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Old November 14th, 2017, 12:26 PM   #1
dwoodlock
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random profibus drops

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.
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Old November 14th, 2017, 12:56 PM   #2
sigmadelta
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Termination should be ON at Servo3 and ET200/3. I would just unilaterally replace the Profibus connector at Servo3.
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Old November 14th, 2017, 01:37 PM   #3
mk42
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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).
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Old November 14th, 2017, 01:40 PM   #4
sigmadelta
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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.
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Old November 14th, 2017, 02:59 PM   #5
dwoodlock
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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.
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Old November 15th, 2017, 01:19 AM   #6
ojz0r
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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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