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History and trends: CAN goes on (and under) the sea

CAN networks are used in maritime electronics since a long time. There are different standardized applications based on CANopen and J1939 (known as NMEA 2000). Currently, CiA started to specify a dual-mode redundancy concept suitable for all three CAN protocol generations.

(Source: Adobe Stock)

The complete article is published in the June issue of the CAN Newsletter magazine 2022. This is just an excerpt.

Already, mid of the 90ties, MTU (Germany) reported on the 2nd international CAN Conference (iCC) in London about CAN networking in ship automation systems. Dr. Olaf Schnelle presented the MCS-5 decentralized automation system, which was on duty for about 20 years. In the meantime, it is substituted by the Ethernet-based MCS-6 monitoring and control system. In midterm, all MCS-5 systems will be converted to the MCS-6 controllers. MTU’s engine control system (ECS) is still connected to the MCS-6 host controller by means of a CAN interface and discrete I/O lines. The CAN interface is redundant as required in marine applications.

Another early adopter of CAN networking in maritime electronics was Kongsberg (Norway). Jointly with Ixxat (now part of HMS networks, Sweden), the Norwegian company developed ship automation systems based on CANopen. Prof. Dr. Konrad Etschberger (Ixxat) presented it on the iCC 2000. This technical solution went into the CiA 307 specification for electronics in ships and vessels. In the meantime, the document was withdrawn. The significant parts of the CiA 307 document, especially the CANopen redundancy, has been moved into the CiA 302-6 document not more dedicated and limited to marine applications.

A typical product, implementing the profile, is the segment control unit (SCU) by Kongsberg, which can manage multiple CANopen network segments. Optionally, the SCU provides an Ethernet-Powerlink interface running a CANopen-based application layer. The K-Chief 600 propulsion control system is another CAN-connected product by the Norwegian container vessel supplier. The Finnish company Wärtsilä is a manufacturer of marine engines with embedded CAN communication.

As an example, the Wärtsilä 46F medium-speed marine engines with power outputs up to 11250 kW are available in 6-cylinder to 9-cylinder in-line configurations. For condition-based maintenance, the engine provides continuous temperature monitoring of the bearings and the exhaust gas as well as real-time data monitoring of the engine performance. The 46F is equipped with a scalable embedded control system based on five hardware modules controlling engine safety functions, instrumentation, speed control, overall engine functionality, and the electronic fuel injection.

The NMEA 2000 application profile for maritime electronics is especially used in navigation systems (Source: Adobe Stock)

The architecture is based on CAN for communication between the modules and Ethernet connection to the external automation systems. The system also internally implements redundancy on selected systems and components. Recently, Wärtsilä introduced the 46TS-DF engine, which is designed with a focus on efficiency, environmental performance, and fuel flexibility. In gas fuel mode, the engine has the highest efficiency thus far achieved in the medium-speed engine market, said the manufacturer.

Dual-mode redundancy also for CAN FD and CAN XL

The CANopen redundancy concept specified in CiA 307 respectively CiA 302-6 is not suitable for CAN FD and CAN XL. Therefore, Kongsberg and Microcontrol started to develop a generic dual-mode redundancy solution for CAN-based interfaces independent of the used CAN data link layer protocol. It should suit Classical CAN, CAN FD, and CAN XL. It is currently under development in the CiA Interest Group high availability. This dual-mode redundancy approach is based on two independent CAN interfaces each comprising a CAN controller and a CAN high-speed transceiver.

There is also a finite state automaton specified, which manages the selection and eventually the swapping of the active and the passive interface. The data frames are always transmitted on both segments, but on the receiving side there is only one line active. For redundant use, some connectors with their recommended pinning are given in the CiA 106 Technical Report. This document dedicated for all CAN-based higher-layer protocols and CAN generations derives from the CiA 303-1 connector recommendations formerly specified for use with CANopen.

NMEA 2000: The J1939-based network for navigation

End of the 90ties, the US-based National Marine Electronics Association (NMEA) developed the successor of the 4,8-kbit/s NMEA 0183 serial communication link. This approach was based on the CAN lower layers and the J1939 application layer i.e. using Classical CAN communication with 29-bit CAN-Identifiers. It was named NMEA 2000 and internationally standardized in IEC 61162-3 running at 250 kbit/s. The multi-drop network is not completely interoperable with all features of the J1939 specifications, but can co-exist in J1939 networks. The cabling is similar to Devicenet specifications. The fast packet transport protocol is limited to 223 byte and does not require a segment confirmation. CAN in Automation (CiA) is observing the standardization activities of the NMEA association. According to the organization, there are no plans to migrate to CAN FD or CAN XL.

The CAN-based higher-layer protocol and application profile for maritime electronics is especially used in navigation systems. NMEA 2000 products need to be certified by the non-profit association. Examples of NMEA 2000 devices include GPS receivers, navigation and engine instruments, nautical chart plotters, wind instruments as well as depth sounders. Some companies such as Furuno, Ray-marine, and Simrad offer other connectors as specified in NMEA 2000. They sell their products not under the brand NMEA 2000, but use the NMEA 2000 parameter groups (PG).

