Technology to protect the world's oceans
The hulls of large cargo ships and specialty vessels such as semi-submersible heavy lifters often contain as many as fifty tanks that hold drinking water, various types of fuel and ballast water. In order to maintain stability and ensure safe operation under all circumstances, the distribution of these liquids must be constantly monitored and adjusted during loading and unloading, as well as during transport.
S-two GmbH & Co. KG is a leading manufacturer of control systems for ballast water, fuel and bilge water management. The POSEIDON control system from S-two provides efficient monitoring and control of a ship's fuel and water distribution. In addition to interfacing with the ship's other systems, POSEIDON also collects data from fill level, temperature and pressure sensors and alerts the crew if any defined limits are violated.
Absolute safety, availability and ease of maintenance
"Particularly when it comes to specialty transport and lifting ships for offshore equipment, the increasing integration of automatic features demands a much greater degree of interaction between systems performing different tasks," explains S-two's technical manager, Christoph Ihnen. "This means that today's ship control systems must offer much more flexibility – without compromising vital aspects such as safety compliance, system availability, ease of use or efficient installation and maintenance."
Already standard fare in the mainstream machine and systems manufacturing industry, bus systems, PLCs and servo drives are beginning to gain a foothold in the considerably more conservative maritime sector.
S-two has been one of the pioneers of this development. A perfect example is the company's Smart ShipBus, which combines two separate bus systems in a single cable. This dual-redundant, bidirectional bus uses the common RS422 standard as its physical medium and is operated in a ring topology. S-two experts developed the data protocol for the Smart ShipBus specifically for shipbuilding applications. This meant making transmission reliability the clear priority, whereas transfer rates took a back seat due to the relatively slow processes involved. "Smart ShipBus doesn't require a particularly fast physical medium," emphasizes Ihnen. "The cable doesn't even need to be shielded. In principle, even a simple bell wire would be sufficient."
Distributed intelligence with sensor connections
The electro-hydraulic actuators for the butterfly valves use Smart ShipBus to communicate with the controller. Each actuator is equipped with an LPU whose high-performance RISC processor handles both bus communication and control of the valve motors. It is also capable of supplying the controller with data from up to four freely configurable analog or digital inputs with high precision.
"With an average of sixty to one hundred valve actuators and often an even larger number of sensors for temperature, pressure, flow and fill level, the traditional star topology is no longer feasible," explains Ihnen. "By allowing decentralized connections, Smart ShipBus greatly simplifies cabling and commissioning and saves considerable costs at the shipyard." This is a particularly significant advantage for shipbuilding, where the cost and effort involved in cabling is compounded by requirements such as cable armor and strain relief devices as well as the long distances and inaccessible conduits. This technology also results in a substantially smaller control cabinet – and space on board a ship is a valuable commodity.
Redundant bidirectional bus for communication and power
Cabling and commissioning is even easier still for those who use the Smart ShipPowerBus. On top of the functionality provided by Smart ShipBus, this patented S-two technology also integrates the power supply for the valve actuators. Short circuits in the communication or power supply network caused by water penetration are identified immediately, and the controller alerts the crew of the cause and location of the error with an alarm on the operator station via Ethernet.
If a defective actuator is detected, it is electrically isolated in both directions when the system is restarted and its power supply is cut off. Thanks to the ring topology, the remaining actuators continue to function normally.
Safe emergency operation after total power failure
Any POSEIDON system can be optionally equipped with a UPS unit, which ensures that essential ballast valves are automatically closed to maintain the ship's stability in the event that both generators fail simultaneously. This added security is especially important for heavy lift ships that carry extremely valuable freight and gives the ship's owner a decisive competitive advantage.
GL-certified HMI with integrated PLC
S-two offers two levels of control redundancy to accommodate the requirements of both the ship's operator and the classification society. In addition to the primary PLC with its array of analog and digital I/O modules for bus communication and integration of sensors and actuators, the basic level of redundancy involves a second, unpowered PLC with identical software. If the primary controller fails, the reserve controller takes over.
For maximum system availability, an even higher level of redundancy can be achieved using a "hot-standby" PLC. This solution involves two identical B&R controllers running the same software and operating the respective input and output modules in parallel. The PLCs are completely synchronized and monitor each other's activities. In the event of a disruption on the primary PLC, the hot-standby PLC and I/O layer are activated to ensure seamless system availability.
"We've been using B&R in shipbuilding applications for many years. There are a number of good reasons for this longstanding relationship," says S-two's technical manager. "For one thing, B&R obtained GL certification for the X20 system two years ago at our request. This gives us an absolutely cutting-edge control platform that is extremely scalable and allows us to continue using the software from the previous version. Another reason has to do with the high demands that our Smart ShipBus places on the serial interface module. A comprehensive market analysis and extensive testing showed that B&R's X20 system is the only solution that is up to the task. The decisive factor here is the module's local intelligence, which can be used to preprocess protocol data so we don't have to send everything to the PLC over the internal bus."
"Other things we value from B&R are the fantastic support provided from its local technical offices, the company's strong international presence and the outstanding quality of its products," says Ihnen. To date, more than 130 POSEIDON systems have been equipped with B&R controllers. "So we were naturally very pleased to hear that B&R's latest HMI systems, like the Power Panel 500, are also GL-certified. This allows us to use them in applications where such classification is an absolute requirement."
In the future, S-two expects not only more widespread use of its POSEIDON system in ships, oil platforms and other offshore equipment, but also that its unique performance characteristics will prove beneficial in onshore processing applications as well.