Valve positioner system

• US 20010037670A1
• Filed: 04/10/2001
• Published: 11/08/2001
• Est. Priority Date: 07/23/1997
• Status: Active Grant

• Current Assignee: Dresser Incorporated (Nagano Keiki Company Limited)
• Original Assignee: Dresser Incorporated (Nagano Keiki Company Limited)
• Inventors: Villier, Raymond, Schoonover, Larry, Levesque, Peter, Colwell, Christopher, Stares, James, Boger, Henry, Vital, Denis, Zhou, Chunhe
• Granted Patent: US 6,453,261 B2
• Time in Patent Office: Days
• US Class Current: 73/1.72
• CPC Class Codes: F15B 19/005 Fault detection or monitoring
• CPC Class Codes: F15B 21/087 Control strategy, e.g. with block diagram
• CPC Class Codes: F15B 5/006 with electrical means, e.g. electropneumatic transducer F15B5/003 takes precedence
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 19/44 pneumatic
• CPC Class Codes: G05B 2219/25252 Microprocessor
• CPC Class Codes: G05B 2219/41032 Backlash
• CPC Class Codes: G05B 2219/41143 Compensation of dynamic characteristic of actuator
• CPC Class Codes: G05B 2219/41154 Friction, compensation for friction
• CPC Class Codes: G05B 2219/41304 Pneumatic
• CPC Class Codes: G05B 2219/41311 Pilot valve with feedback of position
• CPC Class Codes: G05B 5/01 electric
• CPC Class Codes: G05B 7/02 electric

Abstract

A valve positioner system that includes one or more unique control methods and devices, including several routines to facilitate the continuous maintenance, calibration and adjustment requirements of the valve. The positioner system may utilize pressure and position feedback signals to monitor the valve. The positioner system may utilize an external controller for various diagnostic and other routines. The positioner system can provide automatic positioning and can operate in a manual operating mode or an automatic operating mode. The positioner system can diagnose the valve while the valve process is running or during a maintenance operation. The positioner system can provide nonlinear control of the valve position. The positioner system can self-tune and self-characterize the valve to assure uniform position control. The positioner system can provide valve control through pressure feedback when a position feedback fails or other diagnosed problems. The positioner system can provide constraints to prevent slope reversal or slope changes in the valve characterization that would produce undesirable valve gain.

Claims

1. A method for detecting limit cycling in a valve, the method comprising:

measuring a plurality of positions of the valve;

measuring a plurality of actuator pressures for the valve;

determining zero crossings for the position and pressure measurements;

determining a phase relationship from the zero crossings;

comparing the phase relationship to a predetermined value; and

detecting limit cycling only if the phase relationship exceeds the predetermined value by a predetermined amount.

2. A method according to

claim 1

wherein the predetermined amount is less than 90°

.

3. A method according to

claim 1

further comprising:

notifying a user of the limit cycling only if limit cycling is detected.

4. A method for detecting limit cycling in a valve, the method comprising the steps of:

measuring a lag associated with the valve;

measuring a period for the valve;

determining a ratio of lag vs. period;

comparing the ratio to a predetermined value; and

if the ratio is greater than the predetermined value, reporting limit cycling.

5. The method of

claim 4

further comprising:

if the ratio is less than the predetermined value, reporting loop tuning.

6. The method of

claim 4

further comprising:

determining a pressure associated with the valve; and

determining a position for the valve;

wherein the lag and period are determined from the determined pressure and position.

7. The method of

claim 6

wherein pressure is for an actuator of the valve and is an average of a plurality of sampled values.

8. A positioner capable of detecting limit cycling in a valve, the positioner comprising:

means for measuring a plurality of actuator pressures for the valve;

means for measuring a plurality of positions of the valve;

means for determining zero crossings for the position and pressure measurements;

means for determining a phase relationship from the zero crossings;

means for comparing the phase relationship to a predetermined value; and

means for determining limit cycling in the valve only if the phase relationship exceeds predetermined value by a predetermined amount.

9. A positioner according to

claim 8

wherein the predetermined amount is less than 90°

.

10. A positioner according to

claim 8

further comprising:

means for notifying a user of the limit cycling responsive to limit cycling being determined.

