Patent Publication Number: US-9428994-B2

Title: Blowout preventer monitor with trigger sensor and method of using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to U.S. Provisional Application No. 61/842,232 filed on Jul. 2, 2013, the entire contents of which are hereby incorporated by reference herein. This patent application is also a continuation-in-part of U.S. Non-Provisional application Ser. No. 13/168,594 filed on Jun. 24, 2011, which claims priority to U.S. Provisional Application No. 61/360,783 on Jul. 1, 2010, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to techniques for performing wellsite operations. More specifically, the present disclosure relates to techniques, such as blowout preventers (BOPs), packers, and/or ram blocks, for sealing wellbores. 
     Oilfield operations may be performed to locate and gather valuable downhole fluids. Oil rigs are positioned at wellsites and downhole tools, such as drilling tools, are deployed into the ground to reach subsurface reservoirs. Once the downhole tools form a wellbore to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of fluids from the reservoir. Tubing or pipes may be positioned in the wellbore to enable the passage of subsurface fluids to the surface. 
     Leakage of subsurface fluids may pose a significant environmental threat if released from the wellbore. Equipment, such as blow out preventers (BOPs), may be positioned about the wellbore to form a seal about pipes therein to prevent leakage of fluid as it is brought to the surface. In some cases, the BOPs employ rams and/or ram blocks that seal the wellbore. Some examples of BOPs and/or ram blocks are provided in U.S. Pat. Nos. 4,647,002, 6,173,770, 5,025,708, 7,051,989, 5,575,452, 6,374,925, 2008/0265188, 5,735,502, 5,897,094, 7,234,530, 8,544,538, 8,136,247, 2010/0243926, and 2012/0012340. The location of the ram and/or ram block of a BOP may be measured by visually looking at a tail shaft of the ram blocks. Ram position sensors may be provided as described, for example, in US Patent/Application No. 2008/0197306, U.S. Pat. Nos. 4,922,423, 5,320,325, 5,407,172, and 7,274,989. 
     SUMMARY 
     In at least one aspect, the disclosure relates to a monitor for a blowout preventer of a wellbore. The blowout preventer includes a housing, at least one ram slidably positionable in the housing to form a seal about the wellbore, and an actuator. The actuator comprises a cylinder with a piston slidably movable therein. The piston is operatively connectable with the ram and movable therewith. The monitor includes a monitor base operatively connectable to the cylinder (the monitor base having an interior side inside the cylinder and an exterior side outside the cylinder), an interior plate positionable inside the cylinder about the interior side of the base (the interior plate operatively connectable to the piston and movable therewith), an exterior plate positionable outside the cylinder about the exterior surface of the monitor base (the exterior plate coupled by magnets to the interior plate and rotatable therewith), and a trigger sensor operatively connectable about the monitor base and the exterior plate to detect rotation thereof whereby a position of the ram may be determined. 
     The monitor may also include a cable operatively connecting the interior plate to the piston. The interior plate may include a pulley wheel, with the cable disposable about the pulley wheel. The interior plate may include a cover with a hole to pass the cable therethrough, and/or a rotary spring. The monitor base may have an interior pocket to receive the interior plate, and may have a shaft operatively connectable to the interior plate. The trigger sensor may include a sensor base and a trigger, the sensor base may be operatively connectable to the monitor base and have a rod extending into the exterior plate, and the trigger may be positionable about the exterior plate to deflect the rod to an offset position detectable by the sensor base as the exterior plate rotates whereby a position of the ram may be determined. 
     The exterior plate may have a trigger pocket therein to receive the trigger, the trigger may include a spring and a plunger, with the plunger urged by the spring against the rod, the trigger sensor may include a bearing positionable in the exterior plate and having a hole therethrough to receive the rod, with the trigger engagable with the bearing to deflect the rod, and/or the sensor base may be fixedly positioned in a sensor receptacle of the monitor base with the rod deflectingly extending from the sensor base. The rod tip of the rod may extend from the sensor base into the trigger pocket, and the rod tip may be movable in the trigger pocket as the interior plate rotates. 
     The trigger sensor may include a sensor base operatively connectable to the monitor base and having a rod extending to the exterior plate to detect keys along a periphery thereof. The keys may include teeth, and/or black and white portions. The exterior plate may include base plate and the ring, and a dial operatively connectable to the base plate and movable therewith. The exterior plate may be rotatable via the magnets with the interior plate, and the exterior plate may have a dial thereon rotatable with the interior plate. The trigger sensor may include a strain gauge. The magnets may include interior magnets operatively connectable between the interior plate and the monitor base. The magnets may include exterior magnets operatively connectable between the exterior plate and the monitor base. The monitor base may include an end cap of the cylinder. The monitor may also include at least one seal, and/or an accelerometer. 
     In yet another aspect, the disclosure relates to a monitoring system for a wellbore penetrating a subterranean formation. The system includes a blowout preventer positionable about the wellbore and a monitor operatively connectable with the blowout preventer. The blowout preventer includes a housing, at least one ram slidably positionable in the housing to form a seal about the wellbore, and an actuator comprising cylinders with pistons slidably movable therein. The piston is operatively connectable with the at least one ram and movable therewith. The monitor includes a monitor base, an interior plate, an exterior plate, and a trigger sensor. The monitor base is operatively connectable to the cylinder and has an interior side inside the cylinder and an exterior side outside the cylinder. The interior plate is positioned inside the cylinder about the interior side of the base, and is operatively connectable to the piston and movable therewith. The exterior plate is positioned outside the cylinder about the exterior surface of the monitor base, and is coupled by magnets to the interior plate and is movable therewith. The trigger sensor is operatively connectable to the monitor base, and has a rod positionable about the exterior plate to detect rotation thereof whereby a position of the ram may be determined. The system may include an inspector and/or a controller operatively connectable to the trigger sensor. The inspector may be a remote operated vehicle and/or an operator. 
     In yet another aspect, the disclosure relates to a method of monitoring a blowout preventer of a wellbore penetrating a subterranean formation. The blowout preventer includes a housing, at least one ram slidably positionable in the housing to form a seal about the wellbore, and an actuator comprising cylinders with pistons slidably movable therein. The piston is operatively connectable with the at least one ram and movable therewith. The method involves operatively connecting a monitor including a monitor base, an interior plate, an exterior plate, and a trigger sensor to the blowout preventer by operatively connecting the monitor base to the cylinder, an interior plate about an interior surface of the monitor base, and an exterior plate about an exterior surface of the monitor base. The method further involves rotating the interior plate with the rams via a cable, rotating the exterior plate with the interior plate via the magnets, and determining a position of the rams by sensing rotation of the exterior plate with the trigger sensor. 
     The method may also include collecting data from the trigger sensor, passing data from the trigger sensor to a surface unit, and/or adjusting the blowout preventer based on the determining. The trigger sensor may include a sensor base positionable in the monitor base and a rod extending from the sensor base into the exterior plate and the determining may involve detecting a position of the exterior plate by deflecting the rod and measuring a position of the rod with the sensor base during the rotating. The trigger sensor may include a sensor base positionable in the monitor base and a rod extending from the sensor base into the exterior plate, and the determining may involve detecting a position of the exterior plate by detecting keys along a periphery of the exterior plate with the trigger sensor. 
     In another aspect, the invention relates to a blowout preventer for sealing a tubular of a wellbore. The wellbore penetrates a subterranean formation. The blowout preventer has a housing having a bore therethrough for receiving the tubular, at least one ram slidably positionable in the housing (each of the rams having a ram block for sealing engagement about the tubular), an actuator for selectively driving the ram block (the actuator having a piston slidably positionable in a cylinder), and a monitor for detecting the piston therein. The monitor includes a visual indicator on an exterior of the cylinder. The visual indicator is operatively coupled to the piston for displaying a position of the piston as the piston travels within the cylinder whereby a position of the ram may be determined. 
     The visual indicator may have a cable operatively connected to the piston. The cable may be operatively connectable to a dial via a pulley and rotatable thereby as the piston moves within the cylinder. The visual indicator may also have at least one gear for operatively coupling the pulley to the dial. The visual indicator may have a magnetic coupler for coupling the dial to the pulley. The visual indicator may have a housing integral with the cylinder. The visual indicator may also have a plurality of flags positioned on a flag rod. The plurality of flags may be selectively raisable as the piston passes adjacent thereto. The visual indicator may have a magnet slidably positionable on a guide in response to a magnet on the piston passing adjacent thereto. The visual indicator may have a transparent case with a plurality of metal filings movably positionable therein in response to a magnet on the piston passing adjacent thereto. The visual indicator may have a transparent case with a magnetic indicator movably positionable therein in response to a magnet on the piston passing adjacent thereto. The blowout preventer may also have a visual sensor for detecting the visual indicator. 