NMEA 2000 product suppliers

Of course, there are several providers of CAN-supporting hardware, software, interfaces, and services for the marine industry. The CiA member company Wärtsilä Lyngso Marine (former Søren T. Lyngsø in Denmark) belongs to the Wärtsilä group and develops electronics for the marine applications. The product range includes automation devices as well as communication and navigation systems. CANopen, J1939, and NMEA 2000 higher-layer protocols can be supported.

Warwick Control Technologies (UK) provides the J1939-based protocol stack kit supporting NMEA 2000. It comprises the protocol stack in C source-code, an STM32 development board, an NMEA-certified reference design CAN driver for STM32 micro-controllers, the X-Analyser tool, and the Leaf Light USB dongle by Kvaser. The C source-code incorporates such J1939 features as address claim, fast packet protocol, BAM (broadcast announce message), connection management data transfer etc. The X-Analyser analysis and simulation tool supports NMEA 2000, J1939, CANopen, and CAN FD. For J1939, it allows to view parameter group number (PGN) packets, compare them to the raw CAN data, and to decode the packets into fields and signals. It also looks for harness/connector problems in the CAN signal. The analyzer supports all Kvaser CAN interfaces, as well as the Picoscope 2206b by Pyco Technology.

The wireless CAN bridge by Kvaser enables CAN communication in situations where wired CAN connection is challenging e.g. in marine applications (Source: Kvaser)

Beside of CAN interfaces, further hardware, and tools, Kvaser offers the recent configuration-free Kvaser Air Bridge Light HS M12. The wireless CAN bridge with dust and water-resistant M12 connectors can replace CAN cables in marine and other extreme environments. Comprising a pre-configured pair of wireless units with integrated antennas and rugged housings, the bridge exchanges raw CAN data between two networks when a wired CAN connection is challenging. The transmission range is up to 70 m, with a maximum data rate of 1 200 messages per second and a packet latency of 4,8 ms. Although this model incorporates two 5-pin M12 connectors with NMEA 2000 compatible pinning, the bridge is not an NMEA 2000-certified device.

The MLI-E 12/1200 Lithium-Ion battery from Mastervolt comes in a water proof plastic case, recharges in less than an hour, and deep-cycles 5000 times, which is up to 10 times longer than for lead-acid batteries. For integration in mobile and maritime power systems, NMEA 2000 and CANopen protocols are supported. The battery is protected against overcharging, deep discharging, and overheating and comes with an integrated electronic safety switch. The MLI-E is provided with integrated battery monitoring, including information about state of charge and time remaining.

For integration in maritime power systems the NMEA 2000 protocol is supported (Source: Mastervolt)

Connecting measurement equipment under the sea

CAN networks are used not only above the water surface. Under the sea, diverse sub-sea measurement equipment and control systems can be interconnected via CAN. For instance, the off-shore platforms for oil production are linked to sub-sea trees (nicknamed Christmas trees) comprising redundant controllers, different sensors, valves, and other equipment. These devices are located on the ocean ground in depths up to several hundreds of meters and are connected by means of CANopen networks. Such devices (also known as SIIS level-2 devices) comply to the CiA 443 CANopen profile, which was developed and is maintained by CiA in cooperation with the SIIS (Subsea Instrumentation Interface Standardization) group. The SIIS level-1 specifies discrete analog interfaces and the SIIS level-3 defines Ethernet interfaces.

The devices are controlled by an application manager, which is not specified in the CiA 443. Often, two manager entities are integrated into the network providing NMT (network management) “flying” manager functionality as specified in CiA 302-2. The virtual device concept of the CiA 443 profile enables a SIIS level-2 device to provide a sub-layered network or serial links. Thus, it acts as a gateway and provides proxies for the connected functional elements (e.g. different sensors).

The off-shore platforms for oil production are linked to sub-sea CANopen networks comprising redundant controllers, different sensors, valves, and other equipment (Source: Adobe Stock)

This means, SIIS level-1 devices can be easily integrated into SIIS level-2 networks. Of course, the sub-layered network may also comply with CiA 443. Two different physical layers are specified. Besides the low-power, fault-tolerant transceivers (compliant to ISO 11898-3) optionally high-speed transceivers (compliant to ISO 11898-2) are allowed. The default bit rate is 50 kbit/s and the bit-rate of 125 kbit/s is required as well. The SIIS group organizes plugfests, where the interoperability of CiA 443 compliant devices can be proven.

CAN in underwater vehicles

There is a growing demand for underwater vehicles. Several thousand meters below the surface, oil companies are prospecting for new deposits and deep-sea mining companies are looking for valuable mineral resources. The thousands of kilometers of pipelines and submarine cables need a regular maintenance. Additionally, the marine scientists would like to be able to use robust underwater exploration vehicles to survey large areas of the ocean floor.

If you would like to read the full article, you can download it free of charge or you download the entire magazine.

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Publish date
2022-06-27
Company

CAN Newsletter June 2022

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