System and method for output compensation in flow sensors using pulse width modulation

Patent metadata

Field	Value
Publication number	US-10558227-B2
Application number	US-201815908041-A
Country	US
Kind code	B2
Filing date	Feb 28, 2018
Priority date	Feb 15, 2018
Publication date	Feb 11, 2020
Grant date	Feb 11, 2020

Abstract

A system for monitoring and controlling flow rate of a fluid through a valve is disclosed. The system includes a flow rate sensor to measure the flow rate of the fluid through the valve, and a controller. The controller is configured to receive the measured flow rate from the flow rate sensor, and determine if the measured flow rate is equal to a predetermined flow rate value. The controller is further configured to, in response to a determination that the measured flow rate is equal to the predetermined flow rate value, determine a minimum valve position threshold (xmin). Additionally, the controller is configured to determine a minimum flow rate threshold (ymin) corresponding to xmin, and configured to generate a PWM signal and calculate a corrected flow rate (ŷf) using the PWM signal. The controller controls a valve operation using ŷf. The PWM signal switches between zero and ymin.

First claim

What is claimed is:

1. A system for monitoring and controlling flow rate of a fluid through a valve, the system comprising:
a flow rate sensor configured to measure the flow rate of the fluid through the valve; and
a controller in communication with the flow rate sensor and configured to:
receive the measured flow rate from the flow rate sensor;
determine if the measured flow rate is equal to a predetermined flow rate value; and
in response to a determination that the measured flow rate is equal to the predetermined flow rate value:
determine a minimum valve position threshold (x min );
determine a minimum flow rate threshold (y min ) corresponding to x min ;
generate a pulse-width modulated (PWM) signal;
calculate a corrected flow rate (ŷ f ) using the PWM signal; and
control a valve operation using the corrected flow rate (ŷ f );

wherein the PWM signal is configured to switch between zero and y min .

2. The system of claim 1 , wherein the PWM signal is equal to zero when a pulse run time (t r ) is between a sum of a beginning of a pulse period (t k ) and a pulse width (T on ) and a sum of the beginning of the pulse period (t k ) and a pulse period (C).

3. The system of claim 1 wherein the PWM signal is equal to y min when a pulse run time (t r ) is between the beginning of a pulse period (t k ) and a sum of the beginning of the pulse period (t k ) and a pulse width (T on ).

4. The system of claim 3 , wherein T on is less than or equal to the pulse period (C).

5. The system of claim 2 , wherein n is a positive integer and τ a is a stroke time corresponding to an actuator, and wherein C is equal to nτ a .

6. The system of claim 5 , wherein n is equal to ten.

7. The system of claim 1 , wherein the controller comprises a position detector configured to determine a position of the valve (x i ).

8. The system of claim 7 , wherein the controller is configured to determine a pulse width (T on ) of the PWM signal, wherein the pulse width (T on ) is equal to

x
i

x
min

⁢
C

and C is a pulse period.

9. The system of claim 1 , wherein the controller comprises a position detector configured to determine a position of the valve (x i ), and
in response to a determination that the measured flow rate is not equal to the predetermined flow rate value, the controller is configured to:
set {circumflex over (x)} min equal to a minimum value of {circumflex over (x)} min and x i ;
set x min equal to {circumflex over (x)} min ; and

in response to a determination that the measured flow rate is equal to the predetermined flow rate value, the controller is configured to:
set {circumflex over (x)} min equal to a maximum value of {circumflex over (x)} min and x i ; and
set x min equal to {circumflex over (x)} min .

10. A system for monitoring and controlling flow rate of a fluid through a valve, the system comprising:
a valve configured to regulate a flow of a fluid through a conduit;
an actuator coupled to the valve and configured to drive the valve between multiple positions;
a flow rate sensor configured to measure the flow rate of the fluid through the valve; and
a controller in communication with the actuator and the flow rate sensor and configured to:
receive the measured flow rate;
determine if the measured flow rate is equal to zero;
in response to a determination that the measured flow rate is equal to zero:
determine a minimum valve position threshold (x min );
determine a minimum flow rate threshold (y min ) using x min ;
generate a pulse-width modulated (PWM) signal that switches between zero and y min ;
calculate a corrected flow rate (ŷ f ) using the PWM signal;
control a valve operation using the corrected flow rate; and

in response to a determination that the measured flow rate is greater than zero:
control the valve operation using the measured flow rate.

11. The system of claim 10 , wherein the controller is further configured to:
determine if t k <t r ≤(t k +T on ) where t k is a beginning of a pulse period, t r is a run time, and T on is a pulse width;
determine if (t k +T on )<t r ≤(t k +C) where C is a pulse period;
in response to a determination that t k <t r ≤(t k +T on ):
set the PWM signal equal to y min ; and

in response to a determination that (t k +T on )<t r ≤(t k +C):
set the PWM signal equal to zero.

12. The system of claim 11 , wherein n is a positive integer and τ a is a stroke time corresponding to the actuator, and wherein C is equal to nτ a .

13. The system of claim 10 , wherein the controller comprises a position detector configured to determine a position of the valve (x i ).

14. The system of claim 13 , wherein a pulse width (T on ) is equal to

x
i

x
min

⁢
C

and C is a pulse period.

15. The system of claim 10 , wherein, in response to a determination that the measured flow rate is not equal to 0, the controller is configured to:
set {circumflex over (x)} min equal to a minimum value of {circumflex over (x)} min and x i ;
set x min equal to {circumflex over (x)} min ; and
in response to a determination that the measured flow rate is equal to 0, the controller is configured to:
set {circumflex over (x)} min equal to a maximum value of {circumflex over (x)} min and x i ; and
set x min equal to {circumflex over (x)} min .

16. A method for monitoring and controlling flow rate of a fluid through a valve, the method comprising:
measuring the flow rate;
determining if the flow rate is equal to zero; and
in response to a determination that the flow rate is equal to zero:
determining a valve opening position (x i );
determining a minimum valve position threshold (x min );
determining a minimum flow rate threshold (y min ) corresponding to x min ;
calculating a corrected flow rate (ŷ f ) using a pulse-width modulated (PWM) signal, wherein the PWM signal is configured to switch between zero and y min ; and
controlling a valve operation using the corrected flow rate (ŷ f ).

17. The method of claim 16 further comprising:
in response to a determination that the flow rate is not equal to zero:
determining an estimated minimum valve position threshold ({circumflex over (x)} min ); and
setting {circumflex over (x)} min equal to a minimum value of {circumflex over (x)} min and x i ;

in response to a determination that the flow rate is equal to zero:
determining the estimated minimum valve position threshold ({circumflex over (x)} min ); and
setting {circumflex over (x)} min equal to a maximum value of {circumflex over (x)} min and x i ;

initializing a filtered estimate ( x min ) to {circumflex over (x)} min ;
filtering {circumflex over (x)} min using a filtering equation comprising

x
_

min

=

Assignees

• Johnson Controls Tech Co

Inventors

• Alcala Perez Carlos Felipe
• Drees Kirk H
• Salsbury Timothy I

Classifications

• F24F2140/40

  Damper positions, e.g. open or closed · CPC title

• G01F25/00

  Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume · CPC title

• G01F15/068

  with electrical means (G01F15/063 takes precedence) · CPC title

• G01F15/066

  involving magnetic transmission devices · CPC title

• G01F1/363

  with electrical or electro-mechanical indication (G01F1/37 and G01F1/38 take precedence) · CPC title