Thursday, 6 December 2012

NMEA2000 Networked Instruments

Over the last year we have noticed a growing trend of customers enquiring about networked instruments. It seems that people are now exploring what is possible with a NMEA 2000 network and how it offers a relatively simple way of connecting multiple instruments, chartplotters and sensors together to share data.

Traditionally instruments were connected directly to their sensors or were supplied with NMEA0183 ports, enabling connection to another device such as a repeater. The single talker and multiple listener serial ASCII format of the NMEA 0183 protocol is fine for connecting an instrument to a repeater or linking a GPS to an autopilot but is not suitable for duplex communication and is limited by both speed and power. Also non standardisation of connectors, with most instruments offering bare wire connections, scared many off from exploring its full capabilities.

The National Marine Electronics Association (NMEA) recognised the need for a higher speed duplex network and developed NMEA 2000. The system is an implementation of the automotive CAN bus system that was developed by Bosch in the 1980s. The NMEA 2000 method of connection, in its basic form, consists of a powered backbone made up by a series of T pieces terminated at either end with termination resistors.  Instruments and sensors are connected to the backbone T pieces via drop cables.

The major instrument manufacturers adopted this system and now offer chartplotters, instruments and sensors that can connect directly to the NMEA 2000 backbone and share data. Also, the standardisation of the connection hardware has simplified networking and enables the end user to link multiple instruments and sensors together no matter which brand. Some manufacturers such as Raymarine and Simrad developed their own protocol (Seatalkng and Simnet) but offer low cost converters to enable NMEA 2000 integration.

The January 2013 edition of PBO features a very interesting article on networked instruments which compares some of the current models from the major manufacturers.  In this article the B&G Triton receives the best on test award.




Raymarine i70 (Force 4 part number 220196) To connect to a NMEA 2000 network you will need a Seatalkng to DeviceNet adaptor cable (Force 4 part number 230141)

You tube video of how to build a network

Seaman Leigh

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