responsive to atmospheric pressure, to at least partially equalize pressure internal to the variable volume enclosure to the pressure external to the variable volume enclosure, such that a pressure sensor pneumatically connected to the internal volume can use its pressure a reference in measuring atmospheric pressure. The variable volume enclosure may house electronics and/or electrical terminations for pressure sensing, or the variable volume enclosure may be a sub-enclosure connected pneumatically to the pressure sensor, with another enclosure housing electronics or electrical terminations. In another embodiment, the sealed enclosure includes an absolute pressure sensor for sensing atmospheric pressure for use as a reference, and need not have variable volume.

A detector that detects an alarm and/or fault condition with respect to a pressure of a medium is provided. The detector comprises a housing comprising an access tube configured to receive a medium and a bellows fixed to the housing comprising a cavity and a first contact surface. The detector also comprises an adjustment screw positioned within the cavity of the bellows, coupled to the housing via an insulation member, and comprising a second contact surface. The detector is further configured to detect a change in pressure of the medium based on whether the first contact surface and the first contact surface are in electrical communication.

A detector that detects an alarm and/or fault condition with respect to a pressure of a medium is provided. The detector comprises a housing comprising an access tube configured to receive a medium and a bellows fixed to the housing comprising a cavity and a first contact surface. The detector also comprises an adjustment screw positioned within the cavity of the bellows, coupled to the housing via an insulation member, and comprising a second contact surface. The detector is further configured to detect a change in pressure of the medium based on whether the first contact surface and the first contact surface are in electrical communication.

A pressure sensor including a transducer housing, a transducer crystal disposed in the housing in vacuum conditions, a driver in contact with the crystal transducer, and a deflectable member in contact with the driver on one surface and exposed to ambient pressure on the opposite surface thereof. A borehole system including a borehole in a subsurface formation, a string in the borehole, and a sensor connected to the string.