Submersible Pressure Transducers Used in Marine Applications

The marine sector uses pressure transducers that are designed to operate reliably in harsh conditions. Pressure transducers are used in flood alarms, reservoirs, storage tanks, hydraulic systems and in cooling systems. Marine sensors are designed to be resistant to anything from mechanical shocks, to hydraulic spikes (originating from pumps and valves), to high temperatures. Pressure transducers allow all of these applications to run smoothly at all times.

For pressure transducers to operate reliably under extreme conditions, they must be designed well, with well-considered electronics and diaphragms. Modern devices use a combination of ASIC electronics and CVD-based technology to deliver powerful performance, with a high accuracy and optimal hysteresis behavior. These sensors are manufactured for operations over millions of cycles and are designed for submersion.

Pressure transducers are sensors that convert pressure changes in a fluid (i.e. a gas or liquid) into an electrical signal. As the signal they deliver can be continuous, pressure transducers feed constant readouts to relevant control systems. This allows smart control systems to be set up where decreasing pressure levels can set off a series of alarms, which are tailored to the readout, with the most serious resulting in system shutdown.

Marine pressure transducers can be used in any part of a ship, as they are specifically designed to operate under harsh conditions (for example, at high temperatures/pressures, and in liquid interfaces). Transducers can improve efficiency and performance in systems such as gearboxes and propulsion units, or in management and the measurement of temperatures, clutch pressure or oil systems.

Pressure transducers are designed to be resistant to the vibrations that occur on ships. Despite being highly accurate and sensitive systems, they can still provide accurate readings even in situations involving large amounts of motion. Transducers consist of multiple components and are composed of many different materials. Even in sub-optimal operating conditions, they can still deliver uncorrupted outputs. Modern transducer manufacturers have designed systems which can guarantee great performance levels whilst at sea.

Three technologies are key to the exceptional performance of modern transducers. These technologies are CVD (chemical vapor deposition) technology, sputtered thin film technology and ASIC (application specific integrated circuits) electronics packaging. The combination of these electronic and mechanical advancements have resulted in a growing appetite for their use in the marine sector.

Chemical Vapor Deposition (CVD)

CVD is a high-specification method of manufacturing pressure transducers. CVD allows accurate devices with good hysteresis behavior to be produced in a compact form. The CVD process occurs via an economical batch process, which involves the deposition of polysilicon on a stainless steel surface, followed by chemical milling of the strain gauge patterns.

Following the milling, the wafer is then cut into individual sensor beams that are mounted onto a stainless steel summing diaphragm and pressure port, via laser welding. The wafers are connected to electronics that carry out signal amplification and conditioning.

CVD provides sensor manufacturers to economically mass-produce accurate and robust pressure sensors.

Sputtered Thin Film Technology

In order to measure pressure, transducers possess a thin sealed sensing diaphragm that is in contact with the media being measured. When the diaphragm is displaced, the strain gauge is flexed (either via tension or compression) which generates an electrical signal proportional to the displacement. The sensors output travels via on-board electronics, with the entire system compactly contained within stainless steel housing.

Sputtered thin film technology, an established manufacturing method for the production of integrated electronic circuits, was established thirty years ago. The process involves bombarding a solid material with energized particles, resulting in the sputtering of atoms. The sputtered atoms are then deposited onto a sensing substrate in a controlled electronic pattern.

Using sputtered thin film technology creates a sensitive and rugged sensor that operates while in direct contact with the majority of fluids, such as oils and gases. This means these sensors can be used in a huge variety of applications.

The application of the sputtered thin film layer during manufacture results in a sensitive, robust sensor that is suitable for direct contact with almost all liquids, oils and gases, offering the flexibility of use that has proved to be one of the great strengths of pressure transducers.

ASIC

The development of advanced electronics packaging been key in creating custom pressure sensors for the marine industries. Modern pressure transducers frequently use integral electronic signal conditioning, and this is made possible only with advanced ASIC technology.

ASIC allows the function and performance of individual transducers to be fine-tuned for different applications. In a similar way to CVD, the use of ASIC technology also reduces manufacturing costs, which is making pressure sensors even more prevalent in the marine sector.

Gems Sensors and Controls produce a wide range of robust and versatile pressure sensors using CVD. These include the capacitive Gems 5000 Series transducer, which is resistant to seawater corrosion with its duplex stainless steel housing. The 5000 Series has been shown to be highly useful in on-board applications for low-pressure sensing; such as the gauging of large but shallow tanks. Another sensor of note is the 2600 Series, which is a submersible sensor rated at IP65. This sensor provides stable and accurate measurements that can be used in several custom enclosures.

The impact of combining an advanced electronics system with state-of-the-art pressure sensors results in some powerful statistics. Pressure responses are possible at less than 1 msec, and the accuracy of the sensor does not drift over time. This excellent performance is retained over a huge number of cycles (greater than 100 million) and provides useful data for shipboard systems at an economical price, with no need for maintenance.

These breakthroughs in sensor and transducer technologies mean that answers to specific problems encountered by marine engineers can be accessed in standard units, meaning that custom solutions are no longer required. The increasing popularity of marine pressure inducers has led to greater knowledge-transfer among marine manufacturers, allowing them to design systems which meet the needs and requirements of the marine sector at large.

This information has been sourced, reviewed and adapted from materials provided by Gems Sensors and Controls.

For more information on this source, please visit Gems Sensors and Controls.

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