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TT400 Wireless HART TM – Operation, Maintenance and Instruction Manual
VIII
the network that requested services to it, as well as manages the routes between the devices on the
mesh network.
Specifically, about the joining process of a Wireless HART device to the network, the Network
Manager validates the Network ID and the Join Key attributes which are configured in the
Wireless HART Gateway and Wireless HART devices.
The Network ID identifies a Wireless HART network in unique way. It is an unsigned integer attribute
and must be configured on the Wireless HART Gateway and all Wireless HART devices. Considering
a Wireless HART network installed in a plant, the permitted values for the Network ID ranges from 0
(hex 0x0000) to 32767 (0x7FFF hexadecimal).
The Join Key is a security key used to encrypt joining requests from Wireless HART devices that
receive the advertisement with the Network Id identical to theirs. It may be single or each
Wireless HART device may be configured with an individual Join Key. In the first case, the
Wireless HART Gateway and all Wireless HART devices must be configured with the same Join Key.
In the second case, which provides higher communication security level, (a) must be configured in
the Wireless HART Gateway a list with individual Join Keys, i.e., a key for each Wireless HART
device, and (b) you must configure each Wireless HART device with its individual Join Key. The Join
Key is a hexadecimal string of 16 bytes. There is no restriction to the hexadecimal value of each
byte. The table below shows examples of some join keys.
JOIN KEYS 16-BYTES HEXADECIMAL STRING
00000000000000000000000000000000 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
00000000000000000000000000000302 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x02
00000000FFFFFFFF0000000000000000 0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
550000000000000000000000000000AA 0x55, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xAA
Wireless HART device
The Wireless HART field device is the device that connects to the process, being able to receive
and/or transmit data on the Wireless HART network. It is a Wireless HART router (repeater) by
nature, i.e., it is able to retransmit messages to/from other devices on the Wireless HART network.
Wireless HART Adapter
It is a bridge-type device, because it is able to provide data of HART + 4 to 20mA field device,
legacy, to the host via Wireless HART. The adapter uses HART FSK standard communication,
wired, to access data from HART field devices. And the adapter also uses the Wireless HART
communication to provide data of the field device to the host. The adapter thus enables a HART
field device to work on Wireless HART network.
We recommend a visit to the HART Communication Foundation website for additional information
about the
Wireless
HART protocol such as
Wireless
HART project planning, positioning of devices,
commissioning and verification tools, and practices.
Planning an Wireless HART network
The planning of a
Wireless
HART network is a task that is very similar to the activities that currently
we perform with conventional wired devices. Furthermore, due to the simplicity of a mesh
Wireless HART network, is exempt, in general, detailed field surveys, which are usually needed
when we plan networks based on other wireless technologies.
Basically, a Wireless HART network involves planning, design, installation and commissioning
phases.
Planning
This phase requires the execution of the steps below:
Scope definition
Clearly define the scope of the network. Answer the question: why do we need the wireless
network? To monitor process variables or to implement a non-critical control? The answer to this
question will facilitate the understanding between the team members responsible for the network