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Urgent help required. Change of Trigger cycles in SCADA from "Upon change" to "Cyclic - per second", will there be impact on system performance/response time?

Created by: ericlim001 at: 5/6/2009 4:11 AM (7 Replies)

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5/6/2009 4:11 AM	Rate (0)
ericlim001 Posts: 6 Rating: (0)	Dear Experts, I need your advice urgently. I am an end user who is not familar with the Simatic WinCC. Currently, we have a dual redundant S7-400 PLC controlling a process plant with around 8000+ IO tags, the SCADA retrieves data from each tag via trigger cycle "Upon change". There is a requirement to change the trigger cycles for all tags in SCADA from "Upon Change" to "Cyclic - per second". I need your advice on whether there will be a major impact on system performance or response time or none at all? Please help asthey are pressing to implement the changes. Currently per tag we record about 400 values daily. By changing to Cyclic- per second, the number of values recorded will increase from 400 to approx 86400. Is this correct? Please advise. Regards Eric
ericlim001 Posts: 6 Rating: (0)
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5/6/2009 5:51 AM	Rate (0)
ericlim001 Posts: 6 Rating: (0)	Dear Experts, I wish to clarify on the issue. Currently, out of the 8000+ tags, only 300 are analog inputs/process variables that require change of trigger cycle in SCADA from "upon change" to "cyclic - every second". Currently, average 400 values are recorded per tag over a period of 24 hours. We calculated that by changing to cyclic every second, a total of 86400 values shall be recorded per 24 hours. Is this correct? Hence, the question whether the change of trigger cycle of these 300 process variables will impact the system performance/response time? And when this segment of values are archived to a data server, how big a harddisk is required to store the increased number of values? Please advise. Thanks for your help. Regards Eric
ericlim001 Posts: 6 Rating: (0)
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5/7/2009 12:35 AM	Rate (0)
Phantom75 Posts: 2661 Rating: (279)	May be I am missing something here but I do not fully undestand the question... What do you mean by recording the values? Are you talking about archiving (tag logging)? Then what has that got to do with trigger cycles? Regards
Phantom75 Posts: 2661 Rating: (279)	Last edited by: Phantom75 at: 5/7/2009 3:49 AM
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5/7/2009 2:47 AM	Rate (0)
ericlim001 Posts: 6 Rating: (0)	Hi Phantom75, Pardon me as I am not versed in this field. Please allow me to clarify. We have 300 process variables/tags sending process values from field, e.g. flow rate 200m3/hr, pressure 3.0bar, etc. Currently, when the values do not change, the data is not logged. I was told this setting of "upon change" is part of the trigger cycle for WinCC to log the values. Perhaps I got the name wrong and it is not trigger cycle. I was told that by changing the setting from "upon change" to "cyclic - every second", the total number of process values recorded will increase by 24hours60mins60seconds = 86400 values per tag. Is this correct? If so, will the data logging of this 86400 values per tag slow down the system performance/response? I will appreciate your reply and advise. Thanks! Regards eric
ericlim001 Posts: 6 Rating: (0)
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5/7/2009 4:17 AM	Rate (0)
Phantom75 Posts: 2661 Rating: (279)	Hi Eric, So we are talking about process value archiving. I am not sure how you have implemented the so-called upon change archiving. How fast do the values change? For how long do you store the values? Generally speaking (in my opinion) logging 300 values at 1 sec should not have any appreciable impact on system performance (see attachment in following thread regarding performance data, chapter 5 Response time calculations ). I have attached pages from the manual that describe process value archiving for your reference. Regards Attachment ArchivingProcessValues_ WinCCbasis_V6_e.pdf (224 Downloads)
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5/7/2009 7:59 AM	Rate (0)
ericlim001 Posts: 6 Rating: (0)	Thanks for the manual! We are using a similar setup as Scenario 3 on pg 186. May I clarify on the following and ask Qns 1 and 2? Thanks "I am not sure how you have implemented the so-called upon change archiving. How fast do the values change?" -- Currently, lets say the process value is a flow rate at 120m3/hr. If there is no change over 5mins for this value, it is only logged once as 120m3/hr. If a change occurs after 3mins or 10mins, then the data will be logged at that time. The concern is that all different flows will have different time stamps that will cause the data log to be useless, that is why they are requesting to change to cyclic - every second such that all values will be recorded at same time. "How fast do the values change?" It is dependent on the stage of the process. During the startup and rampdown stage, the values change rapidly. However, after stablising, the values are fairly constant. 1)MayI ask ifyou mean thatlogging 300 values at 1 sec from the Data Manager(DM) to the Archive system should not have any appreciable impact on system performance? 2) May I ask regarding the link between WinCC and automation system whichis provided by process tags? I was told that in the acquisition cycle, process values are updated to process tags under the setting "Upon Change". When the setting is changed to "Cyclic- per second", will there be an impact on system load? Is it suggested to use message frame tags instead? regards Eric
ericlim001 Posts: 6 Rating: (0)
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5/8/2009 1:17 AM	Rate (0)
Phantom75 Posts: 2661 Rating: (279)	ericlim001 . . . ifyou mean thatlogging 300 values at 1 sec from the Data Manager(DM) to the Archive system should not have any appreciable impact on system performance? . . . For "normal" cyclical archiving, 300 values at 1 second is well within the performance limitations. ericlim001 . . . regarding the link between WinCC and automation system whichis provided by process tags? I was told that in the acquisition cycle, process values are updated to . . . Currently you are using scripts. In these scripts if you change the triggers from upon change to 1 sec cyclic, there definitely will be performance degradation. If you want to switch to 1 sec cyclic archiving, you should completely abandon the scripts (IMO)and setup the traditional cyclic archiving. This is easy to setup and probably can coexist with the old scheme... Regards
Phantom75 Posts: 2661 Rating: (279)
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5/8/2009 3:29 AM	Rate (0)
ericlim001 Posts: 6 Rating: (0)	Dear Phantom75, Thanks for your detailed advice! We will try to implement and revert with results.
ericlim001 Posts: 6 Rating: (0)
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