A new wave of technology
Sensors are a key tool used by marine engineers to manage the performance of a wide range of equipment. Today, sophisticated sensor technology is typically easy to install and use, improving the performance and service life of the components and systems it controls and monitors, and also reducing operating and maintenance costs significantly.
The fact that so much is at stake for marine operators has driven the development of a range of tools and practices to prevent premature failure and its consequences. A considerable amount of bad publicity can be generated by severe failures, whether caused by the unscheduled docking for repairs of a container ship or the malfunction of ventilation fans on passenger ships, and so marine sensors have been continually refined and upgraded to achieve a consistent and efficient management of essential machinery throughout its lifetime.
Building in shock and vibration resistance is a must, with the designers needing to appreciate the most extreme operating circumstances. Space is always at a premium on marine vessels, which inevitably leads to heat dissipation problems when machinery is operating. This problem can be compounded in locations where the ambient temperature is extremely low, with control systems subject to extreme thermal cycling. Ensuring that electronic equipment stays within specific operating temperatures will maintain reliability and prolong working life, often by many years. Continuous innovation in cooling techniques has meant that electronics solutions have become viable in ever more arduous environments.
In marine applications, the measurement of pressure, level and flow in applications such as fuel tanks, hydraulic system reservoirs, flood alarm systems, bilges, potable water storage tanks and cooling systems requires marine sensors that are built for long and reliable service. Thankfully, the designers of today’s components have succeeded in delivering sensors that can withstand everything from high pressure hydraulic spikes originating from pumps and valves to extremes of temperature, mechanical shock and vibration. Before looking at exactly how this has been achieved, let’s consider precisely what these devices are and how they are used.
A commonly used sensor is the pressure transducer. A pressure transducer converts pressure, typically that of fluid or gas, into an electrical signal. By delivering a continuous output of electrical signals that correspond to the precise pressure status, transducers offer a range of options for the control system. For example, a gradual decrease in pressure might trigger a series of escalating alarm signals, allowing appropriate action to be taken before the ultimate level is reached, triggering an automatic shutdown.
In marine applications, pressure transducers are ship-wide and can function under harsh conditions, including liquids that are turbulent liquids and/or contain foreign material. Pressure transducers are also used to handle liquid interfaces, high temperature environments and high-pressure fluids. In equipment such as propulsion units and gear boxes, the monitoring and management of oil, temperature and clutch pressure with transducers can make a major difference to performance and overall efficiency.
The fact that today’s pressure, level and flow devices can cope with constant shipboard vibration, yet continue to give accurate readings, is impressive, particularly when you consider the sensitivity of these components and the accuracy of the measurements they can provide. The technological advances recently applied to pressure transducers have enabled their use in vessels from commercial to military to become so widespread that solutions to specific problems sought by shipboard engineers are now often found in standard units, negating the need for custom solutions. The popularity of pressure transducers in marine applications has, in turn, made their designers ever more familiar with shipboard requirements and ever more able to provide devices that meet the challenges of life at sea.
Key to the ability of pressure transducers to work reliably and accurately under such a wide range of marine operating conditions is the way in which sensor diaphragms and electronics packages are constructed. Current devices combine the latest chemical technology with ASIC electronics to form powerful instruments. It is the successful combination of these mechanical and electronic technologies that has enabled pressure transducers to offer such reliable and accurate performance. These compact devices can provide high levels of accuracy, with excellent hysteresis characteristics, over millions of cycles, and can be effectively manufactured in submersible form.
One particular factor that has significantly increased the potential for pressure transducers to be tailored to the needs of the marine sector has been the development of integral electronic signal conditioning incorporating advanced ASIC technology. With ASIC, the performance and functionality of each transducer can be tuned to meet the specific requirements of individual customers. The benefits of ASIC technology have also included reductions in manufacturing costs, which can only lead to an even greater presence of pressure sensors in marine applications.
Gems Sensors and Controls manufactures a range of resilient pressure transducers for marine applications. For example, the Gems 5000 Series transducer is cased in duplex stainless steel, providing to the corrosive effect of sea water, and has provided an efficient solution on board ship in low pressure applications, such as gauging large but shallow tanks.
By combining sensitive pressure sensing elements with sophisticated electronics, responses to changes in pressure can take 1ms or less, with almost zero drift over time. Such performance can be maintained over long periods; transducers can now offer an operating life in excess of 100 million cycles, protecting shipboard systems at a low cost and with little or no maintenance.
The best of today’s level measurement components are packaged in protective housings that maintain reliable operation even if, for example, there is solid matter in the bilge water. Such switches can provide point level sensing in inaccessible areas of tanks, and can be supplied with vulcanised cables, offering level switches with an ingress protection rating of IP67 for use as submersible sensors.
High durability can be achieved in marine flow sensors, which are designed for low pressure drop and to enable detection to be carried out where liquids are being handled in high volumes, such as lubrication, cooling or process applications. To enable switch actuation at the desired flow rate, flow paddles can be trimmed during installation; this allows the paddle of the switch to pivot and move out of the liquid path as flow increases, keeping pressure drop to a minimum regardless of pipe size.
With the current crop of pressure, level and flow sensors, the potential to reduce maintenance both planned and unplanned is considerable. By surveying the current options when specifying pressure monitoring devices and keeping a keen eye on the developing technology, engineers can tailor systems with sensor components that help maintain marine systems at peak efficiency.
