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Problem in calculation of Scan Cycle time by FC 34

Created by: Mohammad Razmjoo at: 5/17/2022 10:03 AM (2 Replies)

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5/17/2022 10:03 AM	Rate (0)
Mohammad Razmjoo Posts: 99 Rating: (0)	Hi there, I tried to calculate "scan cycle" by means of SFC1, SFC20(BLKMOV), FC34(SB_DT_DT) in OB1.But when I monitor that result value, it is swingy between e.g. 10(Hex: a) and 11(Hex: b) for this time I recorded in video I attached, while the "current scan cycle time" in module information is 10ms as you see in the video. Why the result value is swingy??! What can I do?! Here's my STL: network1: A( O I 0.0 O Q 0.0 ) A I 0.1 = Q 0.0 network2: CALL "READ_CLK" RET_VAL:=MW2 CDT :=#CDT_1 NOP 0 SET FP M 80.0 JC A1 CALL "SB_DT_DT" DT1 :=#CDT_1 DT2 :=#CDT_2 RET_VAL:=#Int_output NOP 0 L #Int_output T MD 100 A1: CALL "BLKMOV" SRCBLK :=#CDT_1 RET_VAL:=MW6 DSTBLK :=#CDT_2 Attachment Action to Scan Cycle.avi (583 Downloads)
Mohammad Razmjoo Posts: 99 Rating: (0)
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5/18/2022 1:10 PM	Rate (2)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 1/13/2026 Posts: 5154 Rating: (772)	Mohammad Razmjoo Why the result value is swingy??! The result is what it is. Mohammad Razmjoo What can I do?! Use OB1_PREV_CYCLE.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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5/18/2022 2:11 PM	Rate (1)
mopS04 Posts: 5521 Rating: (1058)	hi Mohammad Razmjoo, Use the information from the OB1 local data as already suggested. Your code is completely unnecessary. Operating system does the same thing for you and provides the result in OB1 local data. Unstable times can come from other tasks the PLC has to do, like communication. But I wouldn´t say that is unstable. it is just switching in the one last digit. so the cycle time is maybe about 10.5ms hope this helps, regards,
mopS04 Posts: 5521 Rating: (1058)
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