CAN wiring test

CAN wiring test

CAN wiring test

The sequence of wiring test raises questions from time to time. We want to explain here why the process is how it is?
There are also a few tips.

For the measurement, the CAN bus Tester 2 must be operated with 24V. The process in the CANtouch is the same.

If your bus wiring has no lines for the voltage and/or no umbrella,
You can opt out of measurement of these lines in the settings.
Click the gear icon on the CANtouch and select the non-existent lines.
At the CAN bus Tester 2, this setting is requested at the start of the measurement.

The sequence of measurement is as follows:

Preparations to step 1:
  1. the system is to be switched off (the bus to be measured must be voltage-free)
  2. The participants are to be disconnected from the bus (the input capacities could lead to errors)
  3. The terminations are to be removed (they will be measured later)
  4. Pocket testers at the beginning of the plant
Measurement 1: Short-closed test
The resistances of the lines are now measured. You should be infinite, because no ladder must be related to another.
There will be an error if you z. B. have not deducted one of the closing resistances.
Short circuits or contact resistances between the conductors occur gradually in poorly mounted connectors.

Preparations to step 2:
  1. A short circuit plug must be plugged up at the end of the bus - In the short circuit plug, all pins are connected to each other.

Step 2: Line break test
The short circuit plug connects all cables of the cable at the end of the bus. It determines the loop resistance and length of cables is determined.
Measured values could differ upwards, then searched for interruptions and contact resistances.
Have you not deducted, the determined length may differ significantly.
Measuring very short lines is difficult. For longer cables, the values determined are more accurate.

Preparations to step 3:
  1. Remove short circuit plug
  2. Turn on appointment at the end of the bus
Step 3: Termination at the end
Under Calculating the previously measured loop resistors, the closing resistance is now determined at the end of the bus.

Preparations to step 4:
  1. Turn on appointment at the beginning
Step 4: Termination at the beginning
In the last step, the closing resistance is determined at the beginning of the plant, accounting for the closing resistance at the end and loop resistors.

  1. You may have the participants on the bus. The bus length measurement may be influenced by this. This allows errors to be displayed, e.g. if you also measure the power supply lines, the power supply is secondary low-resistance and connected.
  2. It is to keep in mind that you might already eliminate the error if you move many connectors. If you suspect wobbly contacts, it may make sense to measure first with connected participants first.
  3. Starting a measurement with step 1 without making the described preparations will be resistor between CAN_H and CAN_L of approx. Determine 60 ohms. This is of course considered an error, because in step 1 we expect very high resistance. But to quickly determine if both terminating resistors are OK, it may be enough inny even if the measuring device assesses it as an error. More difficult to judge this for a long bus cable, as the loop resistances are added. Here you can only resort to comparative values from previous measurements.
  4. The CAN bus Tester 2 could be damaged if you ignore the software warnings and start the measurement process with applicable voltage. The CANtouch denies the measurement as long as voltage exists on the supply lines.