     The blowout preventer may also have an electrical indicator for detecting a position of the piston. The electrical indicator may have a magnet slidably positionable on a guide in response to a magnet on the piston passing adjacent thereto, and at least one Hall Effect sensor for detecting a position of the magnet on the guide. The electrical indicator may be an inductive resistance sensor comprising a coil disposed about the cylinder. The electrical indicator may have a top end ultrasonic sensor at a top end of the cylinder and a bottom end ultrasonic sensor at a bottom end of the cylinder for detecting the piston when adjacent thereto. The electrical indicator may have an ultrasonic limit sensor. The electrical indicator may be a laser sensor. The electrical indicator may have a capacitive displacement sensor. The electrical indicator may be a sonar sensor for emitting sonar waves and sensing the waves rebounded by the piston. The electrical indicator may have at least one proximity sensor. The electrical indicator may have a flow sensor for detecting the flow of fluid through a chamber of the cylinder as the piston passes therein. 
     In yet another aspect, the invention relates to a system for sealing a tubular of a wellbore. The system has a blowout preventer and an inspector for inspecting visual indicator. The blowout preventer has a housing having a bore therethrough for receiving the tubular, at least one ram slidably positionable in the housing (each of the rams having a ram block for sealing engagement about the tubular), an actuator for selectively driving the ram block (the actuator having a piston slidably positionable in a cylinder), and a monitor for detecting the piston therein. The monitor includes a visual indicator on an exterior of the cylinder. The visual indicator is operatively coupled to the piston for displaying a position of the piston as the piston travels within the cylinder whereby a position of the ram may be determined. 
     The blowout preventer has a housing having a bore therethrough for receiving the tubular, at least one ram slidably positionable in the housing (each of the rams having a ram block for sealing engagement about the tubular), an actuator for selectively driving the ram block (the actuator having a piston slidably positionable in a cylinder), and a monitor for detecting the piston therein. The monitor includes a visual indicator on an exterior of the cylinder. The visual indicator is operatively coupled to the piston for displaying a position of the piston as the piston travels within the cylinder whereby a position of the ram may be determined. 
     The inspector may be a human or a remote operated vehicle (ROV). The system may also have a surface unit for receiving data from the monitor, an electrical indicator for detecting a position of the piston, a receiver for communicating signals with the electrical indicator, and/or at least one sensor for detecting wellsite parameters. 
     In yet another aspect, the invention relates to a method of monitoring a blowout preventer. The method involves positioning the blowout preventer about a tubular, activating at least one of the visual indicators of the monitor as the piston passes adjacent thereto, and inspecting the visual indicators. The blowout preventer has a housing having a bore therethrough for receiving the tubular, at least one ram slidably positionable in the housing (each of the rams having a ram block for sealing engagement about the tubular), an actuator for selectively driving the ram block (the actuator having a piston slidably positionable in a cylinder), and a monitor for detecting the piston therein. The monitor includes a visual indicator on an exterior of the cylinder. The visual indicator is operatively coupled to the piston for displaying a position of the piston as the piston travels within the cylinder whereby a position of the ram may be determined. The method may also involve sensing a position of the piston with an electrical indicator, manually viewing the visual indicators, sensing the visual indicator for activation, and/or passing data from the monitor to a surface unit. 
     Finally, in yet another aspect, the invention relates to a blowout preventer for sealing a tubular of a wellbore. The blowout preventer includes a housing having a bore therethrough for receiving the tubular, at least one ram slidably positionable in the housing (each of the at least one rams having a ram block for sealing engagement about the tubular), an actuator for selectively driving the ram block (the actuator comprising a piston slidably positionable in a cylinder), and a monitor for detecting the piston. The monitor has a housing with a cable therein. The cable is operatively connectable to the piston and movable therewith for activating a visual indicator on an exterior of the housing whereby a position of the ram may be displayed. 
     The monitor also may also have a sensor operatively connected for detecting movement of the cable and/or a communication link for passing data from the sensor to a surface unit. The visual indicator may have a dial rotationally movable by the cable. The monitor may also have a magnetic coupler inside of the housing for coupling the cable to the dial. The monitor also has at least one gear for operatively coupling the cable to the dial. The monitor may also have at least one pulley. The housing may be integral with the cylinder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate example embodiments of this disclosure and are, therefore, not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
         FIG. 1  shows a schematic view of an offshore wellsite having a blowout preventer (BOP) for sealing a tubular. 
         FIG. 2  shows a schematic perspective view of the BOP of  FIG. 1 . 
         FIG. 3  shows a schematic side view of the BOP of  FIG. 2  having one or more actuator(s) and a BOP monitoring system. 
         FIGS. 4A-4N  show schematic cross-sectional views of various versions of a portion of an actuator and a monitoring system operatively connected thereto. 
         FIGS. 5A-5D  show schematic cross-sectional views of additional versions of an actuator and a monitoring system operatively connected thereto. 
         FIG. 6  depicts a method of monitoring a BOP. 
         FIG. 7  depicts a schematic view of a BOP with actuators and a BOP monitor. 
         FIG. 8  is a schematic view of a portion of the BOP depicting a BOP monitor therein, the BOP monitor including a monitor base, interior and exterior plates, and a trigger sensor. 
         FIG. 9A  is a schematic diagram depicting the trigger sensor of the BOP monitoring system.  FIG. 9B  is a schematic diagram depicting operation of the trigger sensor at various angles. 
         FIGS. 10A and 10B  show exterior end and interior end views, respectively, of a BOP monitor.  FIG. 10C  shows a partial cross-sectional view of the BOP monitor. 
         FIGS. 11A-11C  show partial cross-sectional, exterior exploded, and interior exploded views, respectively, of a BOP monitor.  FIG. 11D  shows an exploded view of an alternate version of the BOP monitor. 
       FIGS.  12 A 1  and  12 A 2  are schematic views of a BOP monitor in an initial position. FIGS.  12 B 1  and  12 B 2  are schematic views of the BOP monitor in a rotated position. 
         FIG. 13A  is a cross-sectional view of the BOP monitor of FIG.  12 A 1  taken along line  13 A- 13 A.  FIG. 13B  is a cross-sectional view of the BOP monitor of FIG.  12 A 2  taken along line  13 B- 13 B. 
         FIG. 14  is a flow chart depicting a method of monitoring a BOP. 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows includes exemplary apparatus, methods, techniques, and/or instruction sequences that embody techniques of the present subject matter. However, it is understood that the described embodiments may be practiced without these specific details. 
     The invention is directed at techniques for providing monitoring and/or measuring of the operation of the blowout preventer (BOP). The BOP may be provided with a monitor to detect, for example, a position (or location) of a ram of the BOP. These techniques may be used to provide monitoring, such as visual or electrical monitoring, of the BOP (e.g., from the surface), such as while the BOP is in use on the seabed. Such monitoring techniques involve one or more of the following, among others: determination of BOP function, determination of ram position, determination of sealed position, constant monitoring of the ram position within the BOP, adaptability to wellsite equipment (e.g., various pipes diameters). 
     Blowout preventers (BOPS) may include a housing positioned about a wellbore to receive a tubing therethrough and to provide a seal thereabout, for example, during a blowout. The BOP also has rams movably positionable in the housing to engage the tubular and/or form a seal about the wellbore. A BOP monitor may be provided about the BOP to detect movement of the rams and determine a position thereof. The BOP monitor may include a monitor base disposable in the cylinder, an interior plate coupled by a cable to the ram, an exterior plate magnetically coupled to the interior plate, and sensors (e.g., strain gauges) to detect the rotation of the plates and, therefore, displacement and position of the rams. 
