Profibus slave fault

Guys,

We have been having issues recently with a profibus slave 11 dropping off of the bus. The device has been changed and prior to these issues has been running for 3 years with no issues. We have taken a screen shot of the diagnostic message using profitrace following a fault.

Can anyone shed some light using the error message as to what the root cause of the fault may be.

Thanks.

The slave looks fine in the screenshot you posted. Can u post the messages and the scope images from the time you had the problem?
If you don't have them a scope image from the current situation will do. But connect the scope as far away as possible from slave 11 in the same segment.

Profitrace has a scope function.
Take samples of A-gnd, B-gnd and A-B.

Profitrace should also have a function to capture an error the moment it occurs. I havent got experience with that though.

Please provide all details about the cabling.

Just because slave 11 drops off the bus, it doesn't necessarily follow that Slave 11 is faulty. The most likely cause of your problem is a cabling fault. I haven't used Proftrace much but I seem to recall that you can log dropped packets/retries agains slaves; see if the network in general is suffering packet loss. On the physical side, check that the bus is continuous from end to end (including the screen) with a terminator at each end but nowhere else.

Each terminating resistor is 240 Ohms. With the machine switched off or all the nodes unplugged, measure the bus resistance from one end of the bus; It should measure 120 Ohms with both terminatig resistors in circuit. First switch off the terminating resistor at the end you are measuring from, it should measure 240 Ohms (the other resistor); Switch the terminator back on again. Repeat this exorcise from the other end of the bus segment.

Good luck,

Nick