CAN Troubleshooting Guide
7.2 Electrical Grounding
The CAN_GND of the CAN network should be connected to the functional earth potential (FE) at
only
one
point. This test will check if the CAN_GND is grounded in several places.
To test it, please
1.
2.
3.
Disconnect the CAN_GND from the earth
potential (FE).
Measure the DC resistance between
CAN_GND and earth potential (see figure
on the right).
Reconnect CAN_GND to earth potential.
Figure 10:
Simplified schematic diagram of
ground test measurement
The measured resistance should be higher than 1 MΩ. If it is lower, please search for additional
grounding of the CAN_GND wires.
7.3 Short Circuit in CAN Wiring
A CAN bus might possibly still be able to transmit data if there is a short circuit between CAN_GND
and CAN_L, but generally the error rate will increase strongly. Make sure that there is no short
circuit between CAN_GND and CAN_L!
7.4 CAN_H/CAN_L-Voltage
Each node contains a CAN transceiver that outputs differential signals. When the network
communication is idle the CAN_H and CAN_L voltages are approximately 2.5 V measured to
CAN_GND. Faulty transceivers can cause the idle voltages to vary and disrupt network
communication.
To test for faulty transceivers, please
1. Turn on all supplies.
2. Stop all network communication.
3. Measure the DC voltage between CAN_H and CAN_GND
(see figure at previous page).
4. Measure the DC voltage between CAN_L and CAN_GND
(see figure at previous page).
Normally the voltage should be between 2.0 V and 3.0 V.
Page 26 of 29
Hardware Manual • Doc. No.: C.2048.21 / Rev. 1.1
CAN-PCI/400
>1M
CAN_H
CAN_GND
CAN_L
functional earth
(FE)
2
3
