Diagnostic device and method for pressure regulator

• US 6,035,878 A
• Filed: 09/22/1997
• Issued: 03/14/2000
• Est. Priority Date: 09/22/1997
• Status: Expired due to Term

• Current Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Original Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Inventors: Roper, Daniel G., Adams, Paul R., Gabel, Karl J.
• Primary Examiner(s): Hepperle, Stephen M.
• Application Number:
  US08/935,176
• Time in Patent Office: 904 Days
• Field of Search: 137/487.5, 137/492.5, 137/505.41, 137/1, 137/12, 137/489.5, 137/557
• US Class Current: 137/1
• CPC Class Codes: G05D 16/2095 using membranes within the main valve
• CPC Class Codes: Y10T 137/0318 Processes
• CPC Class Codes: Y10T 137/0379 By fluid pressure
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve
• CPC Class Codes: Y10T 137/7768 Pilot controls supply to pressure chamber
• CPC Class Codes: Y10T 137/8326 Fluid pressure responsive indicator, recorder or alarm

Abstract

A diagnostic device and method for an intelligent pressure regulator which maintains a fluid in a process at a predetermined pressure. The regulator includes an electronic controller which enhances regulator performance and provides self-diagnostics and communications capabilities. The electronic controller includes a pressure sensor which provides a signal indicating the pressure of the fluid being controlled, an adjusting pressure for adjusting the position of a throttling element; and a PID controller which receives the signal indicating the pressure of the fluid being controlled and applies the adjusting pressure to the actuator in response to the signal.

Claims

1. A pressure regulator for maintaining a fluid in a process at a predetermined pressure comprising:

a body defining a fluid inlet, a fluid outlet, and a fluid flow passage in fluid connection with the inlet and the outlet;

a throttling element moveable within the flow passage for selectively restricting fluid flow through the flow passage;

an actuator coupled to the throttling element for selectively moving the throttling element, the actuator having a control side and a reference side;

a reference load coupled to the reference side of the actuator for biasing the throttling element to a predetermined reference position;

a feedback line for applying pressure from the fluid in the process to the control side of the actuator for moving the actuator against the reference load to position the throttling element within the flow passage;

a first pressure sensor which provides a signal indicating the pressure of the fluid in the process at a first point in the process; and

a controller which receives the signal indicating the pressure of the fluid and outputs an error signal corresponding to the difference between the sensed pressure and a predetermined pressure level, the controller including a digital memory for storing the error signals at different times during the operation of the pressure regulator, and a processor for running a routine that compares the error signals at different times to obtain diagnostic data corresponding to the operation of the pressure regulator.

2. The pressure regulator of claim 1 wherein the controller digital memory includes baseline data corresponding to a baseline operating characteristic of the pressure regulator.

3. The pressure regulator of claim 2 further comprising an alarm device coupled to the controller, wherein the controller is adapted to compare the diagnostic data and the baseline data and actuate the alarm device whenever the comparison indicates that the diagnostic data has deviated from the baseline data by a predetermined amount.

4. The pressure regulator of claim 1 further comprising a second pressure sensor for sensing the pressure of the fluid at a second point in the process, wherein the controller is adapted to calculate, at various points in time, regulator offset values that correspond to the difference between the pressure detected by the first sensor and the pressure detected by the second sensor, and wherein the controller is adapted to store digital representations of the calculated regulator offset values in the controller memory.

5. The pressure regulator of claim 4 wherein the first pressure sensor is adapted to detect the fluid pressure at the inlet and the second pressure sensor is adapted to detect the fluid pressure at the outlet, and wherein the processor is adapted to run a routine that determines and stores in the controller memory, regulator offset values for a plurality of different inlet pressures.

6. The pressure regulator of claim 1 further comprising a sensor for detecting the direction of movement of the throttling element, wherein the processor is adapted to generate diagnostic data concerning the hysteric error of the pressure regulator by:

(i) storing in the controller memory a first digital signal reflecting the pressure detected by the first pressure sensor when the throttling element is moving in a first direction;

(ii) storing in the controller memory a second digital signal reflecting the pressure detected by the first pressure sensor when the throttling element is moving in a second direction, opposite to the first direction; and

(iii) comparing the first and second digital signals to produce a difference signal that is reflective of the hysteretic error of the pressure regulator.

7. The pressure regulator of claim 1 wherein the controller memory includes a baseline datum reflective of a predetermined fluid pressure at which the throttling element will move to a completely closed position and wherein the processor is adapted to:

(i) store in controller memory a digital signal corresponding to the fluid pressure detected by the first pressure sensor at which the throttling element moves to a completely closed position; and

(ii) compare the baseline datum with the digital signal corresponding to the fluid pressure detected by he first pressure sensor at which the throttling element moves to a completely closed position to generate a diagnostic signal corresponding to the difference between the compared signals.

8. A device for sensing cavatation and flashing in a pressure regulator that uses the pressure of a fluid in the process to position a throttling element to restrict fluid flow through the pressure regulator, the pressure regulator including an inlet, the device comprising:

an inlet pressure sensor;

a processor including a memory having a cavitation/flashing index, a critical pressure ratio constant, and input constants of the fluid stream vapor pressure stored therein;

the processor including a routine for calculating absolute pressure drop (Δ

P_A) according to Δ

P_A =K_c (P₁ -r_c P_v) where K_c =the cavitation/flashing index, P₁ =sensed inlet pressure, r_c =the critical pressure ratio constant and P_v =vapor pressure; and

the processor further including a routine for comparing Δ

P_A to the input constants of the fluid stream vapor pressure to detect flashing and cavitation.

