ADVANCED FEED-FORWARD VALVE-CONTROL FOR A MASS FLOW CONTROLLER

• US 20120197446A1
• Filed: 12/01/2011
• Published: 08/02/2012
• Est. Priority Date: 12/01/2010
• Status: Abandoned Application

• Current Assignee: Brooks Instrument LLC (Illinois Tool Works Inc.)
• Original Assignee: Brooks Instrument LLC (Illinois Tool Works Inc.)
• Inventors: Glaudel, Stephen P.
• Application Number:
  US13/309,338
• Publication Number:
  US 20120197446A1
• Time in Patent Office: Days
• US Class Current: 700/282
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

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.

Claims

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.