5/17/2019 7:15 AM | |
Posts: 1 Rating: (0) |
6ES7972-0DA00-0AA0 is a terminating resistor, since it is 'resistor' , it should have resistance value. Could you please tell the resistance value? ------------------------------------------------------------------------------------------ |
Last edited by: Jen_Moderator at: 05/17/2019 07:18:54New subject after splitting |
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6/4/2019 3:48 PM | |
Joined: 9/27/2006 Last visit: 9/22/2024 Posts: 12282 Rating: (2685) |
Hello Dan; With Profibus-DP, termination must be active at both ends of the bus segment, on each end node. And most Profibus manuals will simply show you the selection of the terminating resistors, without details, as you can see in the attached screenshots. The images are from these documents: https://www.profibus.com/download/profibus-installation-guidelines/ https://www.felser.ch/profibus-manual/der_busabschluss_fuer_rs485.html However some sites are more dedicated to Profibus developers (rather than simple users) and show some interest in the physics of the bus termination. This is one: Uncovering the physical layer of PROFIBUS-DP Hope this helps, Daniel Chartier |
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6/4/2019 7:46 PM | |
Joined: 3/28/2010 Last visit: 9/21/2024 Posts: 1056 Rating: (213) |
Daniel, thanks for the links. I had no idea Profibus accounts for ground potential differences (common mode) way beyond the generic RS-485 -7 to +12V limit: From the EDN article: "The TIE/EIA-485-A standard specifies that ground shifts between two devices on a network can be as large as –7 to +12 V. However, many PROFIBUS-DP installations can encounter voltages much greater than this, which can cause critical damage to a PROFIBUS-DP transceiver. PROFIBUS is often used in 24-V systems, where shorting a “standard”RS485device to 24 V can be fatal. The designer should require a receiver with an extended common mode range of –25 to +25 V. Replacing the usual PROFIBUS-DP transceiver with the ±60-V protectedLTC2877can eliminate field failures due to overvoltage faults without costly external protection" The lack of extended common mode voltage creates lots of problems with generic RS-485 used in devices implementing Modbus RTU. |
This contribution was helpful to1 thankful Users |
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