     Blowout Preventer 
       FIG. 1  depicts an offshore wellsite  100  having a seal assembly  102  configured to seal a wellbore  105  extending into in a seabed  107 . As shown, the seal assembly  102  is positioned in a blowout preventer (BOP)  108  that is part of a subsea system  106  positioned on the seabed  107 . The subsea system  106  may also comprise a pipe (or tubular)  104  extending from the wellbore  105 , a wellhead  110  about the wellbore  105 , a conduit  112  extending from the wellbore  105  and other subsea devices, such as a stripper and a conveyance delivery system (not shown). The BOP  108  may have a BOP monitoring system (or BOP monitor)  103  for monitoring the operation of the BOP  108 . While the wellsite  100  is depicted as a subsea operation, it will be appreciated that the wellsite  100  may be land or water based, and the seal assembly  102  may be used in any wellsite environment. 
     A surface system  120  may be used to facilitate operations at the offshore wellsite  100 . The surface system  120  may include a rig  122 , a platform  124  (or vessel) and a surface controller  126 . Further, there may be one or more subsea controllers  128 . While the surface controller  126  is shown as part of the surface system  120  at a surface location and the subsea controller  128  is shown as part of the subsea system  106  in a subsea location, it will be appreciated that one or more controllers may be located at various locations to control the surface and/or subsea systems. 
     To operate one or more seal assemblies  102  and monitor the BOP monitoring system  103  and/or other devices associated with the wellsite  100 , the surface controller  126  and/or the subsea controller  128  may be placed in communication therewith. The surface controller  126 , the subsea controller  128 , and/or any devices at the wellsite  100  may communicate via one or more communication links  134 . The communication links  134  may be any suitable communication means, such as hydraulic lines, pneumatic lines, wiring, fiber optics, telemetry, acoustics, wireless communication, any combination thereof, and the like. The seal assembly  102 , the BOP monitoring system  103 , the BOP  108 , and/or other devices at the wellsite  100  may be automatically, manually and/or selectively operated via the surface and subsea controllers  126  and/or  128 , respectively. 
     A remote operated vehicle (ROV)  121  may optionally be provided to travel below the surface and inspect the BOP monitoring system  103 . The ROV  121  may be provided with a camera  135  to display images of the BOP monitoring system  103  and/or electrical communicators (e.g., communication link  134 ) for coupling to the BOP monitoring system  103 . The ROV  121  may be in communication with the surface unit  126  and/or BOP  108  via a communication link  136 . In some cases, a diver or other inspector may be used to visually inspect the BOP monitoring system  103 . 
       FIG. 2  shows a schematic view of a BOP  108  that may be used as the BOP  108  of  FIG. 1 . The BOP  108  is schematically depicted as a cuboid-shaped device having a bore (or channel)  220  therethrough for receiving the pipe  104 . The BOP  108  is also provided with a channel  222  therethrough for receiving the seal assembly  102 . While the BOP  108  is depicted as having a specific configuration, it will be appreciated that the BOP  108  may have a variety of shapes, and be provided with other devices, such as sensors (not shown). An example of a BOP that may be used is described in U.S. Pat. No. 5,735,502, the entire contents of which is hereby incorporated by reference. 
     The seal assembly  102  comprises one or more rams  202  for sealing the BOP  108 . The rams  202  may be any suitable device for sealing the interior of the BOP  108  and/or severing the pipe  104 , for example rams, ram blocks, and/or shearing blades. Upon actuation of the rams  202  of the seal assembly  102 , the rams  202  may move along the channel  222  toward the pipe  104 . The seal assembly  102  may seal the pipe  104  within the BOP  108 , thereby preventing fluids, such as wellbore fluids and/or sea water, from passing through the BOP  108 . Further, the seal assembly  102  may severe the pipe  104  if the seal assembly  102  has shearing blades. 
       FIG. 3  shows a schematic side view of the BOP  108  of  FIG. 2  having an actuator  300  coupled to each of the rams  202 . The actuator  300  may be configured to move the rams  202  between an un-actuated position wherein the rams  202  are not engaged with the pipe  104  and an actuated position (as shown in  FIG. 3 ) wherein the rams  202  are engaged with the pipe  104 . In the un-actuated position, the pipe  104  may move through the BOP  108  and into and/or out of the wellbore  105  (see, e.g.,  FIG. 1 ). In the actuated position, the pipe  104  and/or the central bore  220  of the BOP  108  may be sealed about pipe  104  by the rams  202 . 
     The actuator  300  as shown, is a hydraulic actuator configured to move a piston  304  within a cylinder  306  using hydraulic fluid supplied to the actuator  300 . The cylinder  306  has a side  307 , a head  309  and a rear  311 . The piston  304  is slidably movable within the cylinder  306  by, for example, hydraulic pressure selectively applied thereto. The piston  304  may couple to a rod  308  (or ram shaft) that is configured to move the rams  202  as piston  304  moves. Although the actuator  300  is shown as a hydraulic piston and cylinder, the actuator  300  may be any suitable actuator for moving the rams  202  between the actuated and the un-actuated positions. 
     As the piston  304  moves within the cylinder  306 , the BOP monitoring system  103  may monitor the location of the piston  304 . With the location of the piston  304  determined, the location of the rams  202  within the BOP  108  may be determined. The data collected by the BOP monitoring system  103  may be sent via the communication links  134  to the surface and subsea controller(s)  126 / 128  in order to, for example, determine how the BOP  108  is operating. The BOP monitoring system  103  may be any suitable system for determining the location of the pistons  304 , the rods  308  and/or the rams  202  within the BOP  108 . The monitoring system  103  may also be capable of determining other downhole parameters of the BOP  108 , its components and/or associated downhole conditions. 
     Blowout Preventer Monitoring Systems 
       FIGS. 4A-4N  depict cross-sectional views of a portion of the actuator  300   a - m  having various versions of a monitoring system  103   a - m  usable as the actuator  300  and BOP monitoring system  103  of  FIG. 3 . As shown in each of these figures, the piston  304  is slidably movable within the cylinder  306 . The monitoring systems  103   a - m  are each positionable about the cylinder  306  and have devices for detecting a position of the piston  304  therein. Each piston  304  is operatively connectable to a ram  202  (see  FIGS. 2 and 3 ) and, therefore, a position of the rams  202  (and/or components thereof) may also be determined. A visual indicator sensor S may optionally be positioned about the monitoring systems for detecting activation, position, or other parameters of the wellsite and/or components, such as the monitoring system  103   a - m.    
       FIG. 4A  depicts an actuator  300   a  with a BOP monitoring system  103   a  as an inductive resistance sensor  400 . The inductive resistance sensor  400  may have one or more coils  402  that wrap around the outside of the side  307  of the cylinder  306 . A current may be supplied to the coils  402  and a resistance in the coils  402  may be measured during the operation of the actuator(s)  300   a.    
     The piston  304  travels within the cylinder  306  between the cylinder head  309  and the cylinder rear  311  of the BOP  108 . The resistance in the coils  402  changes as a function of the location of the piston  304 . The coils  402  may individually change as the piston  304  passes thereby, thus indicating that the piston  304  is adjacent to a certain coil  402 . The changes in resistance may be used to determine the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The inductance of the coils may be measured and received by the ROV  121  and/or the surface unit  126  ( FIG. 1 ) to provide an electrical indication of the location of the piston  304  and the ram  202 . Sensor S may be provided to pass signals from the coils  402  to a receiver positioned about the wellsite  100 . A visual indicator, such as those provided herein, may also optionally be coupled to the monitoring system  103   a  to provide a visual indication of position upon activation by the monitoring system  103   a.    
       FIG. 4B  depicts an actuator  300   b  with a BOP monitoring system  103   b  as a magnetic flag sensor  410 . The magnetic flag sensor  410  may have one or more magnetic flags  412  located on the outside of a side  307  of the cylinder  306 . Each of the magnetic flags  412  may be secured to the cylinder  306  on an axis  414  that allows the magnetic flag  412  to rotate thereabout in response to a piston magnet  416  passing thereby. Each magnetic flag  412  may be magnetic, or have a magnet thereon. Each magnetic flag  412  may be at a downward position gravitationally, and raise as the piston magnet  416  passes thereby. 
     The piston magnet  416  may be any magnet secured to, or proximate the piston  304 . As the piston  304  travels within the cylinder  306  between the cylinder rear  311  and the cylinder head  309 , the piston magnet  416  raises the magnet flags  412  proximate the piston  304 . The raised magnet flags  412  may be used to provide a visual indication of the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be indicated. The sensor S may also be operatively coupled to one or more flags to provide an electrical and/or visual indication of the activation of a given flag. The sensor S may pass the signal to various components for communicating a position of the piston  304 . 
