Development of an oil-based interferometric micromanometer as a primary absolute and gauge pressure standard (PTB)
Keywords: primary standard – liquid column manometer – in-situ density measurement – interferometric length measurement – vacuum oil analysis – ab-/desorption kinetics
The aim of this work package is to design, assemble and evaluate an oil-based interferometric micromanometer as a primary standard of absolute and gauge pressure in the pressure range up to 2 kPa. This instrument will provide a primary realisation of the pressure unit in the intermediate pressure range and close the gap between the pressure and vacuum areas which are covered by such primary pressure standards. This includes dead-weight pressure balances and mercury manometers (pressure) and static and continuous expansion systems (vacuum). In order to meet industrial demands and allow calibrations of commercial high-accuracy secondary pressure standards such as force-compensated digital piston gauges of FPG and FRS type, the desired measurement uncertainty should be as low as 1 mPa + 2·10-5p.
The tasks of this work packages are:
Task 1.1. An oil-based U-tube micromanometer, the interferometric system for oil surface detection and measurement of the oil column heights as well as design of floats with a capability to provide stable, disturbance-free oil surfaces in their cavities will be designed and developed.
Task 1.2. Analysis and choice of oils suitable as a manometric fluid; focusing on such mechanical properties as density and viscosity as well as optical properties such as the reflectivity of their surface.
Task 1.3. Characterisation of the candidate oils of Task 1.2, their density vs. temperature and pressure, viscosity as well as dynamics of gas saturation and degassing will be studied and, consequently, the best oil will be chosen.
Task 1.4. A system for in-situ density measurement will be developed and implemented in the oil-based micromanometer of Task 1.1.
Task 1.5. Characterisation of the complete oil-based interferometric micromanometer of Task 1.4 and evaluation of its performance including comparison against other pressure and vacuum standards.
The results of this WP will be used in WP3 and WP5.