11. A system for detecting limit cycling in a valve, comprising:

means for measuring a lag associated with the valve;

means for measuring a period for the valve;

means for determining a ratio of lag vs. period;

means for comparing the ratio to a predetermined value; and

means for reporting limit cycling if the ratio is greater than the predetermined value.

12. The system of

claim 11

wherein the means for reporting also reports loop tuning if the ratio is less than the predetermined value.

13. The system of

claim 11

further comprising:

means for determining a pressure associated with the valve; and

means for determining a position for the valve;

wherein the lag and period are determined from the determined pressure and position.

14. The system of

claim 13

wherein pressure is for an actuator of the valve and is an average of a plurality of sampled values.

15. For an electronically controllable valve, method for bumpless transfer from a manual mode of operation to an automatic mode of operation, the method comprising:

determining when the automatic mode has been selected;

receiving a position signal from the automatic mode for a new position;

receiving a valve position from the valve;

comparing the new position to the valve position;

if the new position is within a predefined limit of the valve position, allowing the valve to enter automatic mode; and

if the new position is outside of the predefined limit from the valve position, performing the steps of;

i) holding the valve in a current position;

ii) informing a user of the discrepancy in positions;

iii) instructing the user to manually adjust the valve closer to the new position.

16. The method of

claim 15

wherein the user is informed and instructed through a display associated with the valve.

17. The method of

claim 15

further comprising:

iv) receiving a second position signal that indicates a second new position for the valve;

v) comparing the second new position to the valve position;

vi) if the second new position is within a predefined limit of the valve position, allowing the valve to enter automatic mode.

18. The method of

claim 15

wherein the new position is characterized before it is compared with the valve position.

19. A positioner for an electronically controllable valve capable of providing bumpless transfer from a manual mode of operation to an automatic mode of operation, the positioner comprising:

means for determining when the automatic mode has been selected;

means for receiving a position signal from the automatic mode for a new position;

means for receiving a valve position from the valve;

means for comparing the new position to the valve position;

means for allowing the valve to enter automatic mode if the new position is within a predefined limit of the valve position; and

means for informing a user of the discrepancy in positions if the new position is outside of the predefined limit from the valve position.

20. The positioner of

claim 19

further comprising:

means for instructing the user to manually adjust the valve closer to the new position if the new position is outside of the predefined limit from the valve position.

21. The positioner of

claim 20

wherein the user is informed and instructed through a display associated with the valve.

22. The positioner of

claim 19

wherein:

the means for receiving can also receive a second position signal that indicates a second new position for the valve if the new position was outside of the predefined limit from the valve position;

the means for comparing can also compare the second new position to the valve position; and

the means for allowing can also allow the valve to enter automatic mode if the second new position is within a predefined limit of the valve position.

23. The positioner of

claim 19

wherein the new position is characterized before it is compared with the valve position.

25. The method of

claim 23

further comprising:

if the valve is near an end of travel, suspending the repeated averaging.

26. The method of

claim 23

further comprising:

saving the average for later retrieval by the positioner.

28. The method of

claim 26

further comprising:

determining if the valve is nearly fully open or fully closed;

if the valve is nearly fully open or fully closed;

preventing the updating of the BIAS.

29. The method of

claim 26

further comprising:

determining if a position error exists in the valve;

if a position error exists;

preventing the updating of the BIAS.

24. A control method for use by a valve positioner, the method comprising:

allowing the valve to move in a first direction;

repeatedly calculating a BIAS value for the positioner;

repeatedly averaging the BIAS value over a period of time;

comparing a current BIAS value to the average,

if the current BIAS value differs significantly from the average BIAS value, stopping the repeated averaging; and

if the positioner tries to move the valve in a second direction, replacing the current BIAS value with the average BIAS value.

27. A method for adjusting a BIAS for a spool valve in an automatically positionable valve, the method comprising:

maintaining an average of the BIAS over a period of time;

measuring a first value for BIAS;

updating the BIAS for the spool valve with the first value;

measuring a second value for BIAS after measuring the first value; and

updating the BIAS for the spool valve with the second value;

wherein, if the second value of BIAS is between the first value and the average, the BIAS is updated quickly towards the average and if the second value of BIAS is not between the first value and the average, the BIAS is updated slowly towards the average.

