Abstract:
An emergency shut down valve is operated using a pressurized fluid. A pressure transmitter is operably coupleable to the source of pressurized fluid and is configured to receive an indication relative to emergency shut down valve diagnostics. The pressure transmitter responsively captures pressure readings relative to the source of pressurized fluid for a selected duration. In some embodiments, the pressure transmitter may perform diagnostics upon the captured data. In other embodiments, the captured data is provided to an external device for analysis.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 60/541,987, filed Feb. 5, 2004, the content of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to diagnostics of emergency shutdown valves.  
         [0003]     Emergency shutdown valves are designed to take a process, such as an industrial process like oil refining, to a safe state if certain pre-specified operating limits are exceeded. Emergency shutdown valves may take any of a variety of forms, for example, gate valves, butterfly valves, rotary or ball valves. An emergency valve is generally operated using a source of pressurized fluid. One method of operation involves an actuator using hydraulic or gas pressure to retain the valve in its normal, for example, open, position. When the emergency valve is to be shut, the hydraulic or gas pressure is released and a metal spring or other mechanism closes the valve. In the case of a double acting actuator, the medium controlling the actuator is redirected to close the valve. The application of the hydraulic or gas pressure is normally controlled by one or more electrically controlled solenoid valves. An electrical signal is provided to the solenoid valve(s) by an electrical control line. Any interruption of the electrical signal will operate the solenoid valves to release or divert the hydraulic or gas pressure and hence closes the valve.  
         [0004]     One of the difficulties with maintaining such emergency valves is due to the nature of the process itself. For example, a process such as oil refining is generally in continuous operation and the cost of shutting any particular line down to perform maintenance work can be very high. As a consequence emergency valves are generally not moved or otherwise operated between maintenance intervals, which may sometimes be several years. Over that time, dirt or other material may become deposited in the valve, which may become stuck and potentially inoperable in the event of an emergency.  
         [0005]     Accordingly, it is highly desirable, and in some cases required, to test emergency shutdown (ESD) valves at relatively frequent intervals to ensure that they are operable. This helps ensure the overall reliability and safety of an industrial process. When such diagnostics are performed, the system may be shut down completely, and a full-stroke test or diagnostics performed. Recent developments have allowed for diagnostics of such emergency shutdown valves to be performed without shutting down the entire process to which they are connected. These diagnostics are typically performed by partially stroking the emergency shutdown valve, and accordingly not shutting down the process.  
         [0006]     Regardless of whether the diagnostics partially stroke the ESD valve, or fully stroke it, fluid pressure provided to the emergency shutdown valve is monitored over time. A number of data points are obtained relative to the fluid pressure in the seconds following actuator or solenoid energization. The shape of the plot of pressure versus time, also referred to herein as a pressure signature, for this set of data is known to reveal a number of diagnostic conditions relative to emergency shutdown valves. Examples of ESD valve system diagnostics that can be computed, or otherwise derived, from pressure signatures include: stem shear; solenoid failure, a sticking solenoid, a restricted exhaust port, and the valve or actuator being stuck. In fact, it has been suggested that a surprising amount of ESD valve diagnostic information can be obtained merely by adding a pressure transmitter in the exhaust line of the actuator and capturing the signal profile or signature of the valve during closure with a microcomputer.  
         [0007]     One drawback of current diagnostic systems that employ a pressure transmitter providing pressure readings over time to a microcomputer is that the data obtained and stored at the microcomputer has relatively poor temporal resolution relative to the event (typically occurring in a few seconds). Thus, it would significantly improve the process of diagnosing or otherwise maintaining emergency shutdown valves if the temporal resolution could be significantly increased without unduly impacting costs, or requiring significant technician time.  
       SUMMARY OF THE INVENTION  
       [0008]     An emergency shut down valve is operated using a pressurized fluid. A pressure transmitter is operably coupleable to the source of pressurized fluid and is configured to receive an indication relative to emergency shut down valve diagnostics. The pressure transmitter responsively captures pressure readings relative to the source of pressurized fluid for a selected duration. In some embodiments, the pressure transmitter may perform diagnostics upon the captured data. In other embodiments, the captured data is provided to an external device for analysis. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a diagrammatic view of a pressure transmitter coupled to an emergency shutdown valve.  
