5/15/2010 12:49 PM | |
Joined: 10/7/2005 Last visit: 7/15/2024 Posts: 3009 Rating: (1053)
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Hello MemoGG no need to worry too much. Any DPV1 related Datarecord read or write (e.g SFC58/59 or SFB 52/53 usage) takes place on the Profibusas a so called acyclic transaction. Unlike cyclic data (which every DP Slave provides every Profibus cycle),the DP Master is only "allowed" to accomodateone additional acyclic transaction per Profibus cycle (irrespective of how many datarecords from how many devices you may try to request per PLC scan). The worst case effect you will/can as such create by reading out datarecords from each Simocode,would be the same as having one additional DP Slave on the bus with 244 Bytes of Inputs (orOutputs). What this also means is that reading out of datarecords from a number of DP Slaves will take time. Let's say you have the following - 100Simocodes on one Profibus Network - atypical Ttr (Profibus cycle time) of 20ms, - read of one Datarecord from every Simocode --> the best update time you could possibly expect for readingall 100 Datarecordsisnot even 2 seconds (200ms * 100) but instead 4 seconds (you will get the Datarecord back at the earliest in the next Profibus cycle). The other thing to be aware of is that there is a limit on how many SFC58/59 or SFB52/53 calls you can have active at any given time in the PLC and you can find these limits HERE. Multiplexing of the Datarecords requests is thus the way to go and while this adds a bit to the programming effort, it is a worthwhiele effort in my humble opinion. You will be rewarded witth a wealth of nice information (Datarecord 92, 94 and 95 are my must have Simocode ones)and the Plant owner, Maintenance personelland Operators will (shall) be forever grateful (assuming you make the read out values available on the SCADA system). I hope this helps |
Cheers |
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