Conventional pressure balances as reference standards for pressures in the range 10 Pa to 10 kPa

Two methods are presented for using conventional pressure balances in the pressure range 10 Pa to 10 kPa. Both these methods overcome the inability of a pressure balance to generate directly pressures below a limit determined by the mass of the floating element. The first method uses twin pressure balances, with the desired low pressure established above one pressure balance in terms of a small added mass on the other pressure balance. This method is shown to be capable of realizing low absolute pressures with a standard uncertainty below 2 mPa + (9 x 10(-6))p, when operating the pressure balances at 100 kPa. The second method uses one pressure balance in conjunction with a high-resolution pressure gauge. A calculable low pressure is established above the pressure balance either by reference to an added mass on the pressure balance or by a change in the pressure gauge reading. A 100 kPa pressure balance is used in combination with a commercial high-precision barometric pressure gauge, modified to improve the temperature control of its sensor. The standard uncertainty associated with this implementation is shown to be about 14 mPa+(9 x 10(-6))p.