         [0010]      FIG. 2  is a diagrammatic view of a pressure transmitter providing ESD diagnostics in accordance with an embodiment of the present invention.  
         [0011]      FIG. 3  is a flow diagram of a method of capturing ESD valve diagnostic data using a pressure transmitter in accordance with an embodiment of the present invention.  
         [0012]      FIG. 4  is a diagrammatic view of a three-dimensional chart illustrating wavelet analysis in accordance with an embodiment of the present invention.  
         [0013]      FIG. 5  shows a pressure signature contrasted of an ESD valve system having a stem shear problem contrasted with a known “good” signature. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]      FIG. 1  is a diagrammatic view of a pressure transmitter coupled to an emergency shutdown valve. Pressure transmitter  100  is fluidically coupled to pressurized gas within line  102 , which pressurized gas controls the operation of emergency shutdown valve  104 . The pressurized gas is provided by source  106 . Solenoid valve  108  is illustrated as being interposed between emergency shutdown valve  104  and source  106 . Solenoid valve  108  is energized by control line  110  when actuation of valve  104  is desired. In order to reduce the reaction time of valve  104 , one or more quick exhaust valves  112  may be provided as is known in the art.  
         [0015]     In the past, pressure readings from transmitter  100  were conveyed to a microcomputer (not shown), which stored a number of such readings over time. Then, the microcomputer could construct a chart plotting pressure measured by transmitter  100  over time. As mentioned briefly above, this approach suffers from a significant drawback. Specifically, the resolution available to the microcomputer is limited by the rate at which the pressure transmitter can obtain pressure measurements and/or communicate them to the microcomputer. While current industry standard communication protocols and process instruments may support updating many times per second, this rate may not be sufficient to capture, or otherwise convey, extremely fleeting aspects of the pressure/time diagnostics of the emergency shutdown (ESD) valve. In accordance with one embodiment of the present invention, digital data corresponding to pressure measurements is obtained at a rate faster than can be communicated by the pressure transmitter. Essentially, when so instructed, the pressure transmitter itself becomes a capture device. This allows the pressure transmitter to focus solely upon obtaining and storing as many digital representations of the pressure as possible and potentially freeing the controller of the transmitter from other tasks, such as communications.  
         [0016]      FIG. 2  is diagrammatic view of pressure transmitter  200  coupled to and providing diagnostics relative to ESD valve  104 . As illustrated at line  202 , pressure sensor  204  of pressure transmitter  200  is fluidically coupled, in any suitable manner, to emergency shutdown valve  104 . This may be accomplished merely by tapping into the pressure line feeding ESD valve  104 . Alternatively, pressure transmitter  200  may simply be disposed in the exhaust line of the actuator. Pressure sensor  204  can be any suitable structure that has an electrical characteristic that varies with an applied pressure. For example, pressure sensor  204  can be a known capacitance-type diaphragm pressure sensor. Preferably, however, sensor  204  is a semiconductor-based pressure sensor. These types of pressure sensors are taught in U.S. Pat. No. 5,637,802, assigned to the Assignee of the present invention. Such semiconductor-based pressure sensors generally provide a capacitance that varies with deflection of a portion of the semiconductor sensor. The deflection is in response to an applied pressure.  
         [0017]     The use of semiconductors, and in particular, sapphire provides a number of advantages. Sapphire is an example of a single-crystal material that when properly fusion-bonded has no material interface between the two bonded portions. Thus, the resulting structure is exceptionally robust. Additionally, semiconductor-based sensors have extremely beneficial hysteresis characteristics as well as an extremely high frequency response. Additional information related to semiconductor-based pressure sensors can be found in U.S. Pat. Nos. 6,079,276; 6,082,199; 6,089,907; 6,484,585; and 6,520,020, all of which are assigned to the Assignee of the present invention. Accordingly, even extremely fleeting pressure events occurring during the ESD diagnostics will be electrically measurable using such a pressure sensor.  
         [0018]     Analog-to-digital converter  206  is coupled to pressure sensor  204  and provides a digital indication to controller  208  based upon the electrical characteristic of pressure sensor  204 . In one embodiment, analog-to-digital converter  206  can be based on sigma-delta converter technology. Each converted digital representation of the pressure is provided to controller  208 . Sigma-delta converters are often used in the process measurement and control industry due to their fast conversion times and high accuracy. Sigma-delta converters generally employ an internal capacitor charge pumping scheme that generates a digital bitstream that is analyzed, generally by counting positive 1&#39;s over a set interval. The digital values converted by converter  206  are preferably provided to controller  208  along line  210 .  
