Mass flow controller and method for controlling a mass flow rate of a gas in a gas stream
Systems and method for detecting a concentration of a gas in a gas stream are disclosed. A method includes receiving a gas stream including a carrier gas and a processing gas. Bridge signals of a mass flow sensor are used to produce a processing-gas concentration signal and a gas-stream mass flow rate signal. The gas stream is controlled so a mass flow rate of the processing gas equals a processing-gas-setpoint signal. In some variations, the processing-gas-concentration signal is produced using an upstream temperature of the gas stream and a bridge-derived temperature.
1. A mass flow controller comprising:
a main flow path for a gas stream, the gas stream including a processing gas and a carrier gas;
a temperature sensor disposed and configured to obtain an upstream temperature of the gas stream and provide an upstream temperature signal indicative of the upstream temperature;
a thermal mass flow sensor coupled to the main flow path, wherein the thermal mass flow sensor is configured to provide a bridge-derived temperature signal indicative of a bridge-derived temperature and a gas-stream-flow-rate signal indicative of a mass flow rate of the gas stream;
a gas concentration meter disposed to receive the bridge-derived temperature signal, and the gas concentration meter is configured to provide a processing-gas-concentration signal based upon the bridge-derived temperature 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.
2. The mass flow controller of claim 1 , wherein the thermal mass flow sensor includes:
a sensor tube coupled to the main flow path;
at least two sensing elements coupled to the sensor tube, wherein the at least two sensor elements are arranged in a bridge circuit;
a bridge-derived temperature module configured generate the bridge-derived temperature signal; and
a differential-voltage processing module configured to produce the gas-stream-flow-rate signal based upon a differential voltage of the bridge circuit.
3. The mass flow controller of claim 1 , wherein the gas concentration meter is configured to:
obtain a temperature-difference between the upstream temperature of the gas stream and the bridge-derived temperature; and
utilize the temperature-difference to lookup a concentration value for the processing gas.
4. The mass flow controller of claim 1 , wherein the gas concentration meter is configured to:
obtain the temperature-difference between the upstream temperature of the gas stream and the bridge-derived temperature; and
utilize the temperature-difference to calculate the concentration value for the processing gas.
5. A mass flow control system comprising:
a conduit to receive a gas stream including a carrier gas and a processing gas;
a thermal mass flow sensor disposed to receive the gas stream from the conduit, wherein the thermal mass flow sensor is configured to provide a bridge-derived temperature signal indicative of a bridge-derived temperature and a gas-stream-flow-rate signal;
a gas concentration meter disposed to receive the bridge-derived temperature signal and the gas-stream-flow-rate signal, and the gas concentration meter is configured to provide a processing-gas-concentration signal based upon the bridge-derived temperature signal and a gas-stream-flow-rate 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.
6. The mass flow control system of claim 5 , wherein the thermal mass flow sensor includes:
a sensor tube coupled to the conduit;
at least two sensing elements coupled to the sensor tube, wherein the at least two sensor elements are arranged in a bridge circuit;
a top voltage processing module configured generate the bridge-derived temperature signal using a top voltage of the bridge;
a differential-voltage processing module configured to produce the gas-stream-flow-rate signal based upon a differential voltage of the bridge circuit.
7. The mass flow control system of claim 5 , including:
a vaporizer including:
an input to receive the carrier gas;
a chamber to produce the processing-gas from a material source; and
an output coupled to the conduit to provide the gas stream.
8. The mass flow control system of claim 5 , wherein the gas concentration meter is configured to:
utilize the bridge-derived temperature signal and the gas-stream-flow-rate signal to lookup a concentration value for the processing gas.
9. The mass flow control system of claim 5 , wherein the gas concentration meter is configured to:
utilize the bridge-derived temperature signal and the gas-stream-flow-rate signal to calculate the concentration value for the processing gas.