Static Pressure measurements using a Paroscientific Digiquartz solid state transducer. Standard State Parameter on both aircraft platforms.
Full Name: Ambient Static Pressure
Short Name or Acronym: PSF, PSFD, PSFRD
Model if applicable: Paroscientific Digiquartz Series 1000
Measurements Provided: Absolute Pressure
Manufacturer or Builder of the Instrument: Paroscientific
When Acquired: 2005
Operational Status: Standard State Parameter on both aircraft
General Description: “Static pressure,” also called “ambient pressure,” is the pressure of the atmosphere at the flight level of the aircraft. It is called static pressure to distinguish it from dynamic pressure, which is the pressure present at a forward-pointing aperture on the aircraft and therefore includes the pressure generated by airflow. On research aircraft operated by NCAR, static pressure is measured using Paroscientific Digiquartz Series 1000 transduceers that sense the pressure at “static buttons,” special ports mounted on the sides of the fuselage in locations selected to deliver a pressure close to the ambient. Additional corrections, based on reference measurements such as those from a trailing cone, are applied to remove small remaining deviations between the pressure at the static buttons and the true ambient pressure. See the discussion in the tutorial in the “Documents” section at the end of this page. In that section, under Processing Algorithms, there is also a discussion of the current method of determining pressure corrections by reference to a Laser Air Motion Sensor (LAMS); see also the discussion of the LAMS elsewhere in this discussion of RAF Instruments.
Measurement Characteristics:
Overall system for ambient pressure measurement: Accuracy 0.3 mb, precision <0.1 mb, response time < 0.1 s
Calibration Methods: RAF Calibration Cart / Transfer Standard; Empirically Derived Corrections (Pcors) to adjust for location and airspeed effects. Calibrations are performed regularly and data processing incorporates the latest calibration for each project. In addition, tests to determine the accuracy of the “static button” pressure sources on the GV have been used to determine corrections that are dependent on angle of attack, pressure, and dynamic pressure. These corrections have been determined in three ways: (1) via tests using a trailing-cone pressure port; (2) via comparisons to the standard avionics pressure measurement on the aircraft (which has been demonstrated to meet Reduced Vertical Separation Minimum (RVSM) standards; and (3) measurements from a laser air motion sensing system, which is used to calibrate dynamic pressure and hence, under the assumption that static pressure is measured with high accuracy, total pressure. Overall accuracy is estimated at < 0.3 mb.
History of Significant Changes to the Instrument: none
Description of Software, Data Handling, and Data Flow: Standard nimbus processing.
Software Components (data acquisition, display, processing, and analysis):
Data Processing Chain (from flight to archival): Digital output from the sensor is recorded by the aircraft data system and the measurements are then included in standard netCDF data files produced by the RAF. The primary output variable is named "PSXC" and is the ambient pressure in units of hPa. The normal output frequency is 1 Hz; 25 Hz measurements can also be produced. For more information, see the StandardDataPath page.
QA Procedures and Needs: Comparison against avionics and redundant sensors
Safety Issues: none
Examples of Measurements:
Lead Contact: Allen Schanot
Operating Manual User Manual (pdf)
Memo documenting proposed changes to static pressure corrections based on LAMS
Presentation used for discussion of the changes to "PCORS" based on LAMS measurements
Internal users: See http://wiki.eol.ucar.edu/rafscience/StaticPressure (last edited 2012-12-09)