ABSTRACT
The knowledge of gas throughput or mass flow rate is vital in vacuum technology because of the design of a vacuum system, the determination of conductance of vacuum components, pumping speed, and control of technological processes and their efficiency. Gases are admitted into vacuum in a controlled way. Devices for the measurement of gas flow rates are called flowmeters, which can measure the gas amount flowing into a system per unit time by volumetric methods, in which the gas volume entering a vacuum system per second is measured at known pressure and temperature. Alternatively, the measurement can be carried out by gravimetric methods, in which the gas mass entering a vacuum system is weighted. Gas flow rate can be determined by gas accumulation or diminishing methods in metering systems. Gas flow rate can be determined using a calibrated conductance of an aperture and measuring the pressure difference across the aperture.
