SYSTEM AND METHOD FOR IMPROVED INDICATED FLOW IN MASS FLOW CONTROLLERS

• US 20140257720A1
• Filed: 01/20/2014
• Published: 09/11/2014
• Est. Priority Date: 03/08/2013
• Status: Active Grant

• Current Assignee: Hitachi Metals (Thailand) Ltd.
• Original Assignee: Hitachi Metals (Thailand) Ltd.
• Inventors: Smirnov, Alexei V.
• Granted Patent: US 10,473,500 B2
• Time in Patent Office: Days
• US Class Current: 702/45
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• 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 15/002 for gases
• CPC Class Codes: G01F 15/005 Valves valves in general F16K
• CPC Class Codes: G01F 5/00 Measuring a proportion of the volume flow
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

A mass flow controller and associated methods for providing indicated flow from the mass flow controller are disclosed. The method may include obtaining a measured flow signal indicative of a mass flow rate of a fluid that is controlled by the mass flow controller and filtering the measured flow signal to generate indicated flow that provides a representation of the actual mass flow rate of the fluid. The indicated flow is provided to an operator of the mass flow controller, and a rate of change of the mass flow rate of the fluid is determined based upon samples of the measured flow signal. A time constant used in connection with the filtering is then adjusted based upon the rate of change of the mass flow rate.

Claims

1. A method for providing indicated flow from a mass flow controller, the method comprising:

obtaining a measured flow signal indicative of a mass flow rate of a fluid that is controlled by the mass flow controller;

filtering the measured flow signal to generate indicated flow that provides a representation of an actual mass flow rate of the fluid;

providing the indicated flow to an operator of the mass flow controller;

sampling the measured flow signal and determining a rate of change of the mass flow rate of the fluid based upon samples of the measured flow signal; and

adjusting a time constant used in connection with the filtering based upon the rate of change of the mass flow rate.

2. The method of claim 1, including:

increasing the time constant until a maximum time constant is reached or until the rate of change of the mass flow rate exceeds a threshold.

3. The method of claim 2, including, when there is a set point change to a new set point:

reducing the time constant;

initiating a timer to track a time that has transpired since the time constant was reduced; and

maintaining the time constant at a reduced level until the time that has transpired reaches a time threshold or until the measured flow rate either exceeds the set point if the new set point is an increase in the set point or the measured flow rate drops below the set point if the new set point is a decrease in the set point.

4. The method of claim 3, including:

maintaining the time constant at the reduced level until the measured flow rate;

exceeds the set point and then drops below the set point if the new set point is an increase in the set point;

or

drops below the set point and then exceeds the set point if the new set point is a decrease in the set point.

5. The method of claim 1 including, when a set point changes to a new set point:

retaining a last value of the indicated flow in memory as a reference point, wherein the last value of the indicated flow is a mass flow rate provided with as the indicated flow;

performing, while a measured flow rate has not reached the new set point, a smoothing operation including;

providing the reference point to the operator as the indicated flow if the measured flow rate is less than the reference point; and

setting, if the measured flow rate is not less than the reference point, the reference point to the measured flow rate and providing the reference point to the operator as the indicated flow.

6. A mass flow controller comprising:

a mass flow sensor that provides a measured flow signal indicative of a mass flow rate of a fluid;

a processor to receive the measured flow signal and provide an indicated flow output; and

a non-transitory, tangible processor readable storage medium coupled to the processor and encoded with processor readable instructions for filtering the measured flow signal to provide the indicated flow output, the instructions comprising instructions for;

determining a rate of change of the mass flow rate of the fluid based upon the measured flow signal; and

adjusting a time constant used in connection with the filtering based upon the rate of change of the mass flow rate.

7. The mass flow controller of claim 6, wherein the non-transitory, tangible processor readable storage medium is encoded with processor readable instructions that includes instructions for increasing the time constant until a maximum time constant is reached or until the rate of change of the mass flow rate exceeds a threshold.

8. The mass flow controller of claim 7, wherein the non-transitory, tangible processor readable storage medium is encoded with processor readable instructions that include instructions for, when there is a set point change to a new set point:

reducing the time constant;

initiating a timer to track a time that has transpired since the time constant was reduced; and

maintaining the time constant at a reduced level until the time that has transpired reaches a time threshold or the measured flow rate either exceeds the set point if the new set point is an increase in the set point or drops below the set point if the new set point is a decrease in the set point.

9. The mass flow controller of claim 8, wherein the non-transitory, tangible processor readable storage medium is encoded with processor readable instructions that include instructions for:

maintaining the time constant at the reduced level until the measured flow rate;

exceeds the set point and then drops below the set point if the new set point is an increase in the set point;

or

drops below the set point and then exceeds the set point if the new set point is a decrease in the set point.

10. The mass flow controller of claim 6, wherein the non-transitory, tangible processor readable storage medium is encoded with processor readable instructions that include instructions for, when a set point changes to a new set point:

storing a last indicated flow value in memory as a reference point, wherein the last indicated flow value is a mass flow rate value provided as the indicated flow output;

performing, while a measured flow rate has not reached the new set point, a smoothing operation including;

providing the reference point as the indicated flow output if the measured flow rate is less than the reference point; and

setting, if the measured flow rate is not less than the reference point,

the reference point to the measured flow rate and providing the reference point as the indicated flow output.

11. A mass flow controller comprising:

means for obtaining a measured flow signal indicative of a mass flow rate of a fluid that is controlled by the mass flow controller;

means for filtering the measured flow signal to generate indicated flow that provides a representation of the actual mass flow rate of the fluid;

means for providing the indicated flow to an operator of the mass flow controller;

means for sampling the measured flow signal and determining a rate of change of the mass flow rate of the fluid based upon samples of the measured flow signal; and

means for adjusting a time constant used in connection with the filtering based upon the rate of change of the mass flow rate.

12. The mass flow controller of claim 11, including:

means for increasing the time constant until a maximum time constant is reached or until the rate of change of the mass flow rate exceeds a threshold.

13. The mass flow controller of claim 12, including,

when there is a set point change to a new set point:

means for reducing the time constant;

means for initiating a timer to track a time that has transpired since the time constant was reduced; and

means for maintaining the time constant at a reduced level until the time that has transpired reaches a time threshold or until the measured flow rate either exceeds the set point if the new set point is an increase in the set point or the measured flow rate drops below the set point if the new set point is a decrease in the set point.

14. The mass flow controller of claim 13, including:

means for maintaining the time constant at the reduced level until the measured flow rate;

exceeds the set point and then drops below the set point if the new set point is an increase in the set point;

or

drops below the set point and then exceeds the set point if the new set point is a decrease in the set point.

15. The mass flow controller of claim 14 including, when a set point changes:

means for storing a last indicated flow value in memory as a reference point, wherein the last indicated flow value is a mass flow rate value provided as the indicated flow;

means for performing, while a measured flow rate has not reached the new set point, a smoothing operation including;

means for providing the reference point as the indicated flow if the measured flow rate is less than the reference point; and

means for setting, if the measured flow rate is not less than the reference point, the reference point to the measured flow rate and providing the reference point as the indicated flow.