CAN-wiring
The sequence of the wiring test raises questions from time to time. We would like to explain why the process is as it is.
There are also a few tips.
For the measurement, the CAN bus tester 2 must be operated at 24V. The process in CANtouch is the same.
If your bus wiring has no lines for the voltage and/or no shield,
You can deselect the measurement of these lines in the settings.
To do this, click on the gear icon when CANtouch and select the non-existent lines.
In CAN bus tester 2, this setting is queried at the start of the measurement.
The sequence of measurement is as follows:
Preparations for step 1:
the system must be switched off (the bus to be measured must be voltage-free)
- Participants must be disconnected from the bus (input capacities could lead to errors)
- the terminations must be removed (they will be measured later)
- Attach testers at the beginning of the system
Measurement 1: Short-circuit
The resistances of the lines are now measured. They should be infinite, because no ladder must be connected to another.
There will be an error if you e.g. B. did not subtract any of the terminating resistors.
Short circuits or contact resistors between the conductors occur occasionally in poorly mounted plugs.
Preparations for step 2:
- a short-circuit plug is to be plugged on at the end of the bus - In the short-circuit plug, all pins are connected to each other.
Step 2: Line break test
At the end of the bus, the short-circuit plug connects all cables of the cable. The loop resistance and length of the cables are determined.
Measured values could deviate upwards, then interruptions and contact resistors.
If you have not deducted participants, the determined length may differ considerably.
Measuring very short lines is difficult. For longer cables, the determined values are more accurate.
Preparations for step 3:
- Remove short-circuit plugs
- Turn on scheduling at the end of bus
Step 3: Termination at the end
The terminating resistor at the end of the bus is now determined by calculating the previously measured loop resistors.
Preparations for step 4:
- Turn on scheduling at the beginning
Step 4: Termination at the beginning
In the last step, the terminating resistor at the beginning of the installation is determined by offsetting the terminating resistor at the end and the loop resistors.
- You may be able to leave participants on the bus. The bus length measurement may be influenced by this. This can display errors, e.g. if you also measure the power supply lines, the power supply is secondary low-resistance and connected.
- It should be remembered that you may already eliminate the error if you move many connectors. If you suspect wobble contacts, then it may make sense to measure with connected participants first.
- To start a measurement with step 1 without making the described preparations, a resistor between CAN_H and CAN_L of approx. Determine 60 ohm. Of course, this is considered an error, because in step 1 we expect very high resistances. However, in order to quickly determine whether both terminating resistors are OK, this may suffice even if the measuring device evaluates it as a fault. This is more difficult to assess with a long bus cable, since the loop resistors are added. Here you can only access comparative values from previous measurements.
- CAN bus tester 2 could be corrupted if you ignore the warnings of the software and start the measurement process with applied voltage. The CANtouch refuses measurement as long as voltage is present on the supply lines.