30. A valve positioner comprising:

an output signaling device for sending output signals;

a control device for controlling a valve responsive to the output signals;

means for repeatedly averaging the output signals over a period of time as the valve moves in a first direction;

means for comparing a new output signal from the output signaling device to the average; and

means for replacing the new output signal with the average if the positioner tries to move the valve in a second direction;

wherein the averaging means stops averaging if the new output signal differs significantly from the average.

31. The positioner of

claim 30

further comprising:

if the valve is near an end of travel, suspending the repeated averaging.

32. A positioner for an automatically positionable valve comprising:

a spool valve for controlling an actuator, the spool valve being responsive to a BIAS output;

means for consecutively calculating first and second BIAS values;

means for maintaining an average of at least the first and second BIAS values;

means for consecutively calculating third and fourth BIAS values;

means for determining the BIAS output from the BIAS values; and

means for adjusting the BIAS output towards the average if the fourth BIAS value is between the third BIAS value and the average.

33. The positioner of

claim 32

further comprising:

means for determining if the valve is nearly fully open or fully closed; and

means for preventing the adjustment of the BIAS output if the valve is nearly fully open or fully closed.

34. The positioner of

claim 32

further comprising:

means for determining if a position error exists in the valve; and

wherein the preventing means is also responsive to whether a position error exists.

35. A method for measuring a valve signature for a valve having an actuator, the method comprising:

opening a spool valve of the actuator to increase actuator pressure;

measuring a plurality of pressure data for the actuator and position data for the valve as the valve is opening;

closing the spool valve to decrease the actuator pressure;

measuring a plurality of pressure data for the actuator and position data for the valve as the valve is closing;

analyzing the measured data to determine friction and hysteresis for the valve; and

determining the valve signature from the analyzed data.

36. The method of

claim 35

further comprising:

storing the pressure data during the measuring steps.

37. The method of

claim 35

wherein the valve provides position feedback signals from which the position data is measured.

38. The method of

claim 35

being performed by a positioner operating in a diagnostic mode.

39. The method of

claim 35

being performed by a positioner operating in a normal operation mode.

40. The method of

claim 35

wherein the valve has a range of operation and the spool valve is opened and closed for a limited period of time so that the valve only moves through a portion of the range of operation.

41. A method for diagnosing a valve having position feedback capabilities and controlled through an actuator, the method comprising:

positioning the valve at a first location;

sampling a position of the valve at the first location;

adjusting a fluid supply to the actuator to move the valve to a second location;

sampling a position of the valve at the second location; and

determining a first valve signature from the sampled positions.

42. The method of

claim 41

further comprising:

adjusting the fluid supply to the actuator to move the valve to a third location, wherein the valve moves in an opposite direction than when the valve was moved to the second location;

sampling a position of the valve at the third location; and

determining a second valve signature from the sampled second and third positions.

43. The method of

claim 42

wherein the fluid supply to the actuator is adjusted by manipulating a spool valve.

44. The method of

claim 42

further comprising:

calculating a range for the actuator from the sampled positions;

calculating friction for each position by analyzing the fluid supply and sampled positions.

45. The method of

claim 43

further comprising:

finding a value for the spool valve to identify a configuration that does not adjust the fluid supply to the actuator.

46. A positioner for controlling a valve with an actuator and capable of determining a valve signature, the positioner comprising:

a spool valve connected to the actuator;

a pressure feedback for reporting actuator pressure;

a position feedback for reporting valve position;

means for opening the spool valve to increase the actuator pressure;

means for measuring a plurality of actuator pressures and valve positions as the valve is opening;

means for closing the spool valve to decrease the actuator pressure;

means for measuring a plurality of actuator pressures and valve positions as the valve is closing;

means for analyzing the measured data to determine a friction measurement and hysteresis value for the valve; and

means for calculating the valve signature from the friction measurement and hysteresis value.

47. The positioner of

claim 46

further comprising:

memory for storing the pressure data during the measuring steps.

48. The positioner of

claim 46

wherein the valve has a range of operation and the spool valve is opened and closed for a limited period of time so that the valve only moves through a portion of the range of operation.