       FIG. 4C  depicts an actuator  300   c  with a BOP monitoring system  103   c  as a sliding magnetic sensor  418 . The sliding magnetic sensor  418  may have one or more sliding magnets  420  secured to a guide rod  422  located on the outside of the side  307  of the cylinder  306 . Each of the sliding magnets  420  may be secured to the guide rod  422  in a manner that allows the sliding magnet  420  to translate along the guide rod  422  in response to the movement of the piston magnet  416 . 
     As the piston  304  travels within the cylinder  306  between the cylinder rear  311  and the cylinder head  309 , the piston  304  with a magnet  416  thereon translates the sliding magnet  420  proximate the piston  304 . The location of the sliding magnet  420  may provide a visual indicator of the piston  304 . Limit switches or other devices, such as sensor S, may also be used to detect and/or communicate the position of the sliding magnet  420  along the guide rod  422 . The sliding magnet  420  location may be used to determine the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
       FIG. 4D  depicts an actuator  300   d  and a BOP monitoring system  103   d  as an ultrasonic sensor  424 . The ultrasonic sensor  424  may have one or more ultrasonic inducers  426  located around the outside of side  307  of the cylinder  306 . Each of the ultrasonic inducers  426  produce ultrasonic waves  428  that are directed into an interior of the cylinder  306  and then detected by a receiver  429 . As shown, the receiver  429  is positioned in the BOP  108 . 
     Changes in the ultrasonic waves  428  may indicate the location of the piston  304  proximate to one or more of the ultra sonic inducers  426 . As the piston  304  travels within the cylinder  306  between the cylinder rear  311  and the cylinder head  309 , the detected changes in the ultrasonic waves  428  may be used to determine the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The ultrasonic waves detected by the receiver  429  may be passed to the ROV  121  and/or the surface unit  126  ( FIG. 1 ) to provide an indication of the location of the piston  304  and the ram  202 . The sensor S may also be operatively coupled to one or more ultrasonic inducers  426  to provide an electrical and/or visual indication of the activation of a given ultrasonic inducer. The sensor S may pass the signal to various components, such as receiver  429 , for communicating a position of the piston  304 . A visual indicator, such as those provided herein, may also optionally be coupled to the monitoring system  103   d  to provide a visual indication of position upon activation by the monitoring system  103   d.    
       FIG. 4E  depicts an actuator  300   e  and a BOP monitoring system  103   e  as an ultrasonic limit sensor  430 . The ultrasonic limit sensor  430  may have two ultra sonic inducers  426 ,  427  each located proximate a travel limit of the piston  304  within cylinder  306 . For example, one of the ultrasonic inducers  426  may be located proximate the cylinder rear  311  and the second ultrasonic inducer  427  may be located adjacent the side  307  of the cylinder  306 . The second ultrasonic inducer  427  on the side  307  may be located proximate the travel limit adjacent cylinder head  309  of the piston  304 . 
     Each of the ultrasonic inducers  426 ,  427  produce the ultrasonic waves  428  that are directed into an interior of the cylinder  306  and then detected by a receiver  429 . Changes in the ultrasonic waves  428  may indicate the location of the piston  304  proximate to the ultra sonic inducer  426 ,  427 . As the piston  304  travels within the cylinder  306  between the cylinder rear  311  and the cylinder head  309 , the detected changes in the ultrasonic waves  428  indicate when the piston  304  reaches the travel limits in either the un-actuated position or the actuated position. Therefore, the detected changes in the ultrasonic waves  428  may be used to determine a position of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The ultrasonic waves detected by the receiver  429  may be passed to the ROV  121  and/or the surface unit  126  ( FIG. 1 ) to provide an indication of the location of the piston  304  and the ram  202 . The sensor S may also be operatively coupled to one or more ultrasonic inducers  426 ,  427  to provide an electrical and/or visual indication of the activation of a given ultrasonic inducer. The sensor S may pass the signal to various components, such as receiver  429 , for communicating a position of the piston  304 . A visual indicator, such as those provided herein, may also optionally be coupled to the monitoring system  103   e  to provide a visual indication of position upon activation by the monitoring system  103   e.    
       FIG. 4F  depicts an actuator  300   f  and a BOP monitoring system  103   f  as a laser sensor  432 . The laser sensor  432  may have one or more laser inducers  434  located proximate the end of the actuator  300   f . As shown, the laser inducers  434  are located proximate the cylinder rear  311 . The laser inducer  434  may direct a laser  436  through an aperture  438  of the cylinder  306 . 
     The laser  436  may engage a portion of the piston  304 . The laser  436  may have conventional range finding capabilities that may be used to determine the distance between the cylinder rear  311  and the piston  304  as the piston travels within the cylinder  306 . The piston  304  location as determined by the laser sensor  432  may be used to determine the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The location detected by the laser sensor  432  may be passed to the ROV  121  and/or the surface unit  126  ( FIG. 1 ) to provide an indication of the location of the piston  304  and the ram  202 . The sensor S may also be operatively coupled to the monitoring system  103   f  to provide an electrical and/or visual indication of the position detected by the laser  436 . The sensor S may pass the signal to various components for communicating a position of the piston  304 . A visual indicator, such as those provided herein, may also optionally be coupled to the monitoring system  103   f  to provide a visual indication of position upon activation by the monitoring system  103   f.    
       FIG. 4G  depicts an actuator  300   g  and a BOP monitoring system  103   g  as a linear magnetic sensor  440 . The linear magnetic sensor  440  may have a sensor magnet  442  coupled to the cylinder rear  311 . The sensor magnet  442  may couple to a linear sensor  444  that is placed into the cylinder  306  through an aperture  438  in the cylinder rear  311 . The linear sensor  444  may detect movement of a piston magnet  416  as the piston  304  moves. As shown, the piston  304  may have a cavity  446  for allowing the piston  304  to pass the linear sensor  444  without engaging the linear sensor  444 . 
     As the piston  304  travels within the cylinder  306  between the cylinder rear  311  and the cylinder head  309 , the linear sensor  444  detects the location of the piston magnet  416 . The piston magnet  416  location may be used to determine the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The location detected by the linear sensor  444  may be passed to the ROV  121  and/or the surface unit  126  ( FIG. 1 ) to provide an indication of the location of the piston  304  and the ram  202 . The sensor S may also be operatively coupled to the monitoring system  103   g  to provide an electrical and/or visual indication of the position detected by the linear sensor  444 . The sensor S may pass the signal to various components for communicating a position of the piston  304 . A visual indicator, such as those provided herein, may also optionally be coupled to the monitoring system  103   g  to provide a visual indication of position upon activation by the monitoring system  103   g.    
       FIG. 4H  depicts an actuator  300   h  and a BOP monitoring system  103   h  as a Hall Effect sensor  448 . The Hall Effect sensor  448  may have one or more sliding magnets  420  secured to the guide rod  422  located on the outside of the side  307  of the cylinder  306 . Each of the sliding magnets  420  may be secured to the guide rod  422  in a manner that allows the sliding magnet  420  to translate along the guide rod  422  in response to the movement of a piston magnet  416  on piston  304 . As the piston  304  travels within the cylinder  306  between the cylinder rear  311  and the cylinder head  309 , the piston magnet  416  translates the sliding magnet  420  proximate the piston  304 . 
     Proximity sensors  421  may be positioned on either side of sliding magnet  420  to detect the position of the sliding magnet. The magnet  420  may be detected by the proximity sensors  421  as the magnet approaches thereby indicating the position of the piston  304 . Therefore, the Hall Effect sensor  448  may provide a specific electrical and/or visual indication of the piston  304  and the rod  308  position or location. Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The location detected by the Hall Effect sensor  448  may be passed to the ROV  121  and/or the surface unit  126  ( FIG. 1 ) to provide an indication of the location of the piston  304  and the ram  202 . The sensor S may also be operatively coupled to the monitoring system  103   h  to provide an electrical and/or visual indication of the position detected by the proximity sensor  421 . The sensor S may pass the signal to various components for communicating a position of the Hall Effect sensor  448 . 
