Methods and apparatuses for delivering a process gas to a processing chamber are provided. A mass flow controller includes a first flow line for introducing a process fluid and an inlet valve disposed along the first flow line for controlling a flow rate of the process fluid. The mass flow controller includes a second flow line for introducing a carrier fluid into the mass flow controller and a micro-electro-mechanical system (MEMS) Coriolis sensor for providing a density signal and a mass flow rate signal for a mixture of the process fluid and the carrier fluid. The mass flow controller provided includes an outlet valve for controlling a mass flow rate of the mixture that is output by the mass flow controller as well as a controller for operating the inlet valve based on the density signal and for operating the outlet valve based on the mass flow rate signal.

Methods and apparatuses for delivering a process gas to a processing chamber are provided. A mass flow controller includes a first flow line for introducing a process fluid and an inlet valve disposed along the first flow line for controlling a flow rate of the process fluid. The mass flow controller includes a second flow line for introducing a carrier fluid into the mass flow controller and a micro-electro-mechanical system (MEMS) Coriolis sensor for providing a density signal and a mass flow rate signal for a mixture of the process fluid and the carrier fluid. The mass flow controller provided includes an outlet valve for controlling a mass flow rate of the mixture that is output by the mass flow controller as well as a controller for operating the inlet valve based on the density signal and for operating the outlet valve based on the mass flow rate signal.

A pressure reducer, comprising an outer cylinder with a first air supply connector on a first end side of the outer cylinder and a second air supply connector on a second end side of the outer cylinder is provided. A piston can be guided movably in the outer cylinder. A first air chamber is arranged between the first air supply connector of the outer cylinder and the first front surface of the piston, and a second air chamber is arranged between the second air supply connector of the outer cylinder and a second front surface of the piston. The surface areas of the two front surfaces of the piston are of different size. The pressure reducer is suitable for reducing a second air pressure which prevails in the second air chamber in a pulsed manner proportionally to a first air pressure which prevails in the first air chamber, by a first air connection.

There is provided a gas mixer arrangement comprising a first gas source for supplying a first gas; a second gas source for supplying a second gas different from said first gas; a first valve for regulating the flow of the first gas; a second valve for regulating the flow of the second gas; a mixer located downstream of the first and second valves and arranged, in use, to mix the first and second gases to provide a mixed gas; a meter arranged to measure the average molecular weight of the mixed gas, comprising a high-frequency planar piezoelectric crystal oscillator in contact with the mixed gas and a sensor operable to determine atmospheric pressure; and a controller operable, in response to the measured average molecular weight of said mixed gas, to control at least one of said first and second valves in order to control the relative proportion of the first and second gases in said mixed gas.