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TON IEC-TMR SFB4 Zero Preset

Created by: JCrox at: 5/15/2008 12:40 AM (5 Replies)

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5/15/2008 12:40 AM	Rate (0)
JCrox Regular Member Joined: 4/29/2007 Last visit: 3/15/2021 Posts: 26 Rating: (1)	Hello, I know this is an old problem that seems to have been raised by many: I seem to have a problem with the operation of SFB4 when the preset (PT)is set to 0ms. Rather than completing immediately (Q = TRUE) on applying an input (IN = TRUE) it never completes. I've seen lots of threads regarding the operation of the timers within the PLC-SIM (which seem to have been resolved with the latest hotfix and / or version) but my problem relates to the operation of SFB4 in S7-300 and S7-400 CPUs. The problem occurs regardless of the OB in which the SFB is called (OB1 or OB3X). Any suggestions? Is this a known problem? Do I have to implement a workaround by putting the SFB4 in wrapper FB so that it operates as I would expect (I'd rather not)? I'd be really grateful for any help or info that people might have on this. John

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12/29/2010 3:53 PM	Rate (0)
ilker1 Posts: 5 Rating: (2)	I'VE SAME PROBLEM. ARE THERE ANY SOLUTION FOR THIS PROBLEM. MY PLC IS S7-315-2PN/DP.
ilker1 Posts: 5 Rating: (2)
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1/2/2011 6:46 PM	Rate (0)
Late Platinum Expert Joined: 1/7/2006 Last visit: 11/17/2023 Posts: 2705 Rating: (318)	Hello, When the time is started you can not change the time. When it starts then the internal time is read out and the time where it counts to is the starttime + the time wenn the "IN" parameter is high. See the example and then especially the VAT-table where you can see what is happening... Attachment TestTON.zip (280 Downloads)
	I hope that the answer will help, if you have still questions, don't hesitate to ask me. All the best, Late Never say never, think in solutions, not in trouble......
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1/2/2011 6:47 PM	Rate (0)
Late Platinum Expert Joined: 1/7/2006 Last visit: 11/17/2023 Posts: 2705 Rating: (318)	Hi, See my answer above!
	I hope that the answer will help, if you have still questions, don't hesitate to ask me. All the best, Late Never say never, think in solutions, not in trouble......
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1/3/2011 2:27 PM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/7/2024 Posts: 3026 Rating: (1057)	JCrox I seem to have a problem with the operation of SFB4 when the preset (PT)is set to 0ms. Rather than completing immediately (Q = TRUE) on applying an input (IN = TRUE) it never completes. Hello ilker1and belated hello JCrox as far as I'm aware, this is how the IEC Timers always behaved in an S7 and are supposed to behave. Put simple, a 0 Time Setpoint (PT) disables the Timer and switches theoutput Off. Not too sure if IEC 61131 stipulates this behaviour (don't have a copy of it handy) or if it is not described at all in it and this is simply Siemens implementation. Possible "Workarounds" would be toeither avoid a 0 Time Setpoint or tocreate logic to check the Time Setpointand then "bypass" the timer or to use an S5 Timer (which behaves differently). I hope this helps
	Last edited by: fritz at: 1/3/2011 2:44 PM Fixed up quote box Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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8/26/2013 3:27 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	There is a bug in SFB4 indeed. I had put the zero preset value and it never turned on. Step 7 v5.5, CPU 315-F latest version on market.

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