Fluid flow controlling

A fluid flow controller for controlling the rate of flow of a fluid comprising:

• a first fluid flow passage having an inlet and an outlet;
• a first flow restrictor comprising a three-dimensional porous structure defining a through-flow matrix including a plurality of pores and having known and substantially constant pressure drop-flow rate characteristics positioned in said flow passage and the flow rate being characterized by at least one other process parameter in addition to pressure drop;
• an upstream pressure sensor for determining the pressure of gas in said flow passage upstream of said flow restrictor;
• and
• a downstream pressure sensor for determining the pressure of gas in said flow passage downstream of said flow restrictor.

A fluid flow controller comprising:

• a first fluid flow passage having an inlet and an outlet;
• a first flow restrictor comprising a three-dimensional porous structure defining a through-flow matrix including a plurality of pores and having known pressure drop-flow rate characteristics positioned in said flow passage and the flow rate being characterized by at least one other process parameter in addition to pressure drop;
• an upstream pressure sensor for determining the pressure of gas in said flow passage upstream of said flow restrictor;
• a downstream pressure sensor for determining the pressure of gas in said flow passage downstream of said flow restrictor;
• and
• a second flow passage having an inlet communicating with said first flow passage upstream of said flow restrictor wherein said second flow passage is connected in parallel with the portion of said first flow passage in which said flow restrictor is positioned.