       FIG. 4I  depicts an actuator  300   i  and a BOP monitoring system  103   i  as a moving magnetic sensor  450 . The moving magnetic sensor  450  may have one or more magnetic indicators (or filings)  452  located within a transparent case  454 . The transparent case  454  may be, for example, a tube located on the outside of the side  307  of the cylinder  306 . Each of the magnetic indicators  452  may be secured within the transparent case  454  proximate the cylinder  306  in a manner that allows the magnetic indicator  452  to translate within the transparent case  454  in response to the movement of the piston magnet  416 . As shown in  FIG. 4I , the magnetic indicator  452  is a plurality of magnetic shavings. However, the magnetic indicator  452  may be any suitable indicator such as one or more magnetic ball(s) (as shown in  FIG. 4J ). 
     The transparent case  454  may have any suitable form for allowing the magnetic indicator  452  to travel. The transparent case  454  may be transparent to allow for visual inspection of the location of the magnetic indicator  452 , as the magnetic indicator  452  travels within the transparent case  454 . The magnetic indicator  452  may be used to provide a visual indication of the location of the piston  304  and the rod  308 . As the piston  304  travels within the cylinder  306  between the cylinder rear  311  and the cylinder head  309 , a piston magnet  416  on piston  304  translates the magnetic indicator  452  through the transparent case  454  to a position proximate the piston  304 . The magnetic indicator  452  location may be used to determine the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The sensor S may also be operatively coupled to the monitoring system  103   i  to provide an electrical and/or visual indication of the position detected by the magnetic indicator  452 . The sensor S may pass the signal to various components for communicating a position of the piston  304 . 
       FIG. 4J  depicts an actuator  300   j  with a BOP monitoring system  103   j  as another moving magnetic sensor  453 . The monitoring system  103   j  is similar to the monitoring system  103   i , except that the transparent case  454  as shown in  FIG. 4J  may be a transparent race (or tube) for receiving the magnetic indicator  453  and allowing it to translate therein. The magnetic sensor  453  may be, for example, a ball that rolls through the transparent race as the piston moves within the cylinder  306 . 
     As the piston  304  travels within the cylinder  306  between the cylinder head  309  and the rear  311  of the BOP  108 , the piston magnet  416  translates the magnetic indicator  453  proximate the piston  304 . The magnetic indicator  453  location within the transparent tube may be used to provide a visual indication of the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The magnetic indicator  453  location may be used to determine the location of the piston  304  and the rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. The sensor S may also be operatively coupled to the monitoring system  103   j  to provide an electrical and/or visual indication of the position detected by the magnetic indicator  453 . The sensor S may pass the signal to various components for communicating a position of the piston  304 . 
       FIGS. 4K-4N  depict various configurations of a pulley monitor  103   k,l,l ′.  FIGS. 4K-4M  depict longitudinal cross-sectional views of an actuator  300   k,l,l ′, and  FIG. 4N  depicts an end view thereof.  FIG. 4K  depicts an actuator  300   k  and a BOP monitoring system  103   k  as a gear drive sensor  456 . The gear drive sensor  456  may have a gear drive housing  458  coupled to the cylinder rear  311 . The gear drive housing  458  may have a cable (or flexible member)  460  that is placed into the cylinder  306  through an aperture  438  therein. The cable  460  may couple to the piston  304  and travel therewith as the piston  304  travels within the cylinder  306 . A pulley  469  may be provided to drive the gears  462  as the cable  460  moves with the piston  304 . 
     As the piston  304  moves from the un-actuated position to the actuated position, the cable  460  may be pulled by the piston  304 . The cable  460  movement may rotate one or more gears  462  located within the gear drive housing  458 . One of the gears  462  may couple to and/or rotate a first portion of a magnetic coupler  464  located within the gear drive housing  458 . The first portion of the magnetic coupler  464  may magnetically couple to a second portion of the magnetic coupler  466  located outside of the gear drive housing  458 . 
     The rotation of the second portion of the magnetic coupler  466  may be measured and used to determine the location of the piston  304  as it travels within the cylinder  306 . An indicator arrow  467  may be positioned on the magnetic coupler  466  and rotated therewith. The position of the indicator arrow  467  may be used as an electrical and/or visual indicator to indicate the position of the piston  304 . As shown in  FIG. 4N , the indicator arrow may rotate to a position along the second portion of the magnetic coupler  466 . The rotational position of the indicator arrow  467  may correlate to a position of the piston in cylinder  306 . 
     The gears  462  may be spring wound in order to retract the cable  460  when the piston  304  travels from the actuated position to the un-actuated position. The piston  304  location as visually indicated by the indicator arrow  467  may be used to determine the location of the piston  304  and rod  308 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
       FIG. 4L  depicts an actuator  300   l  with a BOP monitoring system  103   l  as a pulley drive. In the system  103   l  as shown in  FIG. 4L , the cable  460  wraps around a first pulley  469  and a second pulley  468  within the pulley housing  458 . Thus, as the piston  304  moves within the cylinder  306 , the pulley  468  is rotated. The pulley  468  may couple to the first portion of the magnetic coupler  464  located within the pulley housing  458 . The first portion of the magnetic coupler  464  may magnetically couple to the second portion of the magnetic coupler  466  located outside of the pulley housing  458 . 
     The rotation of the second portion of the magnetic coupler  466  may be measured and used to determine the location of the piston  304  and the rod  308  as it travels within the cylinder  306  in a similar manner as that described for  FIG. 4K . As also described with respect to  FIG. 4K , the indicator arrow  467  may be used to provide an electrical and/or visual indication of the piston  304 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
       FIG. 4M  depicts an actuator  300   l ′ with a BOP monitoring system  103   l ′ as a pulley drive. The actuator  300   l ′ is similar to the actuator  300   l , except that the pulley housing  458  and contents are rotated 90 degrees, and the pulley housing  458  is integral with the cylinder  306 . As indicated by  FIG. 4M , the visual indicators (or monitors) herein may be positioned at various locations about the cylinder  306  to facilitate viewing thereof. As also indicated by  FIG. 4M , the visual indicators (or monitors) may be positioned in housings integral with the cylinder  306  (or separate from as shown by  FIGS. 4K and 4L ). 
     The rotation of the second portion of the magnetic coupler  466  may be measured and used to determine the location of the piston  304  and the rod  308  as it travels within the cylinder  306  in a similar manner as that described for  FIG. 4K . As also described with respect to  FIG. 4K , the indicator arrow  467  may be used to provide a visual indication of the piston  304 . Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
     The movement of arrow  467  may be detected by a sensor S. The sensor S may also be operatively coupled to the monitoring system  103   k - m  to provide an electrical or visual indication of the position of the arrow  467 . The sensor S may pass the signal to various components for communicating a position of the piston  304 . 
       FIGS. 5A-5D  depict alternate schematic, cross-sectional views of an actuator  300   m - p  having various versions of a monitoring system  103   m - p  usable as the actuator  300  and BOP monitoring system  103  of  FIG. 3  and depicting the operation thereof. As shown in each of these figures, the piston  304  is slidably movable within the cylinder  306 . In these figures, for simplicity, the rod  308  is not shown. The monitoring systems  103   m - p  are each positionable about the cylinder  306  and have devices for detecting a position of the piston  304  therein. Each piston  304  is operatively connectable to a ram  202  (see  FIGS. 2 and 3 ) and, therefore, a position of the rams  202  (and/or components thereof) may also be determined. In each of these monitoring systems  103   m - p , a sensor S may also be operatively coupled to the monitoring system  103   m - p  to provide an electrical and/or visual indication of the detected position of the piston  304 . The sensor S may pass the signal to various components for communicating a position of the piston  304 . A visual indicator, such as those provided herein, may also optionally be coupled to the monitoring system  103   m - p  to provide a visual indication of position upon activation by the monitoring system. 
       FIG. 5A  depicts an actuator  300   m  and a BOP monitoring system  103   m  as a capacitive displacement sensor  506 . The capacitive displacement sensor  506  may flow a current  502  within the cylinder  306 . The current  502  may be sent into the cylinder  306  with one or more source electrodes  504  coupled to the cylinder rear  311 . 
     A sensor electrode  506  may detect the current after the current has engaged the piston  304 . Changes in the current detected by the sensor electrode  506  may be used to determine the distance of the piston  304  from the cylinder rear  311 . The piston  304  location may be used to determine the location of the piston  304  (and the rod  308  not shown). Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
       FIG. 5B  depicts an actuator  300   n  and a BOP monitoring system  103   n  as a sonar sensor  508 . The sonar sensor  508  may produce a sonic wave  510  within the cylinder  306 . The sonic wave  510  may be propagated into the cylinder  306  and reflected off of the piston  304 . The reflected sonic wave  510  may be detected by a receiver  512 . 
