CAN BUS did not return data sometimes

[iwanttofly014]

We got a very strange problem with CAN bus using NI PCI-CAN/XS2 card,the UUT(unit under test) did not return data sometimes,the strange thing is that it may return data in the next test loop.

Here is the detail:

We need to do some test for the UUT with NI PCI-CAN/xs2,the test is simple:put the UUT into temperature Chambers,and sent command to the UUT from PC,the UUT will return data to PC,We checked the that data to see if the UUT can still work in high temperature.there are 6 commands to test,after that,the UUT restarted,another same 6 commands will sent to the UUT again until test time is up. 6 command is one test loop.The cable between PC and UUT is about 10 meters.

The strange thing is that,event if we do the test in normal temperatrue,the UUT can not return data in some test loop,but It may return data in the next test loop.We did a whole night test in normal temperature,the UUT not return data sometimes,about 10 test loop in a whole night,the other test loops are working fine.no one touch the UUT or PC or anything else when testing the UUT.

We do some improvement to test system,when we got this problem,we added the 120 ohm terminal resistances to the both end of the CAN_H and CAN_L,replaced the cables with more twisted，shielded cable,and connected the CAN Reference Ground(Pin 2 in DB 9) the the UUT,connected the cable shield.but the UUT still can not return data sometimes.

 We monitor the CAN bus,the PC is working fine,it did sent the commands to the UUT when the UUT did not respone.we also change to another PC and CAN card,nothing change. We call the DLL in labVIEW to complete the CAN communication which we got from our client,I checked the VI,after it sent a command to the UUT,it used FOR loop the check the CAN BUS until it get the data or timeout,it return nothing when timeout(about 20 seconds),so the test fail.We try to increase the timeout to four minutes,still no work.

We asked our client about this problem,they said they never met this before,so,it seems the piont is not the UUT and program.

Question:

1,is anyone ever met something like this before?is there something we missed?

2,It seems the CAN BUS was disturbed by the other signals,what else can We do the prevent this happen? Any information is appreciate! Thanks for your time!