         [0019]     In accordance with another embodiment of the present invention, converter  206  can provide the raw digital bitstream to controller  208  along line  212  (illustrated in phantom). This bitstream usually has a frequency that is many orders of magnitude higher than the conversion frequency of converter  206 . For example, a sigma-delta converter may provide a digital bitstream that has a frequency of approximately 57 kHz. Accordingly, when transmitter  200  needs to perform a high-speed capture, it can do so in one of two ways. First, it may simply use controller  208  to store digital values provided on line  210  at the conversion rate of converter  206 , which values are then stored in memory  214  for later analysis. Accordingly, the rate at which these values are acquired and stored is dictated solely by the conversion rate of converter  206 . In distinct contrast, in the past, a microcomputer communicating with a pressure transmitter would be limited by the rate at which the two devices could communicate as well as the conversion rate of an analog-to-digital converter in the pressure transmitter.  
         [0020]     For maximum resolution, pressure transmitter  200  can employ converter  206  to store the raw bitstream from line  212  directly into memory  214 . Thus, a sigma-delta converter providing a digital bitstream having a frequency of approximately 57 kHz will provide 57,000 bits to be stored in memory  214  for each second that the capture occurs. In many ESD diagnostics, such as those listed above, the tests can be completed in approximately 8 seconds or less. Thus, it is preferred that memory  214  have at least 64 kilobytes of capacity available for capture data. However, in embodiments where the pressure transmitter will store one or more pressure-time valve profiles, such as a profile of a known “good” valve, additional capacity would be required.  
         [0021]     Controller  208  is preferably a microprocessor that is adapted to operate on relatively low power levels, such as those commonly present in field devices such as pressure transmitters. Controller  208  is coupled to communication module  220 , which is operably coupled to loop terminals  222 . Communication module  200  allows transmitter  200  to communicate upon a process communication loop in accordance with a process industry standard protocol such as, but not limited to, FOUNDATION™ Fieldbus, HART®, Profibus-PA, Modbus, Controller Area Network (CAN), or others. Power module  224  is also preferably coupled to loop terminals  222  and is adapted to provide operating power to other elements within pressure transmitter  200  from electrical energy received through terminals  222 . For example, some industry standard communication protocols such as HART® and FOUNDATION™ Fieldbus are able to provide operating power over the same wires through which communication is effected.  
         [0022]     While transmitter  200  is described with respect to a power module  224  and communication module  220  coupled to a process communication loop through terminals  222 , embodiments of the present invention may also be practiced with a pressure transmitter that is not coupled to any other devices through wires. For example, power module  224  could, instead, be an internal power source such as a storage cell or it could be an energy converter such as a solar cell, or any combination thereof. Additionally, communication module  220  could be a wireless communication module employing wireless communication, such as radio frequency or infrared communication techniques.  
         [0023]      FIG. 3  is a flow diagram of a method of capturing ESD valve diagnostic data using a pressure transmitter in accordance with an embodiment of the present invention. Method  300  begins when a pressure transmitter, such as transmitter  200 , receives a notification that capture is to begin, as illustrated at block  302 . The notification can be transmitted to the pressure transmitter over a process industry communication loop, or provided to the pressure transmitter locally by a technician. Once the transmitter receives the notification that capture is to begin, block  304 , illustrated in phantom, is optionally performed. Block  304  is used to shut down any pre-selected processes or activities within the pressure transmitter that are not directly related to or necessary for data capture. Thus, if controller  208  typically devotes a percentage of its processing time to listening to communications on the process communication loop, that activity can be ceased, and the availability of controller  208  to facilitate high speed data capture can be increased. Once optional block  304  has been completed, controller  208  will reset or otherwise initialize a timer or counter that will be used to measure the duration of the capture event. For example, as described above, many ESD diagnostics can be completed by obtaining approximately 8 seconds of captured data. In such cases, the timer within controller  208  will be set to 0 seconds at the beginning of capture and ultimately, after 8 seconds have elapsed, the capture event will cease.  
