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Lifetime Supporting Member
Hello all,
Customer of mine has an RS-485 Modbus network. A PLC reads and writes to about a dozen drives. He was complaining about communication errors on the network. I looked at the software and raised the com error time to 90(!) seconds but that doesn't solve the problem.
Returned with a scope to the customer site today and saw the following wave-form. The edges look very nice so I'm doubting that it's a termination issue. The cables do run all over the place and there's lots of power cables not too far away. Termination appears to be OK as does the shielding. The cable is spec'ed as an RS-485 cable.
I'll have to return in a few days to take a good long look at everything but I'd appreciate any ideas as to where the source is most probably coming from.
(And sorry that the picture is upside down...)
Thanks all!
Yosi
Customer of mine has an RS-485 Modbus network. A PLC reads and writes to about a dozen drives. He was complaining about communication errors on the network. I looked at the software and raised the com error time to 90(!) seconds but that doesn't solve the problem.
Returned with a scope to the customer site today and saw the following wave-form. The edges look very nice so I'm doubting that it's a termination issue. The cables do run all over the place and there's lots of power cables not too far away. Termination appears to be OK as does the shielding. The cable is spec'ed as an RS-485 cable.
I'll have to return in a few days to take a good long look at everything but I'd appreciate any ideas as to where the source is most probably coming from.
(And sorry that the picture is upside down...)
Thanks all!
Yosi