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OP77B on ProfiBus network gives spikes at A and B wire. Anybody have an idea why?

11/1/2010 6:39 PM	Rate (0)
wideko Posts: 45 Rating: (0)	The problem we found is that the OP77B is 'destroying' the signals at the A andB wire of the ProfiBus. There is a kind of a hartbeat at the wires with a frequency of approx. 250 kHz. (see picture) The ProfiBus network is like: - 1,5 Mbps - Start with an OP77B (6AV6641-0CA01-0AX0) - S7-414-3DP - ET200s (2 pieces) - Repeater (1 or 2) - (DP-DP-Coupler) - The slaves in the field. The Profibus-cable from PLC to the OP is (lukily) swapped. That's how we found the problem. We 'switched on' the terminator of the connector at the PLC and the cable to the field was working and the OP was diconnected. When the OP was disconnected, the signal at the A and B wires are as clean as the books are teaching. The OP is powered from the same Powersupply as the PLC. The wires to the OP are 0,75 mm2 (guess) Does anyone have an idea where this dirty hartbeat is coming from? And, of course, how we can solve this problem? withe regards, Willie Attachment 01_Segm1_Stat90_DP02out_DPisEnd_x.JPG (145 Downloads)
wideko Posts: 45 Rating: (0)
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11/3/2010 1:30 PM	Rate (0)
Sandman Platinum Member Joined: 4/29/2010 Last visit: 1/20/2025 Posts: 1557 Rating: (161)	Hello, have you allready check if EMC can be cause in this case and if the grounding is fine. best regards.

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11/3/2010 5:44 PM	Rate (0)
wideko Posts: 45 Rating: (0)	Hello Sandman, I have had a reply on my question via LinkedIn, from Dennis van Booma of Procentec. He asked me to disconnect the OP from the bus and connect it with the ProfiTrace tool. In his message he writes that if the signal is still the same, the OP will have a problem. And guess what, the signal is still there. Even worse, you can see the signal is realy going to clamp. If this display is having a problem, then more displays will have this problem. I have seen the hartbeat at several networks. regards, Willie
wideko Posts: 45 Rating: (0)
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