The Basics
The Network
SKF Wireless Machine Condition Sensor
9
Service Manual
Term
Definition
P2 profile
2048 slot superframe, 20.48 sec cycle; better battery life, poor
user interface response and
slower join process.
P2 is eight times slower than P1; the network assigns the same
number of slots but eight times farther apart.
Power profile
High or low power device. See the section
Routing device
A device that participates in the mesh network, meaning it “helps
its neighbor” when the neighbor does not have direct access.
Short tag
Pre-HART7 8-character logical name for the HART device.
Slot
A fixed time interval that may be used for communication between
neighbors.
Security manager
Responsible for the joining process of the device and ass
igning the
session key to encrypt and decrypt packets.
Superframe
A collection of slots repeating at a constant rate. Each slot may
have several links associated with it.
KNOWN ISSUE:
P2 profile is not working in the P+F gateway. However, it may work in
gateways from other manufacturers.
The WirelessHART Network Joining Process
This is a simplified sequence of how the sensors join the network.
•
The active gateway sends network advertisement signals. These are messages
sent by the network manager to announce the network’s existence. The network
manager and security manager are contained in the gateway.
•
The sensors respond with a Join Request, which consists of the Network ID and
Join Key. The security manager authenticates the Network ID and Join Key and
then allows the sensor to join the network
.
•
The security manager sends session keys to the sensors and routing and
scheduling information.
•
The sensors begin normal operation, which is publishing data (the four main
variables and device status, as described below).
Network Layers
Physical Layer
•
IEEE 802.15.4
•
ISM band 2.40 – 2.48 GHz
•
16 x 5 MHz non-overlapping channels in 80 MHz bandwidth