Measure canbus voltage

Robert Valk

Posted on 02.09.2016 08:59

Hello,


I'm using the DEWE 43 V analog inputs to measure the voltage of a canbus, I want to check if one of the components is making a short circuit, and see what this does to the traffic on the bus.

I tried several setups but I cant get what I want: to get some sort of scope showing the signals on the canbus (scope example) I understand there is lots of traffic on the canbus, but is there way to show the current signals without them flashing by making it impossible to identify?

And to get this signal visible, which ports should I use (now using analog 0: can high and 1: can low) and how to connect the wiring on the dsub 9 connector?


thank you in advance,

Robert

DEWESoft Support
Technical support
Posted on 06.09.2016 08:20

Hi,

I would suggest that you use the "Scope" visual control, which is meant to simulate the oscilloscope instrument. There is already a Scope view by default in DEWESoft, but you can also add it as a separate display, by selecting it from the design tab. From there, you have several options when selecting your viewing mode. If you want a more stationary picture, you can use the trigger mode, like I have in the attached example. The only thing that you have to take into account is the baud rate with which CAN messages are being transmitted/received. DEWE 43 has an upper limit of 200k samples per second, so you will be only able to see the correct signal for slow messages. A Sirius HS can go up to 1 million samples per second, but even that isn't enough to detect all of the pulses at the highest baud rates.

Since CAN uses a differential signal, it should be connected according to the wiring scheme that DEWESoft provides when entering channel setup (CAN high to pin 2, CAN low to pin 7 and the ground to pin 4). If you however want to view the waveform that can be seen in your picture, you can connect both the CAN high and low to separate channels, while also wiring a resistor according to the single ended connection scheme in DEWESoft.


Attached files:
Robert Valk

Posted on 09.09.2016 09:14

Hello,


I got it to work, got the can signal using the trigger as you suggested, thank you for the support,

for some reason the can high and low are both 2,5V when not sending a signal, do you know if this is normal?


kind regards,

Robert

DEWESoft Support
Technical support
Posted on 13.09.2016 07:45

Hi,

it's no problem. The 2,5V that you're seeing is the correct signal, since that's the voltage that's present in idle mode (when not data is being received or transmitted). You however won't be able to measure this signal with the new DEWE-43 and Sirius devices, because they are fully isolated.

Lula Nord

Posted on 08.03.2017 16:43

Hi...i am a new user here. As per my knowledge a simple voltmeter is all that is needed, to measure any CAN voltage it is easier to lift the complete strip connector, on the rear there are 2 metal strips running the length of the connector, one is CAN H and the other CAN L.If the car is all good and sleeping, that is with nothing running or active CAN L will have 11volts and CAN H 0.025 volts. If the car is active and one can make it active, just turn on the comand or open a door and you will see CAN L drop to 4.65 volt and CAN L go up to 0.65 volt. This voltage change when the CAN is active only last for a second and it should revert back to the dormant voltages.When checking the voltages you must wait long enough to be sure that something is not going to try and start up, and that the car really is sleeping, that is with 11volt and 0.025 volts respectively. If these voltages are correct, then no fault.

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