random profibus drops

dwoodlock

Lifetime Supporting Member
Join Date
Nov 2012
Location
Cincy/nKY
Posts
548
Wondering if anyone has run across an issue like this before.

Machine that's been running for probably 15+ years.

Profibus network physically arranged like so:
servo3-servo2-servo1-hmi-s7300-et200/1-festo1-et200/2-festo2-et200/3

keep getting random bus faults. We eventually figured out that if you turned on the terminator at servo 3 that it would cause a fault. Yesterday the fault came back and I went to the et module at the other end of the network and turned the terminator to the off position, what do you know the fault again went away.

I'm no profibus network guru.

Thanks in advance.
 
Termination should be on at both ends of the line. However, you also need to check whether you are using the A and B sides of the connector correctly.

If wrong, turning on the termination will prevent access from one of the sides (can't recall which).
 
The termination switch breaks the "outbound" side of the connector from the device.

At least on Siemens Profibus connectors, the "inbound" Profibus connection point is marked with an arrow towards the connector, and the "outbound" points in the opposite direction.
 
Yeah I checked to make sure the cables were entering and exiting on the right side on all connectors, this was my first question when my techs told me what they did to fix the fault.
 
I've ran into problems like this with profibus.

Many times it turns out that there is a bad connection in one of the terminations.

In one case it turned out to be a cable that went bad due to the cable moving alot when the machine was running. This fault was found using a profibus analyzer.
 

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