49. A system for diagnosing a valve having position feedback capabilities and controlled through an actuator, the system comprising:

a spool valve for supplying a fluid to the actuator;

means for positioning the valve at a first location using the position feedback capabilities;

means for sampling a position of the valve at the first location and for sampling a position of the valve after the fluid supply has been adjusted in the first direction

means for adjusting the fluid supply in a first direction; and

means for determining a first valve signature from the sampled positions for diagnosing the valve.

50. The system of

claim 49

further comprising:

means for adjusting the fluid supply in a direction opposite the first direction;

the sampling also for sampling a position of the valve after the fluid supply has been adjusted in the opposite direction; and

the determining means also determining a second valve signature from the sampled second and third positions for diagnosing the valve.

51. The system of

claim 50

further comprising:

means for calculating a range for the actuator from the sampled positions; and

means for calculating friction for each position by analyzing the fluid supply and sampled positions;

wherein the valve is further diagnosed by the range and the friction.

52. The system of

claim 51

further comprising:

means for finding a value for the spool valve to identify a configuration that does not adjust the fluid supply to the actuator.

53. A method for performing diagnostics on a valve having an actuator, the method comprising:

positioning the valve at a first end of a test range of valve positions;

incrementing fluid pressure to the actuator until it reaches a second end of the test range;

decrementing fluid pressure to the actuator until it reaches the first end of the test range;

sampling valve position and actuator pressure data during the incrementing and decrementing;

storing the sampled position and pressure data in memory; and

analyzing the stored data.

54. The method of

claim 53

wherein the test range is relatively small, as compared to a full range of movement of the valve.

55. The method of

claim 54

wherein the valve is operating in a normal operation mode.

56. A system for performing diagnostics on a valve having an actuator, comprising:

means for positioning the valve at a first end of a test range of valve positions;

means for incrementing a fluid pressure to the actuator until it reaches a second end of the test range and decrementing the fluid pressure to the actuator until it reaches the first end of the test range;

means for sampling valve position and actuator pressure data as the fluid pressure is incrementing and decrementing;

memory for storing the sampled position and pressure data; and

means for analyzing the stored data.

57. The system of

claim 56

wherein the test range is relatively small, as compared to a full range of movement of the valve.

58. The system of

claim 57

wherein the valve is operating in a normal operation mode.

59. A method for providing valve response feedback to a user, the method comprising:

defining a characterization function for the valve;

receiving a position set point for the valve;

receiving an actual valve position from the valve;

displaying the actual valve position on a graph; and

displaying a characterization of the position set point on the Graph;

wherein if the valve is operating correctly, the actual valve position and the characterization of the set point will align on the graph.

60. The method of

claim 59

wherein the characterization function of the valve is not an equal-percentage type.

61. A method for providing valve response feedback to a user, the method comprising:

defining a characterization function for the valve;

determining an inverse function of the characterization function;

receiving a position set point for the valve;

receiving an actual valve position from the valve;

determining a predicted set point from the actual valve position and the inverse function;

displaying the predicted set point on a graph; and

displaying the position set point on the graph;

wherein if the valve is operating correctly, the predicted set point and the position set point will align on the graph.

62. The method of

claim 61

wherein the characterization function of the valve is not an equal-percentage type.

63. A system for providing valve response feedback to a user, comprising:

means for performing a characterization function for a valve;

means for receiving a position set point for the valve;

means for receiving an actual valve position from the valve; and

a display for showing the actual valve position and a characterization of the position set point on a single graph;

wherein if the valve is operating correctly, the actual valve position and the characterization of the set point will align on the graph.

64. The system of

claim 63

wherein the characterization function of the valve is not an equal-percentage type.

65. A system for providing valve response feedback to a user, comprising:

means for performing an inverse characterization function for a valve;

means for receiving a position set point for the valve;

means for receiving an actual valve position of the valve;

means for determining a predicted set point from the actual valve position and the inverse characterization function; and

a display for showing the predicted set point and the position set point on a single graph;

wherein if the valve is operating correctly, the predicted set point and the position set point will align on the graph.

66. The system of

claim 65

wherein a characterization function of the valve is not an equal-percentage type.

