Patent Application
20120167996
A valve controller is used to convert a control signal into a specific valve position. The valve controller may determine the value of the control signal within the range of possible values and use an algorithm to set the valve accordingly. The algorithm may be a straight proportion or may have a non-linear characteristic based on the particular valve controller and programming. The valve controller may set the valve anywhere between fully open and fully closed.
During installation and at other times in the life of the valve and valve controller, the valve controller may be calibrated with respect to the travel of the valve itself. Calibration of the valve controller requires use of either a built-in user interface or a calibration tool. However, a built-in user interface adds cost to the valve controller for an infrequently-used process. In some installations, connection of the calibration tool to the valve controller may be physically difficult, or in other cases a technician may want to calibrate the valve controller and discover the calibration tool is not at hand.
A valve controller may test one or more signal contacts for an indication that an automatic self-calibration routine should be initiated. In one embodiment, auxiliary terminals, for example, terminals alternately used for event inputs, may be used to activate the self-calibration routine. The valve controller may then calibrate itself using internal routines and the valve and/or actuator stops as the 0% and 100% calibration points. Self calibration may also include pressure ranging and travel performance tuning.
The valve controller may have a processor or other controller that can store a setting related to the use of the auxiliary terminals using a register or non-volatile memory. The setting may be checked when the valve controller is activated, or may be polled during operation to see if a change to the setting has been made. When programmed for event inputs, a signal or impedance change applied to the terminals may trigger an interrupt or set a flag, that when polled, causes the processor to send an alert to an external process manager or similar device.
When programmed for self-calibration a signal or impedance change applied to the terminals may cause the processor to enter the self-calibration routine. The setting for mode may be verified or changed locally using a field programming tool or may be verified or set via a remote device such as the external process manager through a network connection, for example, a HART, Profibus or other protocol network.
The valve controller may use a timer to determine a time range for activating the self-calibration mode. For example, when a short circuit is applied to the terminals, the valve controller may take steps to ensure that the short circuit is not accidental, such as might occur when installing or removing a cover. The short circuit, or other signal, may cause a timer to start. The short circuit must be removed within a predetermined time period in order to meet the criteria for entering the self-calibration mode. For example, only a short circuit applied for a period of 3-5 seconds may cause activation of the self-test mode. Obviously, other time periods may be programmed.
Instead of a short circuit, a signal may be applied to cause the self-calibration mode. The signal may be a tone of a given frequency, a predetermined voltage, etc.
The predetermined time period for which the short circuit or other signal must be applied may also be programmable. In some cases, the predetermined time period may be reduced when, for example, frequent calibration may be anticipated. In other cases, the predetermined time period may be lengthened, for example, if some likelihood for intermittent shorting of the auxiliary terminals may be present.
No separate user interface on the valve controller is required, nor is connection of an external field calibration tool. Self calibration can be canceled by a second indication, such as a brief shorting of the electrical contacts.
Although the following text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of the description is defined by the words of the claims set forth at the end of this disclosure. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims.
It should also be understood that, unless a term is expressly defined in this patent using the sentence “As used herein, the term ‘______’ is hereby defined to mean . . . ” or a similar sentence, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to in this patent in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term by limited, by implication or otherwise, to that single meaning. Finally, unless a claim element is defined by reciting the word “means” and a function without the recital of any structure, it is not intended that the scope of any claim element be interpreted based on the application of 35 U.S.C. §112, sixth paragraph.
Much of the inventive functionality and many of the inventive principles are best implemented with or in software programs or instructions and integrated circuits (ICs) such as application specific ICs. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts in accordance to the present invention, further discussion of such software and ICs, if any, will be limited to the essentials with respect to the principles and concepts of the preferred embodiments.
Valve controllers are often integrally constructed with the valves they control and may arrive at a field installation already calibrated for analog input current, pressure sensors, and travel calibration. However, in the course of setup or operation, one or more areas may require re-calibration.
Recalibration may require use of portable test equipment. In one embodiment, the test equipment may be a 475 Field Communicator, available from Emerson Process Management. However, the use of such portable test equipment may not always be convenient.
Many valve controllers provide auxiliary terminals that may be coupled to an external sensor. The valve controller may post an alert when the external sensor is activated. A valve controller below may allow the auxiliary terminals to be selectively programmed so that providing a signal to the auxiliary terminals, such as a short circuit between two terminals of the auxiliary input for a specified period, will cause the valve controller to begin a self-calibration routine.
The valve controller 100 may also include a control input 106 with control input lines 108 and 110, for example. A variety of control input signals may be supported, once such exemplary signaling scheme is a 4-20 mA current loop (4-20 mA) control signal, well known in the industry. The valve controller 100 may use the 4-20 mA control signal to proportionally control the actual valve setting. In addition to the 4-20 mA control signal, a Highway Addressable Remote Transducer (HART™) protocol signal may be superimposed on the control input signals to allow it diagnostic, maintenance, and additional process data to be communicated to the valve controller 100 via a HART signaling interface 112.
The signal input circuit 114 may include signal input terminals 116 and 118. In some embodiments, the signal input terminals 116 and 118 may be directly coupled to the processor 102, but in other cases the signal input circuit 114 may provide biasing, input transient protection, or both.
A pneumatic control 128 be used to regulate the flow of pressurized fluid, such as a gas, from a pneumatic input 122 to a pneumatic output 124. Some embodiments may use a second pneumatic output 126 depending on the type of valve being controlled. For example, some valves use a single pressure input to move a valve actuator that has a spring or other return mechanism. Other valves may use two pressure inputs to move the valve actuator in opposite directions.
A sensor input 128 may be coupled to one or more sensor inputs 130 and 132. The sensor input 128 may provide feedback to the processor as to the actual position of an actuator or the valve itself.