9. A device for sensing cavatation in a pressure regulator that uses the pressure of a fluid in the process to position a throttling element within a flow passage to restrict fluid flow through the pressure regulator, the device comprising:

a sensor adapted to detect at least one physical parameter associated with the pressure regulator and provide electrical signals corresponding to the detected physical parameter, wherein the physical parameter is subject to change upon the onset and presence of cavitation,

a memory having a first set of electrical baseline physical parameter signals stored therein, the first set of baseline physical parameter signals corresponding to the physical parameter characteristics associated with at least one stage of flashing; and

a processor adapted to receive from the sensor the electrical signals corresponding to the detected physical parameter and to receive form the memory the baseline physical parameter signals and to compare the identified signals and provide an electrical signal reflecting the occurrence of flashing whenever there is an approximate match of the signals.

10. The device of claim 9 wherein the sensor is an acoustic sensor coupled to the flow passage for sensing acoustic noise characteristics within the flow passage and wherein the the first set of baseline physical parameter signals correspond to the noise characteristics associated with various stages of flashing.

11. The device of claim 9 wherein the sensor is a seismic sensor coupled to the flow passage for sensing vibration characteristics within the flow passage and wherein the first set of baseline physical parameter signals correspond to the vibration characteristics associated with various stages of flashing.

12. The device of claim 9 wherein the a memory has a second set of electrical baseline physical parameter signals stored therein, the second set of baseline physical parameter signals corresponding to the physical parameter characteristics associated with at least one stage of cavitation;

and wherein the processor is adapted to receive from the sensor the electrical signals corresponding to the detected physical parameter and to receive form the memory the second set of baseline physical parameter signals and to compare the identified signals and provide an electrical signal reflecting the occurrence of cavitation whenever there is an approximate match of the signals.

13. A method for performing on-line diagnostics on a pressure regulator which maintains pressure in a process at a set point value by applying the process pressure to an actuator to adjust a fluid flow throttling element, the method comprising the acts of:

collecting baseline performance data for the regulator, reflecting the operating characteristics of the pressure regulator under a given set of operating conditions and storing the baseline performance data in a memory device;

temporarily introducing a step change to the set point to change the set point to an adjusted set point value;

collecting performance data reflecting the operating characteristics of the regulator as it brings the process pressure towards the adjusted set point value;

comparing the performance data to the baseline data to obtain diagnostic information concerning the operation of the pressure regulator.

14. The method of claim 13 wherein:

(i) the act of collecting baseline performance data includes the acts of sensing the pressure of the process and determining a baseline offset value corresponding to the difference between the sensed pressure and a predetermined desired pressure;

(ii) the act of collecting performance data includes the acts of sensing the pressure of the process and determining a performance offset value corresponding to the difference between the sensed pressure and the predetermined desired pressure; and

(iii) the act of comparing the performance data to the baseline data includes the act of comparing the baseline offset value to the performance offset value.

15. The method of claim 13 wherein the act of collecting baseline performance data includes the act of determining the process pressure at which the throttling element moves to a position which completely prevents fluid flow.

16. The method of claim 15 wherein the wherein the act of collecting performance data includes the act of determining the process pressure at which the throttling element moves to a position which completely prevents fluid flow.

17. The method of claim 13 wherein the actuator includes a reference side and a control side, and wherein the act of collecting baseline performance data and the act of determining performance data each comprise determining a first force exerted on the reference side;

determining a second force exerted on the control side; and

comparing the first and second forces to identify actuator malfunctions.

18. A method for determining the inlet pressure sensitivity of a pressure regulator which maintains pressure in a process at a set point value by applying the process pressure to an actuator to adjust a fluid flow throttling element, the pressure regulator having an inlet, the method comprising the acts of:

detecting the pressure at the regulator inlet for a given fluid flow at a first point in time and storing in a digital memory a representation of the given fluid flow and the pressure detected at the first point in time;

monitoring the pressure at the regulator inlet over time to identify a second point in time where the pressure at the second point in time is different than the pressure detected at the first point in time;

storing in a digital memory a representation of the given fluid flow and the pressure detected at the second point in time;

comparing the representation of the given fluid flow and the pressure detected at the first point in time with the representation of the given fluid flow and the pressure detected at the second point in time to provide a difference signal indicative of the inlet pressure sensitivity.

19. A method for determining the hysteretic error of a pressure regulator which maintains pressure in a process at a set point value by applying the process pressure to an actuator to adjust a fluid flow throttling element, the pressure regulator having an inlet, the method comprising the acts of:

detecting the flow rate of the fluid passing through the regulator;

identifying a first point in time where the flow rate through the regulator is a first flow rate;

identifying a second point in time following the first point in time, where the flow rate through the regulator is a second flow rate, wherein the second flow rate is less than the first flow rate, and storing in a digital memory a representation of the pressure of the process at the second point in time;

identifying a third point in time where the flow rate through the regulator is a third flow rate;

identifying a fourth point in time following the third point in time, where the flow rate through the regulator is a third flow rate, wherein the third flow rate is greater than the third flow rate, and storing in a digital memory a representation of the pressure of the process at the fourth point in time; and

comparing the representation of the pressure at the second point in time with the representation of the pressure at the fourth point in time to calculate a dead band value for diagnosing the regulator.

20. The method of claim 19 wherein the third point in time follows the second point in time.