         [0024]     Once the timer or counter is initialized, control passes to block  308  where controller  208  obtains a digital value from analog-to-digital converter  206 . The digital value can be a finished analog-to-digital conversion or a single bit in the bitstream. At block  310 , the digital value obtained by controller  208  from analog-to-digital converter  206  is stored, preferably in memory  214 . Once the value is stored, control passes to block  312  where the timer or counter initialized in block  306  is evaluated to determine if the capture duration has elapsed. If not, control returns to block  308  along line  314  and the process of obtaining and storing digital values repeats. However, if the capture is complete, control passes to block  316  along line  318 . At block  316 , an analysis of the pressure data captured over time is accomplished. This analysis can be done by either the pressure transmitter itself or by an external device. If the analysis is to be performed by an external device, the captured block of data is preferably communicated to the external device using communications module  220 .  
         [0025]     One important tool that is useful in the analysis of the captured data is a technique known as wavelet analysis. Wavelet analysis is used for transforming a time-domain signal into the frequency domain, which, like a Fourier transformation, allows the frequency components to be identified. However, unlike a Fourier transformation, in a wavelet transformation the output includes information related to time. This may be expressed in the form of a three-dimensional graph ( 400  in  FIG. 4 ) with time shown on one axis, frequency on a second axis and signal amplitude on a third axis. A discussion of wavelet analysis is given in  On - Line Tool Condition Monitoring System With Wavelet Fuzzy Neural Network , by L. Xiaoli et al., Eight JOURNAL OF INTELLIGENT MANUFACTURING, pgs. 271-276 (1997). In performing a continuous wavelet transformation, a portion of the sensor signal is windowed and convolved with a wavelet function. This convolution is performed by superimposing the wavelet function at the beginning of a sample, multiplying the wavelet function with the signal and then integrating the results over the sample period. The result of the integration is scaled and provides the first value for continuous wavelet transform at time=0. This point may then be mapped onto a three-dimensional plane. The wavelet function is then shifted right (forward in time) and the multiplication and integration steps are repeated to obtain another set of data points, which are mapped onto the three-dimensional space. This process is repeated and the wavelet is moved (convolved) through the entire signal. The wavelet function is then scaled, which changes the frequency resolution of the transformation, and the above steps are repeated.  
         [0026]     Other types of signal analysis tools can also be used in accordance with embodiments of the present invention. Such techniques include, but are not limited to, learning techniques, neural networks, and fuzzy logic. Additionally the signal analysis techniques taught in U.S. Pat. No. 6,397,114 may also be used to provide ESD valve system diagnostics in accordance with embodiments of the present invention. Further, any analysis that allows one signal to be effectively contrasted to another signal can be employed. Thus, embodiments of the present invention even include providing the captured signature to a human operator for review.  
         [0027]     Once the ESD pressure signature is captured by the pressure transmitter, it is preferably analyzed by comparing the signature to known pressure signature profiles of specific ESD valve system problems. Examples of such problems/signatures include stem shear, solenoid failure, a sticking solenoid, a restricted exhaust port, as well as a valve or actuator sticking. These comparative diagnostics can be performed by either the pressure transmitter or an external device.  
         [0028]     In embodiments where the comparison is performed by the pressure transmitter, any of analytical techniques listed above can be used.  FIG. 5  shows a pair of pressure signatures. The solid line  500  is a signature indicative of known “good” ESD valve system operation. The known “good” signature can be obtained by the transmitter itself by providing it with an indication that it is coupled to a fully operation system, and allowing it to capture a signature. Alternatively, the “good” signature could be sent to the transmitter via the communications module. Dashed line  502  is follows a path that is identical to line  500  except for regions  504  and  506 . In these regions the ESD system under test drops to a slightly lower pressure than the known “good” signature. This particular behavior is indicative of valve shear in the ESD valve system. Any number of techniques could be used to identify this pattern. However, simple recording the magnitude of local minima of a ESD valve system and comparing those values with local minima for a known “good” system would indicate the valve shear problem. Regardless of the techniques used, it is preferred that the results of the comparison be communicated by the pressure transmitter. Thus, if the pressure transmitter determines that the signature obtained during the capture resembles a known failure signature (either stored within the transmitter or sent to it), within a selected or arbitrary window, an indication of that error is provided by the pressure transmitter.  
         [0029]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.