ControlNet NetChecker
9
Rockwell Automation Publication 1788-UM001B-EN-P - August 2012
Note that when the Node On Line status indicator is red, it generally does not mean that
the node itself is bad, but rather that the signal received by the NetChecker from this
node is affected by a problem on the network. An impedance mismatch may cause some
nodes to be received as good (Node On Line status indicator green) while others are
received as bad (Node On Line status indicator red). Testing at another point on the
network will show that nodes that were received as bad are now received as good or vice
versa. If a Node really is bad it will appear bad everywhere on the network. The
NetChecker can only rely on the signal it receives at one point on the network. That is
why a network should always be checked at several points.
Buzzer
The Buzzer sounds any time a fault is detected.
Node Finder and Oscilloscope Output
The address (MAC ID) of the message originator is the only information from a message that
can be decoded by the NetChecker. This address is compared to the address entered on the two
thumbwheels (the possible node addresses range from 01 to 99). Depending on the setting of
SW3, the comparator either activates the Node On Line status indicator (Diagnostic mode) or
enables the display of the level of signal received from the node (Bargraph mode).
The Node Finder also provides a synchronization signal for viewing the messages from a given
node with a digital storage oscilloscope (DSO). This signal (trigger) is provided on the 3-pin
connector on the left side of the NetChecker. The connector pin labeled “Signal” delivers the
signal from the network via an input transformer with a 1:4 isolation stage. The NetChecker
ground is provided on the center pin.
The Trigger signal rises at the end of the transmission
of the originator address (MAC ID) if the
address matches the number on the thumbwheels (set the oscilloscope trigger to rising edge). We
recommend fastening small pieces of solid copper wire (1 inch long 18-22AWG) to the terminal
block for attachment of the oscilloscope’s probes (preferably high impedance 10:1 probes). Also
remember that the peak-to-peak voltage on the Signal pin is one fourth the peak-to-peak voltage
on the network.
Bargraph Mode
When slide switch SW3 is in its rightmost position, the Bargraph mode is enabled and status
indicators 1 to 7 function as a maximum/minimum signal level indicator. This indicator displays
the level of the signal from the node selected by the Node Finder. When the Node Finder is set
to 00, it provides a global view of the signal level (maximum and minimum) of all the messages
seen on the network.
In Bargraph mode, the Poor Signal Quality and Illegal Framing detections are performed with
the threshold defaulted to M (medium). If Poor Signal Quality or Illegal Framing are detected,
they are signalled only by the buzzer. The Slow Edges detection is not performed in Bargraph
mode.
