System and method for detecting concentration of a gas in a gas stream

A mass flow control system comprising:

• a conduit to receive a gas stream including a carrier gas and a processing gas;
• a temperature sensor thermally coupled to the conduit to obtain an upstream temperature of the gas stream and provide an upstream temperature signal indicative of the upstream temperature;
• a thermal mass flow meter disposed to receive the gas stream from the conduit, wherein the thermal mass flow sensor is configured to provide a gas-stream-flow-rate signal and a bridge-derived temperature signal indicative of a bridge-derived temperature;
• a gas concentration meter disposed to receive the upstream temperature signal and the bridge-derived temperature signal, and the gas concentration meter is configured to provide a processing-gas-concentration signal;
• a processing-gas mass flow meter disposed to receive the processing-gas-concentration signal and the gas-stream-flow-rate signal, wherein the processing-gas mass flow meter is configured to provide a processing-gas-mass-flow-rate signal;
• a control valve coupled to the conduit to control a mass flow rate of the gas stream;
• and
• a controller disposed to receive the processing-gas-mass-flow-rate signal and adjust the control valve so the processing-gas-mass flow rate equals a processing-gas-setpoint signal.