System for and method of monitoring flow through mass flow controllers in real time

A mass flow controller comprising:

• a first, thermal mass flow meter operative to measure flow rate of mass of gas through the mass flow controller in real time during the running of a process, and to produce a first flow measurement signal representing a measured flow rate through the mass flow controller;
• a differential pressure flow meter including (i) a flow restrictor disposed in a flow path of the mass flow controller, (ii) a pressure sensor operative to sense pressure in the flow path of the mass flow controller upstream of the flow restrictor, and (iii) a temperature sensor operative to sense temperature of the flow path upstream of the flow restrictor;
• wherein the differential pressure flow meter is operative to measure flow rate of mass of gas through the mass flow controller, and to produce as an output a second flow measurement signal based on data from the pressure sensor and the temperature sensor;
• a control valve disposed between the first, thermal mass flow meter and the differential pressure flow meter, with the first, thermal mass flow meter upstream of the control valve and the differential pressure flow meter downstream of the control valve, the control valve operative to control the flow rate of mass of gas through the mass flow controller in response to a control signal generated as a function of the flow rate as measured by one of the flow meters during the running of the process;
• and
• a system controller operative to receive the first and second flow measurement signals produced by the first and differential pressure flow meters, respectively, and to generate the control signal, and to provide an alarm signal indicating when a difference between the first and second flow measurement signals exceeds a predetermined threshold.