In order to prepare an intercomparison of national measurement standards for low differential pressures, a generator of defined pressure differences has been designed, developed and tested. The pressure generator can produce 15 differential pressures in the range of 0 to 1000 Pa, superimposed on ambient air pressure. The testing of the instrument included the determination of this repeatability and the influences of environmental conditions.
The measurement of low differential pressure frequently forms an essential part of the measurement of the flow of gases, particularly natural gas and air. Normally, in the case of gas, precautions are taken to ensure that the differential pressure to be measured does not fall below a nominal value, such as 100 Pa. For applications in the fields of heating and ventilating engineering, aircraft instrumentation, aerodynamic research and the leak testing of enclosures for delicate instruments or hazardous materials, such an option may not exist. It is therefore necessary to be able to make measurements throughout the differential pressure range zero to 1000 Pa with a precision of + (0.1 Pa + 0.01 % of the reading).
The initial stage will consist of constructing a transfer standard in which a series of fixed differential pressures will be generated across sonic nozzles of different throat diameters whose flow rates are determined solely by the pressure and temperature of the gas on their inlet sides. After the device has been fully characterized it will be circulated to the participating laboratories for comparison with the instruments that they usually use for calibration purposes.
Funding SchemeCSC - Cost-sharing contracts
G75 0QU Glasgow
TW11 0LW Teddington