System and method for position monitoring using ultrasonic sensor

A subsea blowout preventer stack comprising:

• a blowout preventer;
• a subsea hydraulic accumulator configured to provide hydraulic fluid to power the blowout preventer, the accumulator comprising an internal volume with a gas side and a fluid side separated by a piston moveable within the accumulator internal volume and an end cap with a recess formed within the internal volume of the accumulator;
• and
• a measurement system comprising:
• a sensor module positioned within the recess of the end cap and comprising:
• an ultrasonic transducer facing the piston and configured to transmit an ultrasonic signal through a fluid medium in the accumulator internal volume toward a surface of the piston;
• a pressure sensor configured to measure the pressure of the fluid medium;
• a temperature sensor configured to measure the temperature of the fluid medium;
• and
• a controller positioned within the recess of the end cap and coupled to the sensor module, capable of providing hardware and software functions to measure transit time of the ultrasonic signal through the accumulator to determine the location of the movable element within the accumulator;
• and
• wherein the location of the piston within the accumulator is indicative of remaining volume of the fluid medium within the internal volume of the accumulator.