Multi-gas mass flow controller and method

1. A method for controlling a mass flow controller, the method comprising:

providing a process gas through a flow sensor of the mass flow controller;

obtaining a gas-adjusted sensitivity coefficient for the flow sensor;

obtaining gas-adjusted nonlinearity data for the flow sensor;

producing gas-adjusted characterization data for the flow sensor using the gas-adjusted sensitivity coefficient and the gas-adjusted nonlinearity data;

obtaining a flow value from the gas-adjusted characterization data using a flow sensor signal from the flow sensor; and

using the flow value along with a setpoint signal to control a valve of the mass flow controller.

2. The method of claim 1 , wherein obtaining the gas-adjusted sensitivity coefficient includes:

retrieving a sensitivity coefficient for the flow sensor, the sensitivity coefficient representing an ideal signal of the flow sensor when the flow sensor is used with a characterization gas;

retrieving a conversion factor for the process gas from a memory of the mass flow controller; and

adjusting the sensitivity coefficient with the conversion factor to obtain the gas-adjusted sensitivity coefficient.

3. The method of claim 2 , wherein obtaining the gas-adjusted nonlinearity data for the flow sensor includes:

retrieving nonlinearity data associated with characterization gas for the flow sensor;

retrieving a nonlinearity factor for the process gas from a memory of the mass flow controller; and

adjusting the nonlinearity data for the flow sensor with the nonlinearity factor for the process gas to obtain the gas-adjusted nonlinearity data, wherein the nonlinearity data is previously produced in connection with a characterization gas.

4. The method of claim 1 , wherein the gas-adjusted sensitivity coefficient is produced by:

obtaining a sensitivity coefficient for a characterization gas and dividing the sensitivity coefficient for the characterization gas by a conversion factor for the process gas.

5. The method of claim 1 , wherein:

the gas-adjusted characterization data is represented by: {(f i , s i /CF+NLF*z i )|i=1, 2, . . . , n} where CF is a conversion factor for the process gas, NLF is a gas-specific nonlinearity factor, s i =SC*f i where f i are flow values, z i are nonlinearity values equal to s i minus y i where y i are signal values of characterization data for a characterization gas, the characterization data represented by: {(f i ,y i )|i=1, 2, . . . , n}.

6. A mass flow controller comprising:

a main flow path for a gas;

a control valve to control a flow rate of the gas through the main flow path;

a flow sensor coupled to the main flow path to provide a flow sensor signal indicative of a mass flow rate of the gas;

a sensitivity adjustment module configured to adjust a sensitivity coefficient with a conversion factor for a process gas to produce a gas-adjusted sensitivity coefficient for the flow sensor, the sensitivity coefficient representing an ideal signal of the flow sensor when the flow sensor is used with a characterization gas;

a nonlinearity adjustment module configured to adjust nonlinearity data associated with a characterization gas for the flow sensor with a nonlinearity factor for the process gas to produce gas-adjusted nonlinearity data, the nonlinearity data previously produced in connection with a characterization gas;

a characterization module configured to:

produce gas-adjusted characterization data for the flow sensor using the gas-adjusted sensitivity coefficient and the gas-adjusted nonlinearity data; and

obtain a flow value from the gas-adjusted characterization data using a flow sensor signal from the flow sensor; and

a controller configured to use the flow value along with a setpoint signal to control a valve of the mass flow controller.

7. The mass flow controller of claim 6 including nonvolatile memory including the sensitivity coefficient, the nonlinearity data, the conversion factor, and the nonlinearity factor.

8. The mass flow controller of claim 6 including an interface component configured to receive the conversion factor and the nonlinearity factor via a network connection.