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| 4/26/2010 12:41 PM | |
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Posts: 11 Rating:
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Hi Umencho, just wanna to check with u, is the ">32nodes with repeater "profibus rules application for PA network as well? Cause we do have about 60 devices on PA network.and once a a while we will experience some PA device lost communication "fail to communication by means of the BUS". please advise. thanks Splitted from Maximum Number of Profibus nodes on CP443-5 without repeaters. |
Last edited by: O_Moderator at: 4/27/2010 7:59 AMnew subject after splitting |
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| 4/26/2010 3:14 PM | |
Joined: 9/27/2006 Last visit: 11/7/2024 Posts: 12293 Rating:
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Hello Sean; the rule you mention ("32-node limitation without repeater") applies to RS-485 technology, upon which Profibus-DP is based. However, Profibus-PA is an instrumentation bus, very similar to Fieldbus Foundation, and based upon a different standard, IEC 61158-2. It also follows the FISCO parameters, which limits current consumption of transmitters in Ex zones. For example, there are 2 types of PA couplers available from Siemens, one is non-EX, and provides either 400 mA or 1A of power over the bus, and the other (Ex)provides only 150 mA. Each PA transmitter installed on the instruments consumes an average of 11 mA. So using an Ex PA coupler will limit you to around 12 instruments (PA slaves), no matter the length of the network. Using a non-EX coupler providing 1A might seem like you could go up to 80 instruments, but we have never installed more than 30 on our largest networks to maintain stable signals. At 31,35 kB (Siemens PA coupler speeds) or45,45 kB (Pepperl & Schutz PA coupler speeds), the maximum length of any PA bus is 1900 m. For further information, you could go to Profibus.com, under Downloads, and look up the PA documents: http://www.profibus.com/nc/downloads/downloads/profibus-pa-technology-and-application-system-description/display/ |
| 4/27/2010 4:57 AM | |
Joined: 10/7/2005 Last visit: 11/7/2024 Posts: 3026 Rating:
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Hello SeanL you will be asking for trouble ifthese 60 PA devices are all on one physical PA segment (and without the rarely usedPA repeater, irrespective if the PA coupler has enough current reserve and voltage drop is also not an issue). 32 Devices perSegment does apply as a rule for PA just as it applies for DPas far as I'm concerned (and a SiemensPA couplerwill limit you31 PA devicesper Coupler anyhow,theP&F coupler/power module allows 32 from memory). The other main thing tolook out for with PA is the Spurline lenght versus number of PA devices on a Segement(ideally you have less than 24 devices per Segmentto allow for up to 30 meters of Spurline length per PA instrument,have a look at table 3.5 on page 40 of THIS Profibus PA installation manual for more on this). For your info, P&F have a really nice tool called Segment Checker which - as the name suggests - allows you to check PA Segementdesigns. Best of all its a free download from here:http://www.segmentchecker.com I hope this helps |
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