SKF Wireless Machine Condition Sensor
61
Service Manual
7
Network Planning and Diagnostics
In this chapter, we discuss general rules to follow when planning a new network or
extending an existing one. Important points about the devices, network capabilities and
communication stability are considered. The network diagnostic report is examined and
tips for troubleshooting common network problems are provided.
Network Planning
First, determine the location of the gateway. Ideally, it will be in the center of the
network to maximize the number of single hop connections. Elevation helps the
connectivity. It is best to mount the gateway with no obstruction around the antenna,
for example on a pole; otherwise, at least 15 cm (6 in.) away from the mounting wall.
Next, determine the number of 1-hop sensors, 2-hop sensors, etc. You can use a scale
map to place sensors (note: radio devices are also called motes) at all the required
sensing points for the network. If possible, the access points should be located near the
middle of the distribution of sensors to reduce latency and power usage.
On the map,
mark the gateway and access point location(s). Draw a circle with a 50 m (164 ft.)
radius around the access point. Not all sensors within this circle will be able to
communicate directly with the access point, but some sensors outside the circle will, so
it will generally balance out. The number of sensors inside this circle approximates the
number of 1-hop sensors in the deployment.
Next, draw a 100 m (328 ft.) radius circle centered at the access point. The number of
sensors in the ring between 50 and 100 m approximates the number of 2-hop sensors.
Repeat this process with circles of increasing radius size until all sensors have been
encircled and note how many sensors are in each hop. Three hops is the maximum
recommended distance for any mesh network.
Important Considerations
•
WirelessHART documentation suggests at least 25% of the devices should have
direct connection with the access point (or gateway). The more devices in direct
connection with the access point the better; it improves stability and reduces
latency.
•
If possible, a sensor should have a maximum of three hops in practice or the
network performance may slow considerably. Use multiple gateways if more than
three hops are required.
•
Each radio (sensor) should be within the estimated range of at least three other
devices to provide alternative links in the mesh network.
•
Disable the routing capability for the devices located at the site’s perimeter to save
battery power and promote security. Do this on the gateway’s
Operations Mode
web page in the
Routing Device
column.