67. A method for providing automatic compensation for twist of a shaft of a rotary-type valve to a valve positioner, the method comprising:

calibrating the valve positioner while the valve is in a no-force condition;

determining a gradient for the angular displacement of the rotary valve verses positioner signal;

measuring a difference in actuator pressure for a predetermined valve position when the valve is in the no-force condition and when the valve is in a force condition; and

determining a correction function for the valve from the gradient and the difference in actuator pressures.

68. The method of

claim 67

further comprising:

correcting a measured position of the valve in the force condition with the correction function.

69. A positioner for a rotary-type valve, the positioner comprising:

memory for storing a calibration value of the valve while the valve is in a no-force condition and a gradient for describing the angular displacement of the rotary valve verses positioner signal;

means for receiving an actuator pressure from an actuator controlling the valve;

means for receiving a position signal for indicating valve position;

means for measuring a difference in the actuator pressure for a predetermined valve position when the valve is in the no-force condition and when the valve is in a force condition; and

means for determining a correction function for the valve from the gradient and the difference in actuator pressures.

70. The positioner of

claim 69

further comprising:

means for determining an actual position of the valve in the force condition from the correction function and the position signal.

71. A method for providing nonlinear position control to a valve, the method comprising:

calculating a first gain for the valve moving in a first direction;

calculating a second gain for the valve moving in a second direction;

calculating an adjustable gain to compensate for size-related and position-related valve nonlinearities;

receiving a desired position signal for the valve; and

adjusting the desired position by the adjustable gain and either the first or second gain to determine a calculated position signal for the valve.

72. The method of

claim 71

further comprising:

determine a deadzone to accommodate stick/slick behavior of the valve;

determining a damping coefficient to compensate for desired valve responses; and

adjusting the desired position by the deadzone and the damping coefficient to further determine the calculated position signal for the valve.

73. The method of

claim 71

further comprising:

determining a steady state integral control to correct steady-state error; and

adjusting the desired position by the steady state integral control to further determine the calculated position signal for the valve.

74. A positioner for providing nonlinear position control to a valve, comprising:

means for calculating a first gain for the valve moving in a first direction;

means for calculating a second gain for the valve moving in a second direction;

means for calculating an adjustable gain to compensate for size-related and position-related valve nonlinearities;

means for receiving a desired position signal for the valve; and

means for adjusting the desired position by the adjustable gain and either the first or second gain to determine a calculated position signal for the valve.

75. The positioner of

claim 74

further comprising:

means for determine a deadzone to accommodate stick/slick behavior of the valve; and

means for determining a damping coefficient to compensate for desired valve responses;

wherein the adjusting means also adjusts the desired position by the deadzone and the damping coefficient to further determine the calculated position signal for the valve.

76. The positioner of

claim 74

further comprising:

means for determining a steady state integral control to correct steady-state error;

wherein the adjusting means also adjusts the desired position by the steady state integral control to further determine the calculated position signal for the valve.

77. In a pneumatically controllable valve responsive to electronic positioning signals from a current-to-pressure (I/P) transducer, a self-adjusting method for positioning the valve comprising:

finding a BIAS current to the I/P transducer;

performing an open-loop test on the valve by using the found BIAS current for obtaining a system characteristic and a control parameter; and

tuning the control parameter to achieve an improved dynamic response of the valve.

78. The method of

claim 77

wherein the open loop test determines position set points for filling and exhausting operations of an actuator used to control the valve.

79. The method of

claim 77

wherein the open loop test determines a dead time and a dead zone for the valve.

80. The method of

claim 77

wherein the control parameter is tuned by a closed loop test.

81. The method of

claim 80

wherein the closed loop test moves the valve in a single direction and tunes the control parameter with respect to the direction.

82. A self-adjusting positioner for controlling a pneumatically controllable valve responsive to electronic positioning signals from a current-to-pressure (I/P) transducer, the positioner comprising:

means for determining a BIAS current to the I/P transducer;

means for performing an open-loop test on the valve by using the found BIAS current for obtaining a system characteristic and a control parameter; and

means for tuning the control parameter to achieve an improved dynamic response of the valve.

83. The positioner of

claim 82

wherein the open loop test determines position set points for filling and exhausting operations of an actuator used to control the valve.

