A 2D flow model is described for calculation of the effective area (<em>A</em>) of pressure-measuring piston-cylinder units (PCU) based on their dimensional properties. With the 2D model, the uncertainty contribution associated with PCU's axial non-symmetry can be eliminated and the uncertainty of <em>A</em> can be reduced. The 2D model is applied to several primary PCUs operated in absolute and gauge pressure modes with different pressure-transmitting media. The benefit of the 2D model in dependence on PCU's geometrical perfectness is discussed.
At PTB, a new interferometric oil manometer for the measurement of pressures below 2 kPa, is in development. This paper describes how the main quantities, length and liquid density, are determined, both in-situ, the latter for the first time in a primary pressure standard. The key features of both methods are presented.
The measurement of negative gauge pressure is a field of increasing importance in science and industry. One of the main aims of the EMPIR Joint Research Project 14IND 06 pres2vac is to develop guidelines for it. We present a comparison of three different methods for measuring negative gauge pressure: (i) using two absolute pressure measuring instruments, (ii) generating a negative gauge pressure in the bell jar of the pressure balance, and (iii) using a 'hanging piston' pressure balance. The advantages and drawbacks are discussed and some preliminary results presented.
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