Development of the national pressure standard for the Spanish Metrology Centre (CEM)
To have a national pressure standard.
Development of the national pressure standard so the CEM is able to measure absolute pressures up to 3 bar with an uncertainty level below + 0.5 Pa.
The development has consisted of the use of a double liquid mercury column.
Its operation is based on the primitive experiment of Torricelli. With a perfect liquid introduced into a U-shaped tube, when the pressures at each end differ in a (DP) value, between them there is a difference in height, h, meaning that DP=r·g·h, where r is the liquid mass density, g is the acceleration of local gravity, and h is the difference in heights.
When a vacuum is performed at one of the ends, the measured DP is the absolute pressure measurement.
This simple principle is full of challenges due to the low level of uncertainty required for the device to be the national pressure standard. The measurement of the mercury column heights with laser interferometry and compensation tracker, the pureness of the mercury (99.99999%), the temperature control with uniformity below 0.01 ºK, the total vibratory isolation through the special foundations, have been some of the challenges we have overcome in this project until achieving the most precise "barometer" in the world.