84. The positioner of

claim 82

wherein the open loop test determines a dead time and a dead zone for the valve.

85. The positioner of

claim 82

wherein the control parameter is tuned by a closed loop test.

86. The positioner of

claim 85

wherein the closed loop test moves the valve in a single direction and tunes the control parameter with respect to the direction.

87. In a controllable valve responsive to positioning signals, a method for characterizing the valve to obtain uniformity of control performance comprising:

providing a cross-reference table to the positioner;

providing a first position signal to move the valve;

measuring at least one process variable from the valve responsive to the first position signal;

storing the process variable in the cross-reference table;

receiving a position set point into a positioner for the valve;

adjusting the position set point by the cross-reference table; and

providing the adjusted position set point as a second positioning signal to the valve.

88. The method of

claim 87

further comprising:

providing a third position signal to move the valve;

measuring at least one process variable from the valve responsive to the third position signal;

storing the process variable in the cross-reference table;

calculating a reverse curve of the first and third position signals from the process variables; and

storing the reverse curve in the cross-reference table to represent the process variables.

89. A system for providing a uniform control performance of a controllable valve responsive to positioning signals, comprising:

a cross-reference table;

means for receiving a first position signal to move the valve;

means for measuring at least one process variable from the valve responsive to the first position signal;

means for storing the process variable in the cross-reference table with the first position;

means for receiving a position set point for the valve;

means for adjusting the position set point by using the cross-reference table; and

means for providing the adjusted position set point as a second positioning signal to the valve.

90. The system of

claim 89

further comprising:

means for receiving a third position signal to move the valve;

the measuring means also measuring at least one process variable from the valve responsive to the third position signal;

the means for storing also storing the process variable in the cross-reference table; and

means for calculating a reverse curve of the first and third position signals from the process variables;

wherein the process variables are stored as the reverse curve in the cross-reference table.

91. In a valve having a pneumatic actuator responsive to position control signals and a position feedback, a method to position the valve comprising:

storing a plurality of pressures corresponding to a plurality of positions in a storage device;

receiving a desired position;

attempting to position the valve by adjusting the actuator until the position feedback matches the desired position;

determining if the valve can be positioned by using the position feedback; and

if the positioning feedback signal fails, choosing one of the stored positions and providing the corresponding actuator pressure for positioning the valve.

92. The method of

claim 91

further comprising:

reading a first actuator pressure for the valve through a pressure sensor;

reading a first position corresponding to the first actuator pressure through the positioning feedback;

reading a second actuator pressure for the valve through the pressure sensor; and

reading a second position corresponding to the second actuator pressure through the positioning feedback;

wherein the first and second positions and actuator pressures are the plurality of positions and pressures stored in the storage device.

93. The method of

claim 92

wherein the first and second positions and actuator pressures are read during normal operation of the valve.

94. The method of

claim 92

wherein the first and second positions and actuator pressures are read during a maintenance operation of the valve.

95. The method of

claim 91

wherein the step of choosing includes reading an actuator pressure and comparing it to the corresponding actuator pressure.

96. The method of

claim 91

further comprising:

converting the desired position to a characterized position;

wherein, the step of choosing includes selecting one of the stored positions that correlates with the characterized position.

97. The method of

claim 91

wherein the step of determining includes

determining an expected pressure corresponding to the characterized position;

and

comparing a pressure feedback to the expected pressure.

98. A positioner for a valve having a pneumatic actuator responsive to position control signals, comprising:

a position feedback connected to the valve for positioning the valve;

memory for storing a plurality of pressures corresponding to a plurality of positions from the position feedback;

means for receiving a desired position;

means for attempting to position the valve by adjusting the actuator until the position feedback matches the desired position;

means for determining if the valve can be positioned by using the position feedback; and

means for choosing one of the stored positions and providing the corresponding actuator pressure for positioning the valve if positioning with the positioning feedback fails.

99. The positioner of

claim 98

further comprising:

a pressure sensor for consecutively reading a first and second actuator pressure for the valve;

wherein the positioning feedback is also for consecutively reading a first and second position corresponding to the first and second actuator pressure; and

wherein the first and second positions and actuator pressures are included with the plurality of positions and pressures stored in the memory.

