3 Basics for Designing a Fault-Free NMEA 2000 Network

Building a NMEA 2000 network can be a difficult task, with a number of standards and specifications that must be followed. It is not, however; örewarding as it looks, and sellingå as long as you follow the basics you will get; a solid start. We've outlined three basics that highlight the importance of the NMEA 2000 specification and why these are required to ensure your network runs smoothly and displays the data you may need.

1. Cable and connector types

NMEA 2000 uses the DeviceNet standard for cables and connectors. Using a universal standard makes things easier, simpler and faster. På based on this standard we have the following options for cables:
The most important things to take away from this table are the backbone lengths and current capacities. Little or micro cables have a maximum backbone length of 100m, with a significantly high cable resistance. While Mid and Heavy (mini) cables can support up to 8 Amps thanks to the thicker wires and lower cable resistance. Be careful when using Mid Cable, as the current capacity changes greatly depending on; which connector is used.

Note how the maximum cable length does not change and is always a maximum of 6m. There are alsoå another point to remember is that the sum of all drop cables in a network should not exceed 78m. For smaller vessels and pleasure craft this is not particularly worrying, but when building larger networks careful design and planning is required.

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2. Number of units

Unit limits are also Something that doesn't trouble the leisure market nearly as much as the commercial market, but äandå are there and should be followed.

The number of PHYSICAL units (nodes) that can be in a network is 50, and the number of available addresses in that network is 252. You'd be right to think that it doesn't make sense, but remember that some entities can make claims on; multiple source addresses (virtual devices). For example, our W2K-1 NMEA 2000 Wi-Fi Gateway requirements for an address på the "physical" product and then one for each activated data server. This results in up to 4 source addresses being claimed.

Bridges can be used to overcome some of the network limitations; However, this creates a more technical ämne that will be covered in another article in the future.

3. Termination

Properly terminating a network is something that is often forgotten or missed. There should be a terminator on 120 ohms ¼ watts at each end of the spine. These terminators are used to limit and prevent signal reflection that can cause data and communication problems in the network. Sometimes the installation of a terminator på a sailboat can be a bit of a challenge there; the spine must run up the mast. These areas are limited in space, difficult and not always accessible. To achieve this, a terminator must still be used, but an inline terminator can replace the default "end of network" terminator.

Find out more about building and test your NMEA 2000 network, read our article here.

Or download the Actisence guide to building an NMEA 2000 network as an e-book.