NetAlert NetMeter User Manual page 21

CANH/L Diff. V (D)
Thresholds:
Diff D Voltage High Fault
Diff D Voltage High Warning
Diff D Voltage Low Warning
Diff D Voltage Low Fault
What is "Dominant"?
DeviceNet messages consist of 1's and 0's. The
dominant state of the bus (where the differential voltage
between CANH and CANL is around 2V) represents the
logical value 0 (opposite from what you might expect).
The bus can only be in the dominant state when a node
is actively transmitting.
NetMeter measures the difference between CANH and
CANL for dominant bits on the network, and if the
difference is not within acceptable limits, NetMeter
indicates a warning or a fault.
For CANH/L differential dominant voltage
levels we suggest:
!
Check for shorts and opens on the CANH and
CANL wires
!
Check for a missing, bad, or extra terminators
(should be two 120 ohm terminators from
CANH to CANL - one at each end of the
network and no more
! Disconnect nodes one at a time or temporarily
split the network to check for faulty transceivers
or cables.
!)
CANH/L Diff. V deals
with these two wires
(CANL & CANH)
8
3.00V
2.75V
1.45V
1.20V
21