Rockwell Automation 1788-CNCHKR ControlNet NetChecker User Manual - Manual (Page 8)

8 ControlNet NetChecker
Rockwell Automation Publication 1788-UM001B-EN-P - August 2012
Status Indicator Functions
When slide switch SW3 is in the Diagnostic (left) area of the front panel, the status indicators
have the following functions:
• Pass/Fail status indicator—Indicates the overall quality of the signal on the coaxial
cable. Green when the input signal is clean, this status indicator will turn progressively
red if one or more of the criteria of quality are violated.
• Poor Signal Quality status indicator —Blinks red when the message signal is distorted
and/or when the between-messages gap is polluted by noise so that the NetChecker is
uncertain if the signal received is a valid message or noise. Distortion and noise are
generally the result of reflections of signal on the cable caused by impedance mismatches.
The Poor Signal Quality fault detection is dependent on the threshold settings L, M, and
H on SW3.
Note that there area number of violations to the Manchester encoding in the ControlNet
frame (in Start and End Delimiters). The NetChecker can detect if there are fewer or
more violations than expected. In the case of very large distortion of the signal the
NetChecker may interpret that there are unexpected violations although the message
was generated correctly by the originator node.
• Illegal Framing status indicator—Blinks red when erratic message detection occurs.
The NetChecker verifies the duration of messages and generates a fault if any message is
shorter than 7 bytes (NULL message length). In addition, the time gap between
messages must not be less than 6 bytes. These errors are generally caused by high noise
level or signal reflection at the end of the messages or during the time gap between
messages. These faults are the result of large impedance mismatches on the network.
This fault detection is dependent on the threshold settings L, M, and H on SW3.
• Slow Edges status indicator—Blinks red when the NetChecker has identified a weak
signal with poor rise/fall times. This may result from high signal attenuation caused by
bad coaxial cable, excessive cable length, or an overloaded network. This fault detection
is not dependent on the threshold settings on SW3.
• Node On Line status indicator —Turns green if a node having the address entered in
the Node Finder is detected on the network and the signal received from it is good. The
status indicator will turn red or appear yellow (rapidly flashing red and green) if the
messages received from this node exhibit one or more of the faults signaled by the fault
status indicators.