Modbus Integration

A Navtech Radar with the SafeGuard functionality enabled can act as a Modbus master or a Modbus slave device.

In addition to a single register that presents the alarm state of the six SafeGuard detection & reporting zones, there are further registers which allow a connected device to report various aspects of it's health.

The key aspects of the radar’s Modbus configuration are shown in the screenshot of the radar’s web user interface below. These settings apply, irrespective of whether the SafeGuard functionality is enabled in the radar.

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From this page, the following settings are available:

Modbus Mode: This is the data output mode.

None: Disabled

Master: The radar will poll other devices that are operating as a slave.

Slave: The radar acts as a server and makes alarm data available to the Modbus master.

Relay: The radar will output area alarms via a Relay unit instead of using Modbus.

Modbus Address: This is the IP Address of the slave and is only available to be used if the radar is acting as a Master. In slave mode, the address is the same as the radar.

Port: This is the port used by Modbus in order to connect to the slave.

Health Offset: This is the register offset used by Modbus. If this value is set to 0, the radar’s health data will be presented in the lowest numbered Modbus holding registers.

Heartbeat Period (Hz): The heartbeat is in the form of an incrementing count. The heartbeat update rate can be selected via Vertex to be either 1Hz, 4Hz, 8Hz or 16Hz. The default value is 4Hz, which we generally recommend.

This allows customers with systems that require a faster rate-of-response to check the heartbeat more frequently.

Heartbeat Watchdog: Modbus Watchdog provides an additional level of connectivity robustness as it can be used to detect end-to-end connection problems over large networks, such as half-open connections.  This feature checks holding register 40002 for a changing heartbeat value provided by a connected device. If the radar does not see a changing value in this register within a definable timeout (1-10sec) then the radar will drop the TCP/socket connection and attempt to re-establish it. This watchdog functionality can be turned on or off via the checkbox.

Heartbeat Fail Timeout (Sec): When this function is enabled, the radar will periodically check the value of Modbus holding register 40002. If the remotely supplied heartbeat value doesn’t change within the specified Heartbeat Fail Timeout period, the radar will drop the TCP socket connection used for Modbus (severing any half-open connections, for example) before restarting the radar's Modbus TCP connection.

The six SafeGuard alarm states are presented by the value in a specific Modbus holding register. This register can be configured through the radar’s web user interface as shown below:

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The Watchdog Counter is an incrementing number - attached devices can monitor the change in this to identify that the Modbus communication link is correct and operational.

Radar Health

Radar health is presented as a set of registers containing current status values, and a register declaring overall health status for each of the parameters. Each health status is declared as three mutually-exclusive bits, each bit representing whether the parameter is healthy, warning or unhealthy.

Radar health (firmware v3.1.0.415 or earlier)

Radar health status flags are defined as follows:

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The next three registers, as shown in the screenshot below, present:

• Operating Temperature (in Degrees C)

• Rotation Rate in mHz

• Packet Rate, which is the number of azimuths of data presented per second

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The screenshot of a very simple Modbus listener, above, shows how the radar health is presented in the lowest registers, and how the health status ‘bits’ are mapped within a single register for radar firmware 3.0.0.92-3.1.0.415

Radar health (firmware v3.1.0.416 and later)

From firmware v3.1.0.416 onwards the radar health status has been extended to include CPU load. The radar health status flags have been reorganised to allow for future expansion.

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The next four registers, as shown in the screenshot below, present:

• Operating Temperature (in Degrees C)

• Rotation Rate in mHz

• Packet Rate, which is the number of azimuths of data presented per second.

• CPU Load, as a percentage

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The screenshot of a very simple Modbus listener, above, shows how the radar health is presented in the lowest registers, and how the health status ‘bits’ are mapped within a single register, for radar firmware firmware v3.1.0.416 and later