6/28/2010 3:50 AM | |
Joined: 9/27/2006 Last visit: 9/20/2024 Posts: 12282 Rating: (2684) |
Hello lalit; Modbus was never designed for high-speed data exchanges, and deterministic cycle times originally; it tends to emphasize repeatabililty over speed. With Modbus, the overall cycle time will depend on many factors: -communication parameters. Siprotec relays seem to be able to reach comm speeds of 57600 bits/s under certain versions; what is the max speed of the master you are using (lowest speed wins); see this document from siprotec.de http://siemens.siprotec.de/download_neu/devices/1_General/Doku_Protokolle/Englisch/Modbus/Modbus_with_SM_3-1_since_3-n/COM_MODBUS_PROFILE_US.PDF -Modbus master parameters: generally the master can be configured with certain elements that can speed up or slow down the Modbus exchanges: number of retries, maximum cycle time, amount of diagnostic data... The lowest protection offers the quickest cycle. -the number of slaves and the amount of data required from each one is very important, and cycle times increase with both of these. You can try to optimize by testing a few slaves at a time with the highest speed possible, the smallest footprint of the Master's controls and the minimum required data, and see if you can reach your objectives. Hope this helps, Daniel Chartier |
Last edited by: dchartier at: 6/30/2010 4:27 AMLast edited by: dchartier at: 6/28/2010 3:55 AM |
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This contribution was helpful to2 thankful Users |
6/28/2010 5:07 AM | |
Joined: 12/20/2008 Last visit: 8/12/2024 Posts: 556 Rating: (236) |
Hi Dchartier, Thanks for clarifying, however, I am going to check if I can change the baud rate in Sprotek relays. However though I am not sure but just for clarification will the response time get change if I would use Modbus over TCP/IP instead of Serial communication. I think as long as the parameters(baud rate) on both sides(master and Slave) are same then it would not matter weather it is Serial or Modbus over TCP/IP. However one of our vendor suggested to go for it. Please clarify. Thanks, |
6/29/2010 3:40 AM | |
Joined: 12/20/2008 Last visit: 8/12/2024 Posts: 556 Rating: (236) |
Hello Experts, I am still waitingthe response to get this resolved. Please provide your valuable inputs. Thanks,
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6/29/2010 7:57 PM | |
Joined: 9/27/2006 Last visit: 9/20/2024 Posts: 12282 Rating: (2684) |
Hello lucky; I think ypou should start your search on sites that specialize in Modbus issues, such as: http://www.modbus.org/faq.php. You would find statements like these: What sort of performance can I expect from a Modbus TCP/IP system? The performance depends on the network and the hardware. If you are running Modbus TCP/IP over the Internet, you won't get better than typical Internet response times. However, when communicating for debug and maintenance purposes, this may be perfectly adequate and save you from having to catch a plane or go to site on a Sunday morning! For a high-performance intranet with high-speed Ethernet switches guaranteeing performance, the situation is completely different. In theory Modbus TCP/IP carries data at up to 250/(250+70+70) or about 60 percent efficiency when transferring registers in bulk. Since 10BaseT Ethernet carries about 1.25 Mbps raw, the theoretical throughput is 1.25M/2 * 60% = 360000 registers per second and the 100BaseT speed is 10 times greater. This assumes that you are using devices that can service Ethernet as fast as the available bandwidth. Practical tests carried out by Schneider Electric using a MOMENTUM™ Ethernet PLC with Ethernet I/O demonstrated that up to 4000 I/O bases could be scanned per second, each I/O base having up to 16 12-bit analog I/O or 32 discrete I/O. Four bases could be updated in one millisecond. While this is below the theoretical limit calculated above, remember that the tested device was running with only a 80186 CPU running at 50 MHz with an effective computing power of 3 MIPS (compared to the 700 MIPS of a 500 MHz Pentium). Nevertheless, these results are faster than the proprietary I/O scan methods used to date. As low-end CPUs get less expensive, Momentum-type devices will chase the theoretical limit, although they'll never reach it because the limit will continue to be pushed further away with 1 Gigabit Ethernet, 10 Gigabit Ethernet, etc. Contrast this with other field-buses, which are inherently stuck at one speed. |
Last edited by: dchartier at: 6/29/2010 8:06 PMLast edited by: dchartier at: 6/29/2010 7:58 PM |
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1/15/2015 11:02 AM | |
Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4767 Rating: (123) |
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