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Wave form in Profibus DP - help

9/6/2012 5:40 PM	Rate (0)
Pedro Ascencio Posts: 56 Rating: (2)	Dear Experts I need your advice please. I have a Profibus DP network, and I would like which is the maximun voltagedrop allowedbetween the Master and its Slave. Currently I have 6.08 Vin the Master and 5.24 V in a Slave, and occurs some random errors in the communication links. Many thanks in advance
Pedro Ascencio Posts: 56 Rating: (2)	Last edited by: Pedro Ascencio at: 9/6/2012 10:33 PM
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9/6/2012 7:47 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/23/2025 Posts: 12344 Rating: (2707)	Hello Pedro; Unlike other buses that are loop-powered (Profibus-PA, FF...) Profibus-DP requires that all nodes be locally powered at 24 VDC, so the electronics (especially the line drivers)will all have the required voltage and power. So if your bus is "properly" installed, well-grounded. with Class-A cable and connectors and correct termination procedures, if your segment length is appropriate for the communication speed selected, then voltage drop should not be a problem. By the way, where did you take these voltage measurements (between which pins?), and what instrument (DC voltmeter?). If you feel you need a quickrefresher course on Profibus network installation, you could look at this web-based training prepared by Profibus International: http://www.profibus.com/fileadmin/media/wbt/WBT_Assembly_V10_Dec06/index.html Or you could download some of the pdf available from the same site overviewing Assembly and Commissioning of Profibus networks: http://www.profibus.com/nc/downloads/downloads/profibus-installation-guideline/display/ Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 9/6/2012 7:48 PM
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9/6/2012 10:02 PM	Rate (0)
Pedro Ascencio Posts: 56 Rating: (2)	Dear Daniel Many thanks for your help. This voltage were neasured by profiTrace between A-B lines. I followed your links and finally I end up analysing the communicationwaveform. Perhaps, I have some reflections in our profibus cable which could be the blame for loosing the communication (I attach the ware form recorded). I will check earths connection as well. Please, any oppinion about the communication pattern is very welcoming. Kind regards Attachment comm_pattern.jpg (145 Downloads)
Pedro Ascencio Posts: 56 Rating: (2)
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9/7/2012 8:18 PM	Rate (0)
Pedro Ascencio Posts: 56 Rating: (2)	Dear Daniel Sadly, or luckily, I foundtwo earth connection missing and connector without shield. Iexpect that it is the reason forour random communication fault. Many thanks in advance
Pedro Ascencio Posts: 56 Rating: (2)
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9/7/2012 8:42 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/23/2025 Posts: 12344 Rating: (2707)	Hello Pedro; Good for you, and I do hope this will result in better communications in your project. Whenever you have such a problem in you comms systems, I cannot stress enough that you must go back to the very basics, and never assume that the physical layer has been perfectly installed. It does not take much for such a small disturbance to unbalance the whole network. Regards, Daniel Chartier

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