THERMAL MASS FLOW SENSOR WITH IMPROVED ACCURACY

• US 20190331515A1
• Filed: 04/03/2019
• Published: 10/31/2019
• Est. Priority Date: 04/27/2018
• Status: Active Grant

• Current Assignee: Hitachi Metals (Thailand) Ltd.
• Original Assignee: Hitachi Metals (Thailand) Ltd.
• Inventors: Smirnov, Alexei V.
• Granted Patent: US 11,209,298 B2
• Time in Patent Office: Days
• CPC Class Codes: G01F 1/6847 where sensing or heating elements are not disturbing the fluid flow, e.g. elements mounted outside the flow duct
• CPC Class Codes: G01F 1/6965 comprising means to store calibration data for flow signal calculation or correction
• CPC Class Codes: G01F 15/005 Valves valves in general F16K
• CPC Class Codes: G01F 25/15 specially adapted for gas meters G01F25/11 - G01F25/14, G01F25/17 take precedence
• CPC Class Codes: G01F 5/00 Measuring a proportion of the volume flow
• CPC Class Codes: G01K 7/14 Arrangements for modifying the output characteristic, e.g. linearising
• CPC Class Codes: G01K 7/42 Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

Mass flow controllers and methods for controlling mass flow controllers are disclosed. A method includes providing a gas through a thermal mass flow sensor of the mass flow controller and processing a flow sensor signal from the thermal mass flow sensor of the mass flow controller to produce a measured flow signal. The measured flow signal is corrected to produce a corrected flow signal by gradually applying non-linearity correction to the measured flow signal when a flow rate of the gas changes. A valve of the mass flow controller is controlled using the corrected flow signal and a setpoint signal.

Claims

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

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

processing a flow sensor signal from the thermal mass flow sensor of the mass flow controller to produce a measured flow signal;

correcting the measured flow signal to produce a corrected flow signal by gradually applying non-linearity correction to the measured flow signal when a flow rate of the gas changes; and

controlling a valve of the mass flow controller using the corrected flow signal and a setpoint signal.

2. The method of claim 1, wherein the processing includes utilizing steady-state-derived nonlinearity characterization data to adjust the flow sensor signal to produce the measured flow signal;

and

the correcting includes obtaining a product of the measured flow signal and a predicted sensor sensitivity value, S_p, while the predicted sensor sensitivity value, S_p, gradually changes toward a current sensor sensitivity value.

3. The method of claim 2, wherein the predicted sensor sensitivity value, S_p=k*S_c+(1−

k)*S_p, where k=t_s/T, where t_s is a sampling interval between obtaining flow rates and T is a time constant.

4. The method of claim 3, wherein the time constant, T, is two seconds or less.

5. The method of claim 1, wherein gradually applying includes adjusting a sensor sensitivity function that is used to adjust the measured flow signal for up to 10 seconds.

6. The method of claim 5 wherein gradually applying includes adjusting a sensor sensitivity function that is used to adjust the measured flow signal for up to 8 seconds.

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

means for processing the flow sensor signal from the thermal mass flow sensor of the mass flow controller to produce a measured flow signal;

means for correcting the measured flow signal to produce a corrected flow signal by gradually applying non-linearity correction to the measured flow signal when a flow rate of the gas changes; and

a control component coupled to the means for correcting and the control valve to control a position of the control valve based upon the corrected flow signal and a setpoint signal.

8. The mass flow controller of claim 7, wherein the means for processing includes means for utilizing steady-state-derived nonlinearity characterization data to adjust the flow sensor signal to produce the measured flow signal;

and

the means for correcting includes means for obtaining a product of the measured flow signal and a predicted sensor sensitivity value, S_p, while the predicted sensor sensitivity value, S_p, gradually changes toward a current sensor sensitivity value.

9. The mass flow controller of claim 8, wherein the predicted sensor sensitivity value, S_p=k*S_c+(1−

k)*S_p, where k=t_s/T, where t_s is a sampling interval between obtaining flow rates and T is a time constant.

10. The mass flow controller of claim 9, wherein the time constant, T, is two seconds or less.

11. The mass flow controller of claim 7, wherein the means for gradually applying includes means for adjusting a sensor sensitivity function that is used to adjust the measured flow signal for up to 10 seconds.

12. The mass flow controller of claim 11 wherein the means for gradually applying includes means for adjusting a sensor sensitivity function that is used to adjust the measured flow signal for up to 8 seconds.

13. A mass flow controller comprising:

a main flow path for a gas;

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

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

a processing portion to receive and process the flow sensor signal from the thermal mass flow sensor to produce a measured flow signal;

a nonlinear compensator including a non-transitory, tangible processor readable storage medium, encoded with processor executable instructions to produce a corrected flow signal, the instructions comprising instructions to;

correct the measured flow signal to produce the corrected flow signal by gradually applying non-linearity correction to the measured flow signal when a flow rate of the gas changes; and

a control component coupled to the nonlinear compensator and the control valve to control a position of the control valve based upon the corrected flow signal and a setpoint signal.

14. The mass flow controller of claim 13, wherein the processing portion is configured to utilize steady-state-derived nonlinearity characterization data to adjust the flow sensor signal to produce the measured flow signal;

and

the instructions to correct includes instructions to obtain a product of the measured flow signal and a predicted sensor sensitivity value, S_p, while the predicted sensor sensitivity value, S_p, gradually changes toward a current sensor sensitivity value.

15. The mass flow controller of claim 14, wherein the predicted sensor sensitivity value, S_p=k*S_c+(1−

k)*S_p, where k=t_s/T, where t_s is a sampling interval between obtaining flow rates and T is a time constant.

16. The mass flow controller of claim 15, wherein the time constant, T, is two seconds or less.

17. The mass flow controller of claim 13, wherein gradually applying includes adjusting a sensor sensitivity function that is used to adjust the measured flow signal for up to 10 seconds.

18. The mass flow controller of claim 17 wherein gradually applying includes adjusting a sensor sensitivity function that is used to adjust the measured flow signal for up to 8 seconds.