     Changes in the detected sonic wave  510  may be used to determine the distance of the piston  304  from the cylinder rear  311 . The piston  304  location may be used to determine the location of the piston  304  (and rod  308  not shown). Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
       FIG. 5C  depicts an actuator  300   o  and a BOP monitoring system  103   o  as one or more proximity sensor(s)  514 . The proximity sensor(s)  514  may be any suitable detection sensor that determines the location of the piston  304  within the cylinder  306 . For example, the proximity sensor  514  may be a mechanical sensor such as a button or a switch, an electrical sensor such as a strain gauge, a sonar sensor, and the like. The proximity sensor  514  may be coupled to, for example, the ROV  121  or surface unit  126 . 
     The proximity sensor(s)  514  may detect the location of the piston  304  when the piston  304  is in the actuated and/or un-actuated position. There may also be multiple proximity sensor(s)  514  along the cylinder  306  in order to give the location of the piston  304  as the piston  304  translates within the cylinder  306 . The piston  304  location may be used to determine the location of the piston  306  (and rod  308  not shown). Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
       FIG. 5D  depicts an actuator  300   p  and a BOP monitoring system  103   p  as a flow sensor  516 . The flow sensor  516  may be, for example, a totalizing mechanical flow meter configured to measure the flow into and/or out of the cylinder  306  as the piston  304  is extended and retracted. The flow sensor  516  may be coupled to a fluid source, such as a tank (not shown). Pumps, flowlines or other fluid devices may be provided to assist in manipulating the flow of fluid through the flow sensor  516 . 
     With the inner volume of the cylinder known, the hydraulic flow into the cylinder may be used to calculate the position of the piston  304  within the cylinder. Alternatively, when the piston  304  is retracted toward the un-actuated position, the mechanical flow meter may reset back to zero instead of measuring the outflow. The piston  304  location may be used to determine the location of the piston  304  (and rod  308  not shown). Thus, the location of the rams  202  (as shown in  FIG. 3 ) may also be determined. 
     Each of the monitors  103   a - p  depicted in  FIGS. 4A-4N, 5A-5D  may be used to indicate a position of the piston  304 . These monitors  103   a - p  may be coupled via a communication link (e.g.,  134  of  FIG. 1 ) to the ROV  121  and/or surface unit  126  for passing signals therebetween. Such signals may contain data that may indicate (or be analyzed to indicate) the position of the piston  304 . Some of the monitors  103   a - p  may provide visual indicators (e.g., monitors  103   b - c,i - l ), such as the flags  412  of  FIG. 4B , magnets  420  of  FIGS. 4C and 4H , magnetic indicators  452 ,  453  of  FIGS. 4I and 4J , that may be visually inspected by an operator, ROV, camera or other devices to determine a position of the piston. The visual indicators may also be provided with visual indicator sensors to electrically indicate a position of the sensors. Some of the monitors  103   a - p  may provide trigger sensors having electrical indicators (e.g., monitors  103   a,d - h,m - p ) that may send signals to the surface unit indicating a position of the piston. One or more cylinders  306  of a BOP  108  may be provided with one or more of the monitors  103   a - p  about various locations. 
       FIG. 6  is a flow chart depicting a method ( 600 ) for monitoring a blowout preventer. The method ( 600 ) involves positioning ( 680 ) the blowout preventer about a tubular, activating ( 682 ) at least one of the visual indicators of the monitor as the piston passes adjacent thereto, inspecting ( 684 ) the visual indicators, and sensing ( 686 ) a position of the piston with an electrical indicator. The inspecting may also involve manually viewing the visual indicators and/or sensing the visual indicators for activation. The method may also involve additional steps, such as passing data from the monitor to a surface unit. The steps may be performed in an order, and repeated as desired. 
     Blowout Preventer Monitor with Trigger Sensor 
       FIG. 7  is another view of the BOP  108 . This version includes a BOP housing  701  with multiple rams  202  ( FIG. 3 ) with corresponding actuators  300 . Each actuator  300  includes the cylinder  306  with an end cap (or ram door)  711  removable about an end thereof. An upper one of the end caps  711  has been replaced with a BOP monitor (or ram position indicator)  703 . In some cases, the BOP monitor  108  is a BOP monitoring system or a portion thereof. 
     The BOP monitor  703  may track the movement of a BOP ram  202  passing through the BOP  108  in the same way as shown in  FIGS. 2 and 3 . As the ram  202  moves to engage the tubular  104 , the BOP monitor  703  is activated to monitor movement thereof and/or to determine a position thereof. The BOP monitor  703  may be used to determine the displacement of the ram  202 , and thus its position in the BOP  108 . 
       FIG. 8  shows a portion of the BOP  108  depicting the actuator  300  including the piston  304  slidably positionable in the cylinder  306 . The end cap  711  ( FIG. 7 ) of the cylinder  306  has been removed and replaced with the BOP monitor  703 . The BOP monitor  703  is removably positionable about an exterior end of the cylinder  306  with a portion thereof positioned within the cylinder  306  and a portion positioned outside the cylinder  306 . 
     The BOP monitor  703  includes a monitor base  851 , an interior plate  868 , an exterior plate  866 , and a trigger sensor  857 . The monitor base  851  is removably positioned about the end of the cylinder  306 . The monitor base  851  may be, for example, threadedly disposed in the cylinder  306  or bolted thereto. The monitor base  851  may seal the cylinder  306  in the same manner as did the end cap  711  removed therefrom. 
     The interior plate  868  may be rotationally coupled along an inner surface of the monitor base  851 . The interior plate  868  may include a pulley wheel  869  with a cable  360  disposed about a perimeter thereof. The cable  360  may couple the piston  304  to the interior plate to translate movement therebetween. Movement of the piston  304  within the cylinder  306  may extend and retract the cable  360 . As the cable  360  extends and retracts, the interior plate  868  may rotate therewith. 
     Because the base  851  replaces the end cap (ram door)  711 , the exterior plate  866  and interior plate  868  may be connected to the base  851  on either side thereof. The exterior plate  866  may be disposed outside of the end cap (ram door)  711  of ram cylinder  306  of the BOP  108 . Interior plate  868  may be disposed inside of the end cap (ram door)  711 . The exterior plate  866  and interior plate  868  may rotate about the base  851  as the ram  202  ( FIG. 2 or 3 ) of the BOP  108  moves therein. 
     The exterior and interior plates  866 ,  868  may be positioned on opposite sides of the base  851  and offset axially relative to each other by some distance. The exterior plate  866  and the interior plate  868  may be fixed axially such that they do not move in the axial direction and such that they may be free to independently rotate about a centerline axis Z. The exterior plate  866  and the interior plate  868  may be, for example, metal (e.g., steel) plates that are circular in shape. However, the exterior and interior plates  866 ,  868  may take another shape in other embodiments. The axial centerline Z of the exterior plate  866  and the interior plate  868  may be aligned as represented in  FIG. 8  by the single axial centerline Z. 
     The exterior plate  866  may be rotationally coupled along an exterior surface of the monitor base  851 . Magnets  864   a - d  may be matingly positioned about the interior plate  868  and the exterior plate  866  for magnetic interaction therebetween. The magnets  864   a,c  of the exterior plate  866  and magnets  864   b,d  of the interior plate  868  are magnetically engagable through the monitor base  851  to provide a magnetic coupling therebetween. The magnetic coupling may be used to transfer rotation of the interior plate  868  through monitor base  851  to the exterior plate  866  as indicated by the dual rotational arrows. Magnets  864   a - d  may be any magnet capable of transferring rotation between the exterior plate  866  and the interior plate  868 , such as N50/52 magnets or other functionally equivalent types of magnets. 
     The monitor base  851  may be used to fluidly isolate the trigger sensor  857  on an exterior of the cylinder  306 . The interior plate  868  is coupled to the piston  304  within the cylinder  306 . The exterior plate  866  is outside the cylinder and magnetically coupled to the interior plate  868  via magnets  864   a - d . This configuration may be used to permit rotation of the exterior plate  866  outside the cylinder  306  (and BOP  108 ) using a mechanically detached coupling, such as magnets  864   a - d  to translate movement from inside the cylinder  306  to an exterior of the cylinder  306 . 
