Com­mon Mode Measurement

To do com­mon mode mea­su­re­ments (expl­ana­ti­on here) with the CAN-Bus Tes­ter 2, you need a DSO, trig­ge­red by the CBT2’s trig­ger out­put. Start a con­ti­nuous mea­su­re­ment of the node you want to trig­ger to (the first mes­sa­ge in the oscillogram).
You will see pic­tures like this:

The CAN-Bus Tes­ter 2 can­not mea­su­re abso­lu­te values, that’s why it only see’s the dif­fe­ren­ti­al signal, which is dis­play­ed oran­ge in the oscil­lo­gram. The oscil­lo­scope shows the poten­ti­al dif­fe­ren­ces. Mes­sa­ges that only occur in big­ger inter­vals should be mea­su­red individually.

Easier is this mea­su­re­ment with the CAN­touch. It can mea­su­re abso­lu­te values against a refe­rence poten­ti­al, values the mea­su­red data and shows the case in the upper oscil­lo­gram on the same bus as dis­play­ed left.

It is clear that we have mes­sa­ges with poten­ti­als hig­her and lower to the mea­su­re­ment point. The com­mon mode vol­ta­ge is 3,00 V at all.

To do the same with the CBT2, one would need the tes­ter, a lap­top, the DSO and power for every item. All this must be con­nec­ted and the DSO must be pro­per­ly adjus­ted. With CAN­touch the sin­gle thing to do is to con­nect the bus – switch on and you are rea­dy to start.

We found a bet­ter name for this pro­blem recent­ly. Now we call it “ground shift”, that descri­bes this pro­blem much better.