Seawater Corrosion-Resistant LVDT Ensures Accurate Control of
"Christmas Tree" Chokes Used in Sub Sea Applications

Pennsauken, NJ, March 31, 2009…

In subsea applications, the term "christmas tree" refers to an assembly of valves, spools and fittings for an oil well, which, in formation, resemble a decorated tree. The function of a "christmas tree" is to prevent the oil or gas release from an oil well, while directing the flow of fluids from the well. Valves on the Christmas tree are called chokes and, in subsea applications, are remotely controlled either by hydraulic or electric actuators. Position feedback is required for monitoring and controlling the choke status.

In subsea applications, the environment poses several performance criteria for the feedback sensors including operation in high pressures and resistance to chemically hostile seawater at depths to 12,000 ft. There is also a reliability requirement of 20 years minimum operating lifetime. Reliability is of critically important because the cost of replacing subsea hardware is extremely high.

Addressing this criteria, Macro Sensors designed a seawater corrosion-resistant, high-pressure, spring-loaded LVDT for use in a 5,000 psi pressure-balanced, oil-filled container. Designed from 316SS and Inconel 625 for pressure and corrosion resistance, the high reliability of the LVDT assembly ensures continued operation for many years, even if the device is fully exposed to seawater. A key element of the LVDT design is its zero leakage pressure sealing, verified by helium mass spectrometer leak testing.

The LVDT also offers extraordinary repeatability, regardless of offsets due to pressure and/or temperature, which is of paramount importance to ensure that when the chokes are nearly closed, flow is entirely shut off. Failure to completely close the choke could result in an environmental disaster.

Recognizing that LVDTs are inherently high-reliability devices, a Macro Sensors developed compatible 4-20ma loop-powered electronics, with high-reliability to meet the 20-year lifetime requirement. A 4-20mA I/O also minimizes any noise over long transmission lines. Offsets can be easily made in the data acquisition system on the platform above. To minimize the likelihood of premature failure, electronics were subjected to many different ESS tests after burn-in to eliminate "infant mortality". Macro Sensors' LVDTs also resolve the problem of getting a signal back to the surface, even in great water depths.

For more information on High Pressure and Chemically Resistant LVDTs and other custom LVDT units from Macro Sensors, please contact the factory at postionsensors@macrosensors.com or refer to the web site at http://www.macrosensors.com/custom_lvdts.html

About Macro Sensors

Macro Sensors manufactures an extensive line of linear and rotary sensors for position measurement and feedback in a variety of industrial applications including factory automation, motion control systems, metal fabricating, automotive assembly as well as power plants, gas/steam turbines. Incorporated in 1994, the Company offers more than 200 years of cumulative design and manufacturing experience by its key staff in serving its OEM and end-user international customer base. For more information on our products, visit our web site at www.macrosensors.com. On June 1, 2005, Macro Sensors was acquired by AST, manufacturer of state-of-the-art Micro-Electro- Mechanical- Structures (MEMS) based pressure sensors, transducers, and transmitters. Common applications of AST sensor products are in industrial OEM, hydraulic systems, fuel cells, medical gases, HVAC/R, refrigeration, oil & gas exploration/production, and off-road vehicles. For more information on AST products and technology, visit the AST website at http://www.astsensors.com.