       FIG. 9A  shows another view of the BOP monitor  703  depicting the trigger sensor  857  therein. As shown  FIGS. 8 and 9 , the trigger sensor  857  is disposed about the exterior plate  866  and the monitor base  851 . To depict the trigger sensor  857 , the exterior plate  866  and the monitor base  851  have been shown in dashed line. The trigger sensor  857  includes a sensor base  859  with a rod  861  extending therefrom, a trigger (or loading device)  865  with a plunger (or push block)  867  extending therefrom, and a bearing  855 . The sensor base  859  is positioned in a sensor pocket  863  extending into the exterior surface of the monitor base  851 . The rod  861  extends from the sensor base  859  and into a trigger pocket  869  in the exterior plate  866 . The bearing  855  is positioned in the trigger pocket  869  and has a hole to receive a tip of the sensor rod  861  therein. The bearing  855  may have an exterior ring positionable in the exterior plate  866  engagable by the plunger  867 , and an inner ring to receive a tip of the rod  861  therein. The trigger  865  is positioned on the exterior plate  866  with the plunger  867  engagable with the bearing  855 . 
     The trigger sensor  857  as depicted may be a strain rosette or strain gauge. The trigger sensor  857  detects movement of the exterior plate  866  to provide a signal measurable to determine a position of the piston and, therefore, the rams. Trigger sensor  857  is coupled to exterior plate  866  at its centerpoint about axis Z. The trigger sensor  857  has a known X and Y direction. A resultant directional vector V may be determined based on a magnitude and direction of strain detected by the trigger sensor  857  in the X and Y direction. The load/force from trigger  865  is assumed to be about constant. The force produced by trigger  865  is transferred to the sensor base  859  through the plunger  867 , bearing  855 , and the sensor rod  861 . 
     The sensor rod  861  deflects in the direction of the force produced by the trigger  867  and this deflection is measured in the sensor base  859  via strain gage methods. A change in direction of the force also changes the direction that the sensor rod  861  deflects, which is measurable by the sensor base  859  as the exterior plate  866  rotates. This change in direction may be used to determine a vector angle of the load which may be used to determine an angle of the exterior plate  866 . Given the known geometry of the BOP monitor  703 , the angle of the exterior plate  866  may be used to determine a ram position. 
     Trigger sensor  857  may be, for example, a strain gauge capable of measuring strain along multiple axes, such as three axes, as schematically illustrated in  FIG. 9B . The 0° strain gauge measures strain along the Y-axis, the 90° measures strain along the X-axis, and the 45° measures a combination of the two and is used to increase accuracy. The combination of the three 0°, 90°, 45° allows for tracking the strain—magnitude and direction—as exterior plate  866  rotates due to any rotation of interior plate  868 . Other configurations and angles may be used. 
     As also shown, an accelerometer (or other additional sensor) A may optionally be provided. Outside forces (e.g., forces other than those associated with the magnets  864   a - d ), may impact interior plate  868 , causing vibration or shock loads in exterior plate  866  that may be sensed by trigger sensor  857 . For example, gravity may cause a downward pull on the exterior plate  866 , and vibration may affect directional load from the exterior plate  866  in any direction. Failure to consider these forces may lead to inaccurate determinations of exterior plate  866  rotation and thus ram displacement and position. 
     To compensate or correct for potential errors that may be caused by the outside forces (e.g., gravity and vibration) that may impact exterior plate  866  and, in turn, be sensed by the trigger sensor  857 , various forces may be considered. Data from the accelerometer A may be paired with the trigger sensor  857  readings to give accurate rotation position by factoring out gravity and vibration experienced through the accelerometer A. The measurements of the trigger sensor  857  and the accelerometer A may be transferred to a controller, surface unit, or other device (see, e.g.,  126 ,  128  of  FIG. 1 ) for collecting and/or analyzing data. 
     Movement of the piston  304  extends and retracts the cable  360 . Movement of the cable  360  rotates the interior plate  868 . Magnets  864   b,d  of the interior plate are coupled to the magnets  864   a,c  to translate movement of the interior plate  868  to the exterior plate  866 . The tip of sensor rod  861  extends into the bearing  855  in the exterior plate  866 . Plunger  867  of trigger  865  pushes the bearing  855  and the tip of the rod  861  such that the rod  861  is offset from axis Z along an offset axis Z′. 
     Bending/deflection of the sensor rod  861  provides measurements detectable by the sensor base  859 . The sensor base  859  may be coupled to the BOP  108 , controllers  126 ,  128 , and or other devices to transfer sensed measurements thereto. The trigger sensor  857  detects movement of the exterior and interior plates  866 ,  868  to provide a signal measurement to determine a direction vector which may be used to determine a position of the piston. 
       FIGS. 10A and 10B  show various views of the BOP monitor  703 .  FIG. 10A  shows an exterior end view of the BOP monitor  703 .  FIG. 10B  shows an interior end view of the BOP monitor  703 . 
     As shown in  FIG. 10A , the BOP monitor  703  is depicted as a circular member connectable to the cylinder  306 , for example, by bolts. The exterior plate  866  also has a visual indicator in the form of dial (or arrow)  871  rotatable with the exterior plate  866 . The dial  871  may be similar to the dial  467  of  FIGS. 4K-4N . The dial  871  and exterior plate  866  as shown are rotatable between an open and closed position as indicated by the arrow. Markers  881   a,b  may be provided to depict open and closed positions, respectively, along the exterior face of BOP monitor  703 . 
       FIG. 10A  also depicts another view of the trigger sensor  857 . The trigger sensor  857  is depicted in the exterior plate  866  with the rod  861  extending into the trigger pocket  869 . The trigger  865 , plunger  867 , and bearing  855  are depicted in the exterior plate adjacent to the rod  861 . As shown in this view, the trigger  865  is a flat spring or beam  882  extending between fixed supports  885 . The spring receivingly engages the plunger  867  and urges the plunger  867  toward rod  861  as indicated by the arrow. The spring  882  may include a fixed bar extending between the supports and one prong extending from each support parallel to the fixed bar. The fixed bar keeps the prongs aligned. The plunger  867  is positioned midway between the two prongs and is urged by the prongs to apply a force to the bearing  855  and rod  861  to push/deflect the rod  861  off center from axis Z ( FIG. 8 ). As also shown in this view, the magnets  864   a,b  and  864   c,d  are aligned about exterior plate  866  and interior plate  868  ( FIGS. 8 and 9A ). The magnets  864   a - d  are the same distance from the axis Z. 
     As shown in  FIG. 10B , the interior plate  868  is positioned adjacent to the base  851  and includes a pulley (or wheel)  873  and a separate cover  875 . The wheel  873  has an exterior surface positionable adjacent the monitor base  851  and a perimeter to receive the cable  360  thereabout. The cover  875  is disposable about an inner surface of the pulley  873 , and has a hole  870  therethrough for passing the cable  360  therethrough to connect with piston  304  ( FIG. 8 ). 
       FIG. 10C  shows another version of the BOP monitor  703 ′. This version is the same as shown in  FIG. 10A , except that a modified exterior plate  866 ′ and sensor  865 ′ are provided. The exterior plate  866 ′ is disposable about an exterior cover  891  and a spacer  890 . The exterior plate  866 ′ has the visual indicator  871  thereon and has teeth  889  along a periphery thereof engagable with the sensor  865 ′. While teeth  889  are shown in this example, other detectable features, such as alternating light and dark bands along a periphery of the exterior plate  866 ′ may be used. 
     The sensor  865 ′ extends through the spacer  890  and to the teeth  889  on the exterior plate  866 ′. The sensor  865 ′ may detect the teeth  889  as they rotate past, thereby indicating a rotational position of the exterior plate  866 ′. A known angle between the teeth  889  and a size of the rotating exterior plate  866 ′ may be used to determine linear travel of the rams. 
       FIGS. 11A, 11B, and 11C  show partial cross-sectional, exterior exploded, and interior exploded views, respectively, of the BOP monitor  703 . These views show the BOP monitor  703  in an assembled and a disassembled configuration. These views also show the components of  FIGS. 8, 9, and 10A , plus additional optional components, such as seals  879 , a spring  880 , dial cover  887 , and additional connectors (e.g., bolts)  877 . 
