ADVANCED FEED-FORWARD VALVE-CONTROL FOR A MASS FLOW CONTROLLER
The disclosed embodiments include a method, apparatus, and computer program product for measuring and controlling gas and/or liquid flow. In particular, embodiments of the invention provide advanced feed-forward valve-control for a mass flow controller for placing a proportional control valve in its expected position in response to a change in customer set point and/or an inlet pressures. In addition, the disclosed embodiments also provide independent ‘corroboration’ of the measured flow by a thermal mass flow sensor.
1 . A thermal mass flow controller for measuring flow of a fluid, comprising:
a thermal mass flow meter for providing a signal corresponding to mass flow through the flow meter, the flow meter including a flow sensor;
an adjustable valve for controlling the passage of fluid out of the mass flow controller;
a fluid path through the mass flow controller;
a pressure transducer for providing a signal corresponding to the fluid pressure at an inlet of the flow path; and
at least one processor configured to determine an expected valve position in response to at least one of a change in set point and inlet pressure, wherein the expected valve position is not based on the signal provided by the thermal mass flow meter; and
a controller to adjust the adjustable valve to the expected valve position to control the flow through the mass flow controller.
2 . The mass flow controller of claim 1 , wherein the at least one processor is configured to determine the expected valve position using a mathematical model of the valve involving a multivariable function.
3 . The mass flow controller of claim 1 , wherein the at least one processor is configured to magnetically derive a magnetic force from the adjustable valve itself.
4 . The mass flow controller of claim 3 , wherein the at least one processor is configured to measure the inductance of a solenoid coil of mass flow controller.
5 . The mass flow controller of claim 4 , wherein measuring the inductance of the solenoid coil is performed by imposing an AC current onto the solenoid ‘dc’ drive and capturing coil-voltage at a same frequency using a bandpass filter.
6 . The mass flow controller of claim 4 , wherein measuring the inductance of the solenoid coil is performed by phase-shifting (theta) of a superimposed high-frequency.
7 . The mass flow controller of claim 4 , wherein the at least one processor is further configured to determine a direct-measure of magnetic Air-Gap using the measured inductance.
8 . The mass flow controller of claim 3 , wherein the derived magnetic force is used to determine a flow rate.
9 . The mass flow controller of claim 8 , wherein the at least one processor is further configured to compare the determined flow rate to a second flow rate generated by the thermal mass flow meter.
10 . The mass flow controller of claim 1 , wherein the controller further adjusts the adjustable valve from the expected valve position to a second valve position based on the signal corresponding to mass flow provided by the thermal mass flow meter.
11 . The mass flow controller of claim 10 , wherein the at least one processor is further configured to:
determine a difference value between the expected valve position and the second valve position;
compare the difference value to a shutdown alarm threshold value; and
trigger a shutdown alarm in response to the difference value being greater than the shutdown alarm threshold value.
12 . The mass flow controller of claim 10 , wherein the at least one processor is further configured to:
determine a difference value between the expected valve position and the second valve position;
compare the difference value to a maintenance alarm threshold value; and
trigger a maintenance alarm in response to the difference value being greater than the shutdown maintenance threshold value.
13 . The mass flow controller of claim 1 further comprising memory for storing valve characteristic data produced by subjecting the adjustable valve to a multitude of flow rates and pressures.
14 . The mass flow controller of claim 13 , wherein the at least one processor uses the stored valve characteristic data in determining the solenoid current for the expected valve position.
15 . The mass flow controller of claim 2 , wherein the multivariable function assumes that the outlet pressure is ‘close’ to vacuum in determining the solenoid current for the expected valve position.
16 . The mass flow controller of claim 2 , wherein the multivariable function derives a relationship between magnetic-force, coil-milliamps, and air-gap/seat-lift.
17 . A method for a controlling a thermal mass flow controller, comprising:
calculating an expected valve position in response to at least one of a change in set point and inlet pressure, wherein the expected valve position is not based on a signal provided by a thermal mass flow meter of the thermal mass flow controller; and
adjusting an adjustable valve to the expected valve position to control flow through the mass flow controller.
18 . The method of claim 17 , wherein calculating the expected valve position utilizes a mathematical model of valve involving a multivariable function.
19 . The method of claim 17 , wherein calculating the expected valve position includes deriving a magnetic force magnetically from the adjustable valve itself.
20 . A computer program product embodied on a tangible computer readable medium having instructions thereon that when executed causes a thermal mass flow controller to:
determine an expected valve position in response to at least one of a change in set point and inlet pressure, wherein the expected valve position is not based on a signal provided by a thermal mass flow meter of the thermal mass flow controller;
adjust an adjustable valve to the expected valve position to control flow through the mass flow controller; and
compare the expected valve position to a second valve position based on a signal corresponding to mass flow provided by a thermal mass flow meter of the mass flow controller.