Also illustrated in
In operation, a 4-20 mA control signal may be received on control input lines 108 and 110. The control signal may be interpreted at the control input 106 and reported to the processor 102. Responsive to the control signal, the processor 102 may cause the pneumatic control 122 to move the actuator 136 by changing the pressure at output 124, until the actuator 136 or valve mechanism reaches a desired position as reported by the sensor input 128.
The auxiliary input 114 be a designated input programmable to different functions. When programmed in a first mode as an alert input or alarm input, placing a signal or causing an impedance change across input terminals 116 and 118 may cause the signal input circuit 114 to notify the processor 102 that an event has occurred or some external condition exists. The processor 102 may then respond according to its programming to respond to the event, for example, by sending a notification to a process controller via the HART signaling interface 112.
When programmed in a second mode as a self-calibration input, placing a signal or causing an impedance change across input terminals 116 and 118 may cause the signal input circuit to notify the processor 102 that a signal is present. The processor 102 may then respond to initiate a self-calibration routine for valve travel calibration by moving the actuator 136 to a first calibration point, that is, a first limit of valve travel, at one end of the available actuator travel and then a second calibration point, that is, a second limit of valve travel, at the other end of the available actuator travel so that the full travel of the actuator 136 or corresponding valve mechanism may be determined. When the limits of travel have been completed, a first control signal limit value may be resolved and set for the first calibration point and a second control signal limit value may be resolved and set for the second calibration point.
Preliminarily in some embodiments, the signal or auxiliary input terminals 204 and 206 may be programmed by the valve controller 100 to a mode to receive a signal for activating the self calibration routine. This programming may occur at the time of manufacture, at installation, during a field maintenance session, or remotely via a HART, Profibus, or other protocol instruction received from a remote controller. In other embodiments, the auxiliary input terminals may only be used for initiating the self calibration routine.
At block 302, the auxiliary terminals 116, 118 may be checked to determine if a short or other signal is present for a predetermined interval, for example, 3-10 seconds. Determining if a short exists may involve checking the auxiliary terminals every 30-100 milliseconds (ms) to see if the short exists. When the short or other signal is detected, a timer may be started and used to determine if the short is removed within the predetermined time range. The processor 102 may continue to check for the short every 30-100 ms. If the short is removed during the predetermined interval, operation may continue at block 304.
At block 304, the processor may determine if conditions are appropriate for running a self-calibration routine. For example, a setting may be in place that blocks self-calibration. If a condition exists indicating that a self-calibration should not be executed, the ‘no’ branch is taken to block 302. If nothing is preventing self-calibration, the ‘yes’ branch from block 304 may be taken to block 306.
At block 306, the current operating mode settings and system variables may be saved. These values may be used to restore the current state if any part of the self calibration fails or is manually aborted. Operation may continue at block 308 and the routines for calibration may be loaded and executed.
At block 310, the valve may be bumped, that is briefly moved back and forth, as an indication that the self-calibration routine has begun.
At block 312, the relay type may be determined and the self-calibration for valve/actuator travel may be performed. The relay type has to do with whether the valve controller actively drives the actuator in both directions, if the actuator is driven in one direction or the other with a spring return, etc. Various relay types are known in the industry. Travel calibration may involve driving the actuator 136 until either the actuator or the valve 134 reaches the limit of its travel. The fully opened and closed positions may be noted and saved.
At block 314, if the travel calibration completes successfully, the ‘yes’ branch from block 314 may be taken to block 316.
At block 316, an additional calibration may optionally be performed. Pressure ranging calibration involves positioning the valve at 1% and 99% of its travel and noting the pressure those travel positions. The high and low points of output pressure may be saved and used when the valve is operated in a pressure control mode.
If the ranging completes successfully, the ‘yes’ branch from block 318 may be taken to block 320.
At block 320, an automatic performance tuner may be executed. Performance tuning may be used in digital valve controller tuning. The tuning process involves moving the valve slightly and an monitoring the effects of small tuning changes to develop an optimum control response. Tuning may involve settings related to gain and feedback for valve responsiveness.
If the tuning completes successfully, the ‘yes’ branch from block 322 may be taken to block 324. At block 324 a flag or bit may be set indicating the successful conclusion of each of phase. A single success bit may be set or, in other embodiments, a success bit for each phase may be set.
In some embodiments, only one of two of the calibration phases may be performed, for example, when some phases are not appropriate for a certain operating mode or when explicitly programmed.
Returning to block 302, if the auxiliary terminals are shorted for greater than the predetermined interval, for example, greater than 10 seconds, operation may continue at block 326. If a calibration routine is already in progress, the ‘yes’ branch from block 326 may be taken and operation may continue at block 328 where the calibration routine may be aborted and an abort bit set for later polling. At block 330, the system variables and operating mode settings may be restored and operation continued at block 302.
If, at block 326, the calibration routine is not running, the ‘no’ branch from block 326 may be taken and operation may continue at block 302.
The embodiment illustrated in
Other variations of the embodiment shown in
The ability to both start and stop self-calibration routine in a valve controller without the use of an external tool or remote programming provides an additional tool for use by a technician in the field. By avoiding an extensive built-in user-interface, the valve assembly including the valve controller could be provided at a lower cost and with fewer active components that may themselves require maintenance.
Although the foregoing text sets forth a detailed description of numerous different embodiments of the invention, it should be understood that the scope of the invention is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possibly embodiment of the invention because describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the invention.
Thus, many modifications and variations may be made in the techniques and structures described and illustrated herein without departing from the spirit and scope of the present invention. Accordingly, it should be understood that the methods and apparatus described herein are illustrative only and are not limiting upon the scope of the invention.
