bUs error on Yaskawa P1000 Ethernet VFD to Controllogix

3 posts in this topic

Good Day,

I am seeing intermittent bUs (communication bus) errors on 3 VFD's simultaneously.  These are Yaskawa P1000's with CM092 Industrial Ethernet Cards.

There are Stratix 5700 switches between the drives and the Controllogix 1756-L75 CPU.  Happens every day to every week -- intermittent.

Reading parameter F6-98, it indicates a 'connection time out'.  I don't understand why I would receive this fault.  IGMP snooping and querier are enabled on all switches, if that matters.

I do not have unicast checked but Yaskawa said that didn't matter.  Packet time is 100 milliseconds.  I welcome any input on what might cause this.  One Yaskawa tech said I should set speed to 100 Mbps (now set at 10 Mbps).

Any help appreciated.

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Hi fseipel22

Firstly welcome to the forum.

What about alarms on the ControlLogix? Are you actively monitoring the status of these drives via the entrystatus tag?

If not, it might be worth enabling this so you can track and cross reference your alarms...




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In general, modern Ethernet systems should be allowed to use "Auto-Negotiate" to set speed and duplex.    If you have configured only the VFD to use 10 Mb/s, then the managed switch may still be set to "Auto-Negotiate".

"Auto-Negotiate" is not "auto-detect".    There is a low level protocol for testing the link at 10 or 100 mb/s and at full or half duplex.    In general that's done each time the link is broken (unplugged) and re-connected.

But some switches when they have an Auto-Negotiate failure (because the connected device is hard-set to 10 MB/s) will periodically attempt to re-negotiate so they can establish 100 Mb/Full Duplex.

This causes drops of connections on that port, when the switch decides to do a new link negotiation cycle.

So unless you have a very good reason to set the VFD to 10 Mb/s on the Ethernet port, I strongly suggest setting both the switch and the VFD to "Auto-Negotiate".

A sophisticated switch like the Stratix should have some logs for you to examine, but I'm not enough of a Cisco IOS expert to tell you how.

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