Soft­ware ver­si­on 2.36 for CAN­touch – mea­su­rement of Level Ratio

Logo CANtouch ScheinNew mea­su­rement Level Ratio

The new soft­ware ver­si­on from Sep­tem­ber 2019 comes with a new mea­su­red value for the CAN bus, the level ratio. This new mea­su­red value faci­li­ta­tes the detec­tion of short cir­cuits and tran­si­ti­on resis­tan­ces in a wire or bet­ween wires as well as of elec­tro­nic faults in CAN nodes. The dif­fi­cul­ty in detec­ting pro­blems with cer­tain abso­lu­te vol­ta­ge levels is that simi­lar con­stel­la­ti­ons can also ari­se due to Com­mon Mode. It was, the­re­fo­re, necessa­ry to find a way of reli­ab­ly dis­tin­guis­hing per­mis­si­ble com­mon-mode shifts from cases of a short cir­cuit or con­tact resis­tan­ce.

Until now, cer­tain errors could only be detec­ted indi­rec­t­ly, for examp­le, the short-cir­cuit from CAN_​L to ground. The pro­blem was only visi­ble in the phy­si­cal oscil­lo­scope image. The Auto­ma­tic Quick Test was able to eva­lua­te the bus com­ple­te­ly well even though a line was faul­ty. Due to the addi­tio­nal mea­su­red value level ratio, the CAN­touch now reli­ab­ly detec­ts such errors.

CAN Bus Level Ratio CAN_H/CAN_LThe level ratio descri­bes the per­cen­ta­ge sha­res of CAN_​H and CAN_​L in the dif­fe­rence signal for the domi­nant bus sta­te. 100% are dis­tri­bu­t­ed over the two lines CAN_​L and CAN_​H, wher­e­by a dis­tri­bu­ti­on of 50% to 50% is opti­mal. Devia­ti­ons from the ide­al occur, for examp­le, when tran­si­ti­on resis­tan­ces or short cir­cuits occur from a line to the sup­ply vol­ta­ge or ground. The trans­cei­vers with 3.3V power sup­ply instal­led in some nodes have a nega­ti­ve influ­ence on the level ratio, wher­e­by the pre­set eva­lua­ti­on thres­holds were selec­ted in such a way that this slight shift of round about 5% does not signal an error.

As is usu­al with the CAN­touch, the eva­lua­ti­on limits in the cantouch.property.rating.xml file can also be set pro­ject-rela­ted for this mea­su­rement. The default set­ting cau­ses the out­put of a warning if the sha­re of one of the lines falls below 30%. A value below 20% is con­si­de­red an error.

Sep­tem­ber 2019