What apparatus is used to provide the NPL online barograph? (FAQ - Pressure)
The instrument currently used to measure atmospheric pressure for the NPL online barograph is a good quality, commercially available resonant pressure sensor. Two such instruments are periodically calibrated against the UK's National Standard Barometer at NPL and the corrections determined during that process are then applied automatically, to each subsequent measurement, by NPL-written software running on a PC. The sensors are permanently connected to the PC which is permanently connected to the Internet server. The second instrument is used to ensure continuity of web data availability whilst the first one is being calibrated; at any time only one is in service.
The performance of all instrumentation changes with time and indeed the sensors used in the NPL online barograph, despite being state-of-the-art devices, have changed significantly since being installed and continuity of performance and accuracy is only achieved by regularly recalibrating the sensors and updating the calibration correction data applied by the host computer.