Rockwell Automation 1788-CNCHKR ControlNet NetChecker User Manual - Manual (Page 14)

14 ControlNet NetChecker
Rockwell Automation Publication 1788-UM001B-EN-P - August 2012
Faults and Their Origins
The NetChecker checks for Poor Signal Quality, Illegal Framing, and Slow Edges. If a fault is
detected when checking in the Diagnostic mode, the buzzer will sound and one or more of the
three fault status indicators will blink red.
The detection of Poor Signal Quality and Illegal Framing depends on the threshold setting on
SW3. Generally, faults that are detected at the L (Low) threshold level will disappear or be seen
less frequently as the threshold is increased. However, in some cases where the received signal has
a low level (less than 2 on the bargraph scale), faults may appear or their recurrence may increase
as the threshold is raised.
Use the table below as a guideline when evaluating your network.
The third type of fault detection, Slow Edges, checks for a low signal with poor rising and falling
edges caused by an abnormal attenuation of the signal. This fault detection is not dependent on
the threshold setting of SW3.
When analyzing a network, the NetChecker indication may differ from one point of test to
another. A network may be acceptable if the NetChecker reports faults with a low (or even
medium) threshold setting at some points, but a network that exhibits faults everywhere should
be inspected.
Try to evaluate residual problems using the Node Finder and an oscilloscope to ensure that the
signals meet the ControlNet requirements. Examine the nodes that are reported faulted (the
Node On Line status indicator appears red or yellow) and analyze the messages: the faults may
come from signal distortion, signal weakness, poor edges, noise, or signal reflections.
Threshold (SW3)
L M H Network quality at the point of test
No fault No fault No fault Very clean
Fault No fault No fault Clean, acceptable
Fault Fault No fault May be acceptable after cabling inspection
Fault Fault Fault Network needs inspection
IMPORTANT If faults are reported for all three threshold levels, then it is highly probable that there is a
severe problem on the network.
TIP Remember that the purpose of the NetChecker is to alert for possible problems with network
cabling and that its sensitivity is greater than required by the ControlNet specification.