Type and Instance settings for a NMEA2000 network

Understanding Type and Instance on an NMEA 2000 Network

What is NMEA 2000?

NMEA 2000 (N2K) is a standardized communication network used in marine electronics. It allows different devices—such as sensors, engines, and fuel tank monitors—to share data efficiently over a single backbone cable.

Each device on an NMEA 2000 network needs to be properly identified so the system can understand and use its data correctly. This is where Type and Instance settings become essential.

Why Are Type and Instance Settings Important?

When multiple sensors or devices of the same kind exist on a network, they must be correctly labeled to prevent confusion. If two fuel tank level sensors send data without distinct identification, your display might show incorrect readings or fail to differentiate between tanks. The same applies to engine monitoring sensors—incorrect settings could lead to misinterpreted engine data, making diagnostics difficult or even misleading.

By correctly setting Type and Instance, you ensure:

• Accurate data reporting

• Clear identification of each device

• Reliable system performance

What is Type?

Type defines what a device does. It tells other devices how to interpret its data.

Examples:

• Fuel Tank Sensor (Type 70) – Measures fuel level.

• Engine Temperature Sensor (Type 130) – Monitors engine temperature.

• Oil Pressure Sensor (Type 131) – Reports oil pressure readings.

What is Instance?

Instance identifies multiple devices of the same Type. This prevents confusion when more than one similar device is present.

Examples:

• Fuel Tank Sensor 1 (Type 70, Instance 0) – Corresponds to the port-side fuel tank.

• Fuel Tank Sensor 2 (Type 70, Instance 1) – Corresponds to the starboard-side fuel tank.

• Engine Temperature Sensor 1 (Type 130, Instance 0) – Monitors the port engine.

• Engine Temperature Sensor 2 (Type 130, Instance 1) – Monitors the starboard engine.

Without unique Instance numbers, devices may send mixed signals, leading to incorrect readings.

Multiple Gauges Displaying the Same Information

NMEA 2000 allows multiple gauges or displays to show the same data from a single sensor. This is useful when you want fuel level, engine temperature, or oil pressure readings available in different locations on your vessel.

How it works:

• A fuel tank sensor (Type 70, Instance 0) sends data to the NMEA 2000 network.

• Any display unit on the network can read this data and show the fuel level.

• You can have a gauge at the helm and another in the engine room, both showing the same tank level.

• The same applies to engine temperature and oil pressure sensors—data is available to multiple displays without needing duplicate sensors.

This setup ensures:

• Consistent data across all locations

• No need for separate sensors for each gauge

• Reduced wiring complexity

How to Set Type and Instance

Some devices allow you to adjust the Instance number through a chartplotter or setup tool.  Wema devices require a NMEA2000 setup tool and can not be set through a chartplotter.  You can also specify your type and instance setting when ordering from Wema UK and we will preset them before shipping.

When designing your NMEA2000 network:

1. List all devices – Note each device and its Type.

2. Identify duplicates – Find devices that share a Type.

3. Assign unique Instances – Use different numbers for similar devices.

4. Preset each device – Request device to be preset when ordering or use a Wema Setup Tool.

5. Verify functionality – Confirm that each device reports correctly.

Best Practices for Setting Instances

• Assign Instance 0 to the primary device (e.g., port-side tank or engine).

• Assign Instance 1 to the secondary device (e.g., starboard-side tank or engine).

• Label each device physically to match its network Instance number.

• Create a network map for future reference, ensuring correct assignments.

Common Issues Caused by Incorrect Type and Instance Settings

• Duplicate Instances – Two sensors of the same Type have the same Instance number, leading to unpredictable readings.

• Incorrect Type Assignment – A fuel tank sensor is incorrectly set as an oil pressure sensor for example, resulting in unusable data.

• Confusing Readouts – Data from the starboard fuel tank appears as the port tank because Instance numbers are swapped.

Why It Matters

A well-organized NMEA 2000 network avoids data conflicts. You get accurate readings from sensors, clear engine data, and reliable navigation information.

Does your setup have multiple devices of the same Type? If so, check their Instance numbers. This is the most common reason for NMEA2K networks not working correctly.