The basics of building and testing your NMEA 2000 network

What is NMEA?
NMEA stands for National Marine Electronics Association. In a nutshell, they are a non-profit organization whose mission is to improve data communication between manufacturers of marine electronics. Read more about www.nmea.org

What is NMEA 2000?
NMEA 2000 is an open standard designed by NMEA to help them to achieve fulfills its mission by standardizing the messaging and connectivity systems used by entities in the marine industry. There is a common misconception that the term "open standard" means freely available when it actually means that the standard is available to purchase at a reasonable cost from their website. It is important to remember that NMEA is not for profit (NFP) and the standards create an important source of income as well; that they can continue to exist.

If you want complete peace of mind when building your NMEA 2000 network, you should use NMEA 2000 certified devices. Such devices have met all NMEA requirements and have received full certification. 

What are the benefits of NMEA 2000?
The simple the connection makes a NMEA 2000 network easy to set up.

• NMEA 2000 networks are reliable. They are self-configuring and no installation is required, meaning you can easily add or remove compatible equipment without having to restart the network.
• To unlike NMEA 0183, having different transfer rates is not a problem with NMEA 2000 network.
• NMEA 2000 network allows up to 50 different compatible devices to connect to each other.
• You don't need to replace your entire NMEA 0183 network when converting to NMEA 2000. You can easily connect to the new the network while maintaining for currently installed NMEA 0183 devices with a NMEA 2000 Gateway such as NGW-1.

What are the minimum requirements for that NMEA 2000 - network?
When you build your NMEA 2000 network there are some minimum requirements;

1. An insertion point for protected power (for example an Actisense A2K-MPT-2 connected to a krad battery source)
2. NMEA 2000 certified devices plus cables and connectors to build the network
3. Termination resistance

Actisense Starter Kits provide everything you need to create a basic NMEA 2000 network from the ground up.

Actisense's enticing network also provides; a "plug and play" network. However, it is important to note that SBN networks cannot be expanded.

Physical layer
The network connections (cables, tees, etc.) make up what is called NMEA 2000 'Physical Layer' and has been adopted by NMEA from the DeviceNet standard, a proven robust network solution that already used by vehicles and agriculture. industries (among others). DeviceNet uses a standard for wire sizes and wire colors that keep NMEA 2000 networks simple, and DeviceNet standard connectors allow quick and easy "plug & play" networking.

Backbone
The body of a NMEA 2000 network is known as the "backbone". All NMEA 2000 devices must be connected to the backbone via a T-Piece, this is known as an "instrument case". Each end of the backbone must be properly terminated with a 120 Ohm resistor. These resistors are connected in parallel and therefore provide 60 Ohm termination resistance across the entire network.

Cable – What are the correct cable sizes for a NMEA 2000 network?
The three different sizes of NMEA 2000 certified, DeviceNet standard cables are "micro", "mid" and "mini".
Micro – the smallest size på cables used for NMEA 2000 networks. Can be used to form the backbone for smaller installations as well as instrument drops.
Mid – an intermediate size of cables used only to install a NMEA 2000 trunk. more suitable for larger NMEA 2000 installations.
Mini – the largest cable size. Again, for use only to install a NMEA 2000 stem. A popular solution for larger NMEA 2000 installations.

The Actisense A2K series includes several options of pre-made lengths of micro-cable with over-molded, waterproof (IP 67 when mated), gold-plated connectors.
100 meter rolls of bulk cable, A2K-BULK-100M, also availableå available. When used with Actisense field-matched connectors, this provides a complete solution for custom lengths of NMEA 2000 certified cable. Multi-matched connectors will be explained in the "Connections" section.
The maximum body and instrument drop length for each cable type can be found in the "Network Limitations" section.

< strong>Connections – Are all NMEA 2000 connectors the same?
The DeviceNet standard allows for simple "plug & play" connection with screw connections that make installation quick and easy. The wire connections to each pin på the connectors have been defined in the NMEA 2000 specification, making the installation standard across NMEA 2000 installations. See the diagrams below for the rear view of the predefined NMEA 2000 pinouts.

As previously mentioned, devices connect to NMEA 2000 network via a NMEA 2000-certified T-Piece. Actisense A2K t-pieces (A2K-T-MFF) have been designed to that units can be easily connected even when the t-piece remains first at a bulkhead. The gold-plated screw connections make Actisense t-pieces durable and ensure they will last the lifetime of any NMEA 2000 installation.
In the area where up to four device connections are required can Actisense four-way tee (A2K-4WT) is used to drastically speed up installation time instead of using four individual tees.
Actisense Field Fit Connectors (A2K-FFC ) is available in both male and female options as well as a right-angled version for both cable types, perfect for installing NMEA 2000 cables in tight corners or around curves.