100. The positioner of

claim 99

wherein the first and second positions and actuator pressures are read during normal operation of the valve.

101. The positioner of

claim 99

wherein the first and second positions and actuator pressures are read during a maintenance operation of the valve.

102. The positioner of

claim 98

wherein the means for choosing reads an actuator pressure and compares the read pressure to the corresponding actuator pressure for positioning the valve.

103. The positioner of

claim 98

further comprising:

means for converting the desired position to a characterized position;

wherein, the means for choosing selects one of the stored positions that correlates with the characterized position.

104. The positioner of

claim 98

wherein the determining means also determines an expected pressure corresponding to the characterized position and compares a pressure feedback to the expected pressure;

105. A method for detecting seat leakage in an electronically positionable valve comprising:

setting a minimum controllable valve lift point;

determining if the valve is within the minimum controllable valve lift point;

recording a time that the valve is within the minimum controllable valve lift point;

comparing the recorded time to a predetermined limit; and

performing a maintenance action in response to the recorded time exceeding the predetermined limit.

106. The method of

claim 105

wherein the maintenance action includes closing the valve.

107. The method of

claim 105

wherein the maintenance action includes signaling a user.

108. The method of

claim 105

wherein the maintenance action includes updating a maintenance record.

109. A method for detecting seat leakage in an electronically positionable valve comprising:

determining an exact valve position when the valve is closed;

closing the valve;

receiving a position feedback indicating a position of the valve;

comparing the position of the valve with the exact valve position; and

performing a maintenance action in response to the position of the valve exceeding the exact valve position.

110. The method of

claim 109

wherein the maintenance action includes signaling a user.

111. The method of

claim 109

wherein the maintenance action includes updating a maintenance record.

112. A system for detecting seat leakage in an electronically positionable valve comprising:

means for setting a minimum controllable valve lift point;

means for determining if the valve is within the minimum controllable valve lift point;

means for recording a time that the valve is within the minimum controllable valve lift point;

means for comparing the recorded time to a predetermined limit; and

means for performing a maintenance action in response to the recorded time exceeding the predetermined limit.

113. The system of

claim 112

wherein the maintenance action includes closing the valve.

114. The system of

claim 112

wherein the maintenance action includes signaling a user.

115. The system of

claim 112

wherein the maintenance action includes updating a maintenance record.

116. A positioner capable of detecting seat leakage in an electronically positionable rotary valve comprising:

means for determining an exact valve position when the valve is closed;

means for closing the valve;

a position feedback indicating a position of the valve;

means for comparing the position of the valve with the exact valve position; and

means for performing a maintenance action in response to the position of the valve exceeding the exact valve position.

117. The positioner of

claim 116

wherein the determining means uses the position feedback.

118. The positioner of

claim 116

wherein the maintenance action includes signaling a user.

119. The positioner of

claim 116

wherein the maintenance action includes updating a maintenance record.

120. A method for providing custom characterization of a valve while imposing constraints to prevent a detrimental valve characteristic, comprising:

providing a graph including a plurality of points relating flow capacity to valve position, the points illustrating the valve characteristic;

receiving a position change request of one of the points from a user;

determining if there is a slope reversal of the valve characteristic responsive to the requested position change; and

if there is a slope reversal, prompting a user for another position change.

121. The method of

claim 120

further comprising:

determining if there is an undesirable change in slope of the valve characteristic; and

if there is an undesirable change in the valve characteristic, prompting the user for another position change.

122. The method of

claim 121

further comprising:

suggesting an acceptable value for the position change.

123. The method of

claim 121

wherein the position change request is received through a graphical user interface.

125. The system of

claim 123

further comprising:

means for determining if there is a slope reversal of the valve characteristic in the valve responsive to the requested position change; and

means for prompting the user for another position change if there is a slope reversal.

124. A system for imposing constraints on a valve to prevent detrimental characterization comprising:

a graph including a plurality of points relating flow capacity to valve position, the points illustrating the valve characteristic;

means for receiving a position change request from a user;

means for determining if there is an undesirable change in slope of the valve characteristic; and

means for prompting a user for another position change if there is an undesirable change in the valve characteristic.

126. The system of

claim 124

wherein the prompting means is able to suggest an acceptable value for the position change.