GE fanuc genius bus communcation problem

Dear all,

I'm facing a strange problem in genius bus communication.my system configuration is 90-30 hot redundant (software redundant) CPU372 with two nos of BEM & two no of CMM module in each CPU rack. It has 11 nos of versamax remote IO rack connected with GBI module via BEM with CPU.

The system was running commissioned and running perfectly for 7 years. Problem started from last month that randomly some or all GBI module stop working. IO enable of GBI change to amber instead if green. Some time only 1 or 2 racks out of 11 and sometimes all the racks. After resetting the power of GBI it again comes back to normal.

I have checked this with both the CPU and it is happening with both the CPU.
As the BEM is redundant so I guess all the BEM are not faulty. Same goes with the cable also.
I also checked the earthing and its okay.
Now I'm clueless. I can't understand why randomly BEM module breaks communication with GBI.

Please help me.

Was any hardware changed around the time when the problems first started?

Are there any entries in the PLC's fault tables corresponding with when the GBIs drop off?

Make sure the setting of the third rotary switch (Baud rate) on each GBI is the same. You may sometimes get away with a mix of 153.6K and 153.6K Enhanced on the same network, but it will eventually cause problems.

A failing power supply on a GBI could cause it drop off.

When you check the grounding pay attention to which cable shields are connected to the Shield In and Shield Out connections on each GBI to prevent ground loops.

No hardware was not changed it is same as it is.
Yes there is fault table in PLC saying remote node not found something like that. I will post the screenshot later.
Baud rate is same 153.6K for all GBI.

Some times say rack 1 GBI goes out sometimes Rack 3 and sometimes all the 11 racks, its uncertain and random.

Could u please elaborate your last point on how to prevent ground loop?
Should I ground each shield in and shield out of GBI with electronics earth?

Shield Out of one GBI should be connected to Shield In of the next GBI in the chain. At one end of the network cable there will be no connection to Shield In. At the other end there will be no connection to Shield Out. Make sure your terminating resistors are in place at the physical ends of the Genius network cable. The resistance should match the characteristic impedance of the cable you have selected. Make sure the total length of the network cable doesn't exceed the maximum for the type of cable and for the baud rate.

shield in and shield out are connected properly but the end terminating resistor is not present in the last rack, it was installed in some other rack i will add the resistor between A1 & A2 and revert back to you.

kakagi said:

shield in and shield out are connected properly but the end terminating resistor is not present in the last rack, it was installed in some other rack i will add the resistor between A1 & A2 and revert back to you.

Click to expand...

There must be terminating resistors at each end of the network only, remove any in the middle. If the GBI is on one end there may be a jumper using its internal resistor. Reference the IPI for your GBI.

Also verify that the cable has not been damaged or cut and spliced improperly near the time this started.

You may want to search here for more Genius Bus information:
https://ge-ip.force.com/communities/CC_Knowledge?q=Genius%20Bus