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WinCC and PLC s7 synch cycle

Created by: slaven at: 12/8/2008 1:41 PM (7 Replies)

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12/8/2008 1:41 PM	Rate (0)
slaven Posts: 11 Rating: (0)	Hello! I have a project WinCC 2007 flex ans S7-300. I'm making 10 meagurments on the PLC one time per 1s and insert 10 value in DB, after that I try to read values from wincc, but cycle time in wincc and cycle time in PLC doesn't compare, so from time to time I have wrong values - one value on two cycle but the true value Ive lost. The question is - how can I sychronize time between Wincc and PLC? Thanks beforehand.
slaven Posts: 11 Rating: (0)
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12/8/2008 8:24 PM	Rate (0)
FunStuff Posts: 103 Rating: (10)	In general in order to capture correct data you need to havea cycle that is >2.5x the frequency that the value is being updated. For instance in your situation if you are updating the values in the plc every 1s than the hmi should be set to cyclic continuous 400ms or faster tag update for those values.
FunStuff Posts: 103 Rating: (10)
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12/9/2008 6:18 AM	Rate (0)
slaven Posts: 11 Rating: (0)	FunStuff In general in order to capture correct data you need to havea cycle that is >2.5x the frequency that the value is being updated. For instance in your situation if you are updating the values in the plc every 1s than the hmi should be set to cyclic continuous 400ms or faster tag update for those values. I don't think this is the way - if on PLC cycle is 1s and on WinCC 400 ms - then I'll have the same value twice look: 1s -\|_ _ _ _ _ _ _ _ _ _\| 400ms - \|_ _ _ _\|_ _ _ _\|_ _ _ _\| and the second problem is WinCC can scan tags every 100ms, but cant logging so often I need logging the value
slaven Posts: 11 Rating: (0)
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12/9/2008 1:27 PM	Rate (0)
ZAK Gold Member Joined: 5/8/2006 Last visit: 10/23/2025 Posts: 1085 Rating: (78)	Hi, WinCC flexiblecannot archive faster than 1 sec. That is system-related. If you want to archive for a short time you can use bittriggered trend with switch buffer. The data are stored in a data block. After the archive processthe stored datain DBcan be archivedin a csv filewith a WinCC flexible script. Maybe this FAQ will help you: http://support.automation.siemens.com/WW/view/en/21913875 Alternative you can use WinCC V6.2 SP2 or WinCC V7 because WinCC can archivetags every 500ms. If you need a faster archiving with WinCC (not WinCC flexible) you can use the following application: http://support.automation.siemens.com/WW/view/de/23780904 Bye

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12/9/2008 2:40 PM	Rate (0)
FunStuff Posts: 103 Rating: (10)	slaven FunStuff wrote: In general in order to capture correct data you need to havea cycle that is >2.5x the frequency that the value is being updated. For instance in your situation if you are updating the values in the plc every 1s than the hmi should be set to cyclic continuous 400ms or faster tag update for those values. I don't think this is the way - if on PLC cycle is 1s and on WinCC 400 ms - then I'll have the same value twice look: 1s -\|_ _ _ _ _ _ _ _ _ _\| 400ms - \|_ _ _ _\|_ _ _ _\|_ _ _ _\| and the second problem is WinCC can scan tags every 100ms, but cant logging so often I need logging the value I was refering to anti-aliasing rules regarding ensuring you capture each update. I wasn't aware that you only wanted to capture each update only once. If this is the case you will need to buffer the values in the plc and call a script at a lower frequency to write the values out to a file and allow the plc to overwrite the buffer once the file has been written.
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12/9/2008 2:49 PM	Rate (0)
slaven Posts: 11 Rating: (0)	Thanks for the links,thereare a lot of useful information. but my problem is the synchronizing cycles in a PLC and WinCC. It doesn't matter what cycle period (100ms or 1s), cause when the cycle-timeis the same in a PLC and WinCC from time to time Im reading the same value twice,and in the other hand lost one cycle value.
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12/9/2008 3:03 PM	Rate (0)
slaven Posts: 11 Rating: (0)	Ive done the buffer already, you know! but from time to time I lost the values. Now I didnt have the feedback from WinCC to a PLC about reading values, if I dont find the other way I will makea script for confirming reading. I agree with you that I need more intelligent client-sideapplication, I had this idea but thought about another way of synch
slaven Posts: 11 Rating: (0)
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12/9/2008 3:33 PM	Rate (0)
ZAK Gold Member Joined: 5/8/2006 Last visit: 10/23/2025 Posts: 1085 Rating: (78)	Hi, why do you not use the logging acquisition mode "On Change". So, thesystem can archive the data more oftenthan 1 second. Bye

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