Blowout preventer monitor with trigger sensor and method of using same

A monitoring system for a wellbore penetrating a subterranean formation, the system comprising:

• a blowout preventer positionable about the wellbore, the blowout preventer comprising:
• a housing, at least one ram slidably positionable in the housing to form a seal about the wellbore, and an actuator comprising a cylinder with a piston slidably movable therein, the piston operatively connectable with the at least one ram and movable therewith, a monitor operatively connectable with the blowout preventer, comprising:
• 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 positioned 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 at least one ram may be determined.