MEASUREMENT UNCERTAINTIES OF U-TUBE MANOMETERS AND PRESSURE BALANCES

Following the advent of the BIPM Recommendation of 1981 and the ISO Guide of 1993, it should be possible to achieve much greater consistency in the ways in which the measurement uncertainties of pressure standards are evaluated and expressed. These documents divide uncertainty contributions into two groups, type A (random) and type B (others). The method of evaluating and combining uncertainty contributions is illustrated by two examples - a U-tube manometer and a pressure balance (piston gauge). In both cases the uncertainty contributions are subdivided into two further groups - those which are independent of the applied pressure and those which are proportional to it.