How to operate a NMEA 2000 nä twerk

Support with A2K-MPT-2:
The Actisense Micro power tee has a double pair of power cables, one for each side of the tee. Both pairs must be connected to a 12/24 volt power supply (via circuit panel) so that the electrical load can be distributed evenly.
When using 24V systems, a warning must be installed on The network needs to ensure that anyone who installs new devices is aware of it. This is due to that the NMEA 2000 specification does not officially support 24V but this level; of power saving can be used if installed devices can support it. All Actisense devices support 24V power supply.

Power with A2K-SBN-1 / SBN-2:
Power cord for the Small Boat Network is molded into the shell of a 4-way/8-way T-piece to prevent water ingress. Power is available to all 4/8 ports when the pair of blank wires are connected to a 12V or 24V power supply.

< strong>Support with Quick Network Block (QNB-1):

The Actisense Quick Network Block (QNB-1) provides a versatile and easy-to-install solution for all NMEA 2000 networks , which uses high-quality NMEA 2000 barrier tape connections. With bushings mounted on; QNB-1, it allows custom cable lengths and cable mixing, which means QNB can be implemented with Raymarine STNG cables for example.

QNB-1 splits the power supply with separate insurance on both sides, which enables longer networks with insulation on due to the ATO insurances. The second version (QNB-1-PMW), comes with 6 x M12 standard female (micro) connectors, allowing plug and play with drop cables.

You will hear from Learn common phrases used when discussing NMEA 2000 networks. Så here's what they mean:

• Backbone: The main cable trunk that runs through the bar to form the network. Tees are connected along the network for devices to connect to.
• Drop Cable: The length of the the cable that connects a NMEA 20000 device to the backbone network. It is important to note that the maximum length of a drop cable according to the NMEA 2000 standard is 6m.
• PGN: Stands for "Parameter Group Number". The messages used by NMEA 2000 devices to share information.

How do I test and diagnose my NMEA network?

Test current flow and termination resistance
Ideally the current should which is supplied to the network is tested at 2 points; the insertion point and the ends of the network.
Power reduction points should be tested to determine how much current is actually supplied to the network. All devices that do not have an external power source receive power from the mains, so there must be enough current to power all connected instruments.
The current should never exceed 14V and never fall below 9V. With network devices that use part of the supplied current and impedance from cables that also; lowers the voltage, it is important to know that the voltage at the end of each backbone is sufficient.
Temporarily remove a termination resistor from the end of the network and use a voltmeter to measure över the NET-S and NET-C pins. The measured value should be at least 9V.
When testing the resistance on; The network is the acquired value 60 ohms. This test can be performed by turning off the network and placing a DMM across the NET-H and NET-L pins. If 120 ohms is measured, only one termination resistor is installed. A second resistor must be installed in the opposite end of the network to the one already present.
If 40 ohms is observed, there are 3 termination resistors installed on the the network så 1 must be removed. If it is not obvious where the third resistor is, check if there are any devices on the network with termination resistors installed and make sure they are switched off. Network devices with termination resistors installed do not achieve NMEA 2000 certification because this practice can cause confusion in the network.

Further testing
About the problem remains after verifying that both the street cleaning and termination resistance is good, further testing is required: A common technique used to examine a network is to divide the network into sections by moving the terminator: Disconnect one half of the backbone and move the terminating resistor to the new, temporary End of the network.
If the problem persists, you have limited it to the half of the network that is still networked and active. If the problem persists, it is in the half of the network that has been disconnected.
Continue to perform this halving method until you can narrow it down to a single device, if possible.
Don't forget to move the termination resistor each time to Make sure the network is properly terminated. When the problem has subsided, try replacing the tees or cables with ones known to be good.
If field-matching connectors have been used, check the wire connections inside to make sure they are correct and properly secured på location.
If possible, check that the cables inside the device are properly and securely terminated, and be sure to observe antistatic precautions if the internal electronics are exposed. It is always best to check that this is ok with the device manufacturer before performing this step to ensure you are not voiding any warranty.
If a problem still persists, now you know there is a problem with the device and it's time to contact the manufacturer of it device.
For a complete guide to setting up your NMEA 2000 network and using Actisense products, download our NMEA 2000 eBook.