Had a good break down today. I had random drive alarms on the scada page causing the clients plant to shut down. After following through the code i determined that the fault register reads from certain drives were not being received. Unfortunately it would only happen once every 10 to 25 minutes. The original programmer was writing FFFF to the respective fault destination registers in the plc and allowing up to 10 seconds for the receive read to update the register with 0000 which if it wasn't done would set one of the fault bits.
After following a calculated hunch I found a damaged cable close to where I thought the problem was and repaired it. Sweet, all working now.
Now for the indestructable part, this plant has all the modbus 485 done in cat5 obviously unshieled, running hard up against mains cabling (cable tied in the same loom) and unshielded VSD cables (yes, unshielded). Probably 600m all up with 15 slaves. I cant believe this network works. I read alot about how important shielding and grounding is of field bus networks, but this place throws all that out the window. Its hard to describe in words what I saw but its a miracle this place runs. And at 19.2 baud.
Its not good to know what you can get away with!
After following a calculated hunch I found a damaged cable close to where I thought the problem was and repaired it. Sweet, all working now.
Now for the indestructable part, this plant has all the modbus 485 done in cat5 obviously unshieled, running hard up against mains cabling (cable tied in the same loom) and unshielded VSD cables (yes, unshielded). Probably 600m all up with 15 slaves. I cant believe this network works. I read alot about how important shielding and grounding is of field bus networks, but this place throws all that out the window. Its hard to describe in words what I saw but its a miracle this place runs. And at 19.2 baud.
Its not good to know what you can get away with!
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