Feature set and methods for a digital positioner

Patent metadata

Field	Value
Publication number	US-11368120-B2
Application number	US-202016881798-A
Country	US
Kind code	B2
Filing date	May 22, 2020
Priority date	May 22, 2020
Publication date	Jun 21, 2022
Grant date	Jun 21, 2022

Abstract

A digital positioner for a valve includes a valve controller configured to obtain a set point value for a valve travel of a valve, and generate a pulse-width modulated current signal based on the set point value. The digital positioner also includes a current-to-pressure converter configured to receive the pulse-width modulated current signal from the valve controller, convert the pulse-width modulated current signal to a pulse-width modulated pressure signal, and provide the pulse-width modulated pressure signal to a pneumatic actuator in the valve to adjust a position of the valve.

First claim

What is claimed is:

1. A valve controller comprising:
one or more processors; and
a non-transitory computer-readable memory coupled to the one or more processors, and storing thereon instructions that, when executed by the one or more processors, cause the valve controller to:
obtain a set point value for a valve travel of a valve or an amount of pressure at the valve;
obtain a threshold dead band value for the valve travel or the amount of pressure;
adjust the threshold dead band value based on changes in valve travel values or changes in pressure values over time;
generate a drive signal based on the set point value and the adjusted threshold dead band value;
generate a pulse-width modulated current signal in accordance with the drive signal; and
provide the pulse-width modulated current signal to a current-to-pressure converter that converts the pulse-width modulated current signal to a pulse-width modulated pressure signal and provides the pulse-width modulated pressure signal to a pneumatic actuator in the valve to adjust a position of the valve.

2. The valve controller of claim 1 , wherein to adjust the threshold dead band value based on changes in valve travel values or changes in pressure values over time, the instructions cause the valve controller to:
compare a difference between the set point value and a current valve travel or valve pressure value to the threshold dead band value;
determine that the current valve travel or valve pressure value is within a dead band region of the set point value when the difference between the set point value and the current valve travel or valve pressure value is less than the threshold dead band value; and
in response to determining that the current valve travel or valve pressure value is within the dead band region, adjust the threshold dead band value over time based on a difference between a subsequent valve travel or valve pressure value and the current valve travel or valve pressure value.

3. The valve controller of claim 2 , wherein to adjust the threshold dead band value over time, the instructions cause the valve controller to:
increase the threshold dead band value in response to determining that the subsequent valve travel or valve pressure value exceeds a sum of the set point value and the threshold dead band value.

4. The valve controller of claim 2 , wherein to adjust the threshold dead band value over time, the instructions cause the valve controller to:
compare the difference between the set point value and the subsequent valve travel or valve pressure value to the threshold dead band value; and
in response to determining that the difference between the set point value and the subsequent valve travel or valve pressure value is more than half of the threshold dead band value, decrease the threshold dead band value.

5. The valve controller of claim 2 , wherein the instructions cause the valve controller to:
obtain a plurality of subsequent valve travel or valve pressure values after threshold periods of time;
for each of the plurality of subsequent valve travel or valve pressure values, increase a counter in response to determining that a difference between the set point value and subsequent valve travel or valve pressure value is more than half of the threshold dead band value; and
decrease the threshold dead band value in response to determining that the counter exceeds a threshold number.

6. A digital positioner for a valve comprising:
a valve controller including:
one or more processors; and
a non-transitory computer-readable memory coupled to the one or more processors and storing instructions thereon that, when executed by the one or more processors, cause the valve controller to:
obtain a set point value for a valve travel of a valve or an amount of pressure at the valve;
compare the set point value to a maximum threshold value or a minimum threshold value;
in response to determining that the set point value exceeds the maximum threshold value or is less than the minimum threshold value, generate a drive signal corresponding to the maximum threshold value or the minimum threshold value;
set a saturation flag indicating that the drive signal saturated to the maximum threshold value or the minimum threshold value; and
generate a pulse-width modulated current signal in accordance with the drive signal; and

a current-to-pressure converter configured to receive the pulse-width modulated current signal from the valve controller, convert the pulse-width modulated current signal to a pulse-width modulated pressure signal, and provide the pulse-width modulated pressure signal to a pneumatic actuator in the valve to adjust a position of the valve.

7. The digital positioner of claim 6 , wherein the instructions cause the valve controller to:
compare the set point value to the maximum threshold value; and
in response to determining that the set point value exceeds the maximum threshold value:
generate the drive signal corresponding to the maximum threshold value; and
set the saturation flag indicating that the drive signal saturated to the maximum threshold value.

8. The digital positioner of claim 7 , wherein the instructions cause the valve controller to:
obtain a new set point value;
in a first instance, in response to determining that the saturation flag has been set indicating that the drive signal saturated to the maximum threshold value:
compare the new set point value to a threshold amount below the maximum threshold value; and
in response to determining that the new set point value is less than the threshold amount below the maximum threshold value, reset the saturation flag, and generate a drive signal corresponding to the new set point value; and

in a second instance, in response to determining that the saturation flag has not been set, compare the new set point value to the maximum threshold value to determine the drive signal to generate.

9. The digital positioner of claim 6 , wherein the instructions cause the valve controller to:
compare the set point value to the minimum threshold value; and
in response to determining that the set point value is less than the minimum threshold value:
generate the drive signal corresponding to the minimum threshold value; and
set the saturation flag indicating that the drive signal saturated to the minimum threshold value.

10. The digital positioner of claim 9 , wherein the instructions cause the valve controller to:
obtain a new set point value;
in a first instance, in response to determining that the saturation flag has been set indicating that the pulse-width modulated current signal saturated to the minimum threshold value:
compare the new set point value to a threshold amount above the minimum threshold value; and
in response to determining that the new set point value is more than the threshold amount above the minimum threshold value, reset the saturation flag, and generate a drive signal corresponding to the new set point value; and

in a second instance, in response to determining that the saturation flag has not been set, compare the new set point value to the minimum threshold value to determine the drive signal to generate.

11. The digital positioner of claim 6 , wherein the instructions cause the valve controller to generate a first pulse-width modulated current signal and a second pulse-width modulated current signal, wherein the current-to-pressure converter includes a first current-to-pressure converter configured to receive the first pulse-width modulated current signal and convert the first pulse-width modulated current signal to a first pulse-width modulated pressure signal, and a second current-to-pressure

Assignees

• Fisher Controls Int Llc

Inventors

• Gassman George W

Classifications

• G05B19/46

  hydraulic · CPC title

• F16K37/0083

  by measuring valve parameters · CPC title

• F15B21/087

  Control strategy, e.g. with block diagram · CPC title

• F04B53/108

  Valves characterised by the material · CPC title

• H02P29/032

  Preventing damage to the motor, e.g. setting individual current limits for different drive conditions · CPC title