Mass flow controller apparatus

Claim 1

An apparatus capable of selecting and controlling the mass flow rate of gas through a conduit to be substantially constant over a period of at least 4 hours and within a mass flow rate range of from about 0.05 to about 0.5 ml/min at standard temperature and pressure conditions and a gas partial pressure range of from about 0.03 to 1 which comprises: an enclosure having an exterior surface and defining an inner space; means for controlling the temperature within said inner space to be substantially constant; first conduit means defining an input path for directing the flow of a gas from an input port disposed at the exterior surface of said enclosure into said inner space, and an output path in fluid communication with said input path for directing the flow of said gas out of said inner space to an output port at the exterior surface of said enclosure; elongate sensing conduit means disposed within said enclosure inner space having an interior channel for directing the flow of a gas therethrough and having an input and an output; the input of said sensing conduit being engaged in fluid communication with the input path of said first conduit means and the output of said sensing conduit being engaged in fluid communication with the output path of said first conduit means, the diameter of said sensing conduit interior channel being not greater than 0.2 mm; flow meter means disposed within said enclosure inner space and in contact with said sensing conduit for sensing a temperature differential induced by change in the mass flow rate of a gas passing from the input to the output of said sensing conduit, and for generating a first output signal representative of said temperature differential and proportional to the mass flow rate of said gas passing through said sensing conduit; means for generating a reference second output signal proportional to a selected mass flow rate of a gas; means disposed within said enclosure inner space for comparing the first and second output signals and generating a third output signal representative of the difference of said first and second output signals; valve means, disposed within said enclosure inner space engaged with said sensing conduit downstream of said flow meter means and with the output path of said first conduit means for controllably disengaging the fluid communication between the sensing conduit and the output path of said first conduit means thereby permitting regulation of the mass flow rate of a gas passing from said sensing conduit to the output path of said first conduit means, said valve means being actuated by said third output signal; means for permitting the temperature of a gas passing through the input path of said first conduit means to equilibrate with the substantially constant temperature of said enclosure inner space before said gas enters the sensing conduit means; means for controlling the pressure of a gas as it enters the input of said sensing conduit means to be substantially constant.

Claim 2

An apparatus capable of selecting and controlling the mass flow rate of gas through a conduit to be substantially constant over a period of at least 4 hours and within a mass flow rate range of from about 0.05 to about 0.5 ml/min at standard temperature and pressure conditions and a gas partial pressure range of from about 0.03 to 1 which comprises: an enclosure having an exterior surface and defining an inner space; means for controlling the temperature within said inner space to be substantially constant; first conduit means defining an input path for directing the flow of a gas from an input port disposed at the exterior surface of said enclosure into said inner space, and an output path in fluid communication with said input path for directing the flow of said gas out of said inner space to an output port at the exterior surface of said enclosure; elongate sensing conduit means disposed within said enclosure inner space having an interior channel for directing the flow of a gas therethrough and having an input and an output; the input of said sensing conduit being engaged in fluid communication with the input path of said first conduit means and the output of said sensing conduit being engaged in fluid communication with the output path of said first conduit means, the diameter of said sensing conduit interior channel being not greater than 0.2 mm; flow meter means disposed within said enclosure inner space and in contact with said sensing conduit for sensing a temperature differential induced by change in the mass flow rate of a gas passing from the input to the output of said sensing conduit, and for generating a first output signal representative of said temperature differential and proportional to the mass flow rate of said gas passing through said sensing conduit; means for generating a reference second output signal proportional to a selected mass flow rate of a gas; means disposed within said enclosure inner space for comparing the first and second output signals and generating a third output signal representative of the difference of said first and second output signals; valve means, disposed within said enclosure inner space engaged with said sensing conduit downstream of said flow meter means and with the output path of said first conduit means for controllably disengaging the fluid communication between the sensing conduit and the output path of said first conduit means thereby permitting regulation of the mass flow rate of a gas passing from said sensing conduit to the output path of said first conduit means, said valve means being actuated by said third output signal; means for permitting the temperature of a gas passing through the input path of said first conduit means to equilibrate with the substantially constant temperature of said enclosure inner space before said gas enters the sensing conduit means; means for controlling the pressure of a gas as it enters the input of said sensing conduit means to be substantially constant.