     Seals  879  may be used to prevent fluid leakage through the BOP monitor  703 . Spring  880  may be a rotational spring that urges the interior plate  868  into a refracted position to retract the cable  360  from the piston  304  and to keep the cable  360  taught ( FIG. 8 ). Dial cover  887  may be a clear cover to protect the exterior plate  866  and dial  871  and/or seal the sensor  865  in the exterior cover  891 . Various connectors, such as bolts may be provided between various portions of the BOP sensor  703  to secure such portions in place. The sensor base  859  with rod  861  thereon may be adjustably mounted in the monitor base  851  by bolts. 
     As also shown in  FIG. 11B , the exterior plate  866  may mount to a bearing  893  which is mounted to an adapter  892  which bolts to the monitor base  851 . The exterior plate  866  is free to rotate around the sensor rod  861  using bearing  893 . Dial (or visual indicator)  871  is positioned on exterior plate  866 . As also shown in  FIG. 11C , the monitor base  851  is provided with an interior pocket  883  and a shaft  885  on an interior side thereof to receive the interior plate  868 . 
       FIG. 11D  also shows an alternate configuration of the BOP monitor  703 ″ which is similar to the BOP monitor  703  of  FIGS. 11A and 11B , except that the exterior plate  866  includes two exterior covers  866   a , a dial plate  866   b , and a spacer  866   c″.    
     FIGS.  12 A 1 ,  12 A 2 ,  12 B 1 ,  12 B 2 ,  13 A, and  13 B show schematic views of another version of the BOP monitor  703 ′″. FIGS.  12 A 1  and  12 A 2  show views of the BOP Monitor  703 ′″ in a zero or initial position. FIGS.  12 B 1  and  12 B 2  show views of the BOP monitor  703 ′″ rotated α degrees (e.g., about 45 degrees clockwise). The BOP monitor  703 ′″ of FIGS.  12 A 2  and  12 B 2  are the same as the BOP monitor  703  of  FIG. 10A , except that the magnets have been moved to an offset position. FIGS.  12 A 1  and  12 B 1  are schematic views of the BOP monitor  703 ′″ of FIGS.  12 A 2  and  12 B 2 .  FIG. 13A  shows the BOP monitor of FIG.  12 A 1  taken along lines  13 A- 13 A.  FIG. 13B  shows the BOP monitor of FIG.  12 A 2  taken along lines  13 B- 13 B. 
     As shown in these views, the magnets  864   a - d  are in an offset position about interior plate  868  and exterior plate  866  to translate motion therebetween. One or more pairs of magnets, such as magnets  864   a - d  as shown, may be magnetically coupled to translate rotation between the exterior plate  866  and interior plate  868 . 
     As with the magnets depicted in the aligned position of  FIG. 10A , magnets  864   a,c  on exterior plate  866  enable exterior plate  866  of  FIGS. 12A and 12B  to remain aligned with interior plate  868  such that the axial centerlines Z of plates  866 ,  868  coincide. Likewise, magnets  864   b,d  on interior plate  868  enable interior plate  868  to remain aligned with exterior plate  868  such that the axial centerlines Z of the plates  866 , 868  coincide. Opposing magnets  864   a,c  on exterior plate  868  and interior plate  866  closest to each other, due to their proximity, are attracted to one another. 
     In the offset configuration of FIGS.  12 A 1 - 12 B 2 , magnets  864   a,c  on exterior plate  866  are radially offset from centerline Z. In the exemplary embodiment, magnets  864   b,d  on interior plate  868  may also be radially offset from centerline Z to different degrees. In other words, the radial distance Da between magnet  864   a  and centerline Z is different than the radial distance Dc between magnet  864   c  and centerline Z. In the exemplary embodiment, magnets  864   b,c  are also radially offset from centerline Z to different degrees. In other words, the radial distance between magnet  864   b  and centerline Z is different than the radial distance between magnet  864   d  and centerline Z. 
     The offset of the magnets  864   a - d  creates a side force between exterior plate  866  and the sensor rod  861  (or intermediate components transfer the side force to sensor rod  861 ). The side force is created as the offset magnets  864   a,b  try to pull each other into axial alignment. Similarly magnets  864   c,d  try to pull each other into axial alignment. The magnets  864   a - d  are offset in such a way as to cause the pull force between each set of magnets to be in the same direction. The rotation axis of exterior plate  866  and interior plate  868  and centerline of sensor rod  861  are aligned with centerline Z when the magnets are in the offset position. A hole, pocket or intermediate device in exterior plate  866  is positioned to contact sensor rod  861 . 
     The pull force from the grouping of offset magnets acts to move exterior plate  866  away from centerline Z. The established contact with sensor rod  861  prevents exterior plate  866  from moving away from centerline Z. Exterior plate  866  will rotate in conjunction with interior plate  868  due to the magnetic attraction between  864   a,b  and  864   c,d . The rotation of the plates also causes the side force exerted onto sensor rod  861  to rotate which can be sensed and measured by sensor base  859 . The sensed strain may then be used to determine the rotation of plate  868  and in turn the displacement and position of the ram. The relative positions of magnets  864   a,c  and magnets  864   b,d  causes a net side force thru exterior plate  866  onto sensor rod  861  shown in  FIG. 12A  to be in the downward direction. This side force direction will rotate with the rotation of plates  866  &amp;  868 . 
     As also demonstrated by  FIGS. 13A and 13B , trigger sensor  857  is coupled to monitor base  851 . However various sensors may be used, such that the mounting may be on the exterior cover  891 , dial cover  887 , or spacer  890 . 
       FIG. 14  depicts a method  1400  of monitoring a position of a ram of a BOP, such as the BOPs provided herein. The method involves  1491 —operatively connecting a monitor comprising a monitor base, an interior plate, an exterior plate, and a trigger sensor to the blowout preventer by operatively connecting the monitor base to the cylinder, an interior plate about an interior surface of the monitor base, and an exterior plate about an exterior surface of the monitor base,  1493 —rotating the interior plate with the rams via a cable,  1495 —rotating the exterior plate with the interior plate via the magnets, and  1496 —determining a position of the rams by sensing rotation of the exterior plate with the trigger sensor. 
     The trigger sensor comprises a sensor base positionable in the monitor base and a rod extending from the sensor base into the exterior plate, and the determining  1496  may involve detecting a position of the exterior plate by deflecting the rod and measuring a position of the rod with the sensor base during the rotating. The trigger sensor may include a sensor base positionable in the monitor base and a rod extending from the sensor base into the exterior plate, and the determining  1496  may involve detecting a position of the exterior plate by detecting keys along a periphery of the exterior plate with the trigger sensor. 
     The method may also involve additional steps, such as  1497 —collecting (or passing) data from the trigger sensor,  1498 —passing data from the trigger sensor to a surface unit,  1499 —adjusting the blowout preventer based on the determining. The steps may be performed in an order, and repeated as desired. 
     It will be appreciated by those skilled in the art that the techniques disclosed herein can be implemented for automated/autonomous applications via software configured with algorithms to perform the desired functions. These aspects can be implemented by programming one or more suitable general-purpose computers having appropriate hardware. The programming may be accomplished through the use of one or more program storage devices readable by the processor(s) and encoding one or more programs of instructions executable by the computer for performing the operations described herein. The program storage device may take the form of, e.g., one or more floppy disks; a CD ROM or other optical disk; a read-only memory chip (ROM); and other forms of the kind well known in the art or subsequently developed. The program of instructions may be “object code,” i.e., in binary form that is executable more-or-less directly by the computer; in “source code” that requires compilation or interpretation before execution; or in some intermediate form such as partially compiled code. The precise forms of the program storage device and of the encoding of instructions are immaterial here. Aspects of the invention may also be configured to perform the described functions (via appropriate hardware/software) solely on site and/or remotely controlled via an extended communication (e.g., wireless, internet, satellite, etc.) network. 
     While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible. For example, one or more monitors (with one or more sensors, pairs of magnets, and/or other components) may be positioned about one or more cylinders of a blowout preventer. Also, the monitoring devices described herein may detect positions of the piston  304  (and other portions of the ram  202 ) in an unactuated position, an actuated position, and/or all other positions therebetween. Various portions of the sensors, monitors, BOPs, and other devices herein may be combined. 
     Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.