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How do I make /use a trigger on a negative flank

Created by: xmnj at: 8/4/2017 12:02 PM (8 Replies)

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8/4/2017 12:02 PM	Rate (0)
xmnj Gold Member Joined: 9/30/2016 Last visit: 11/19/2025 Posts: 952 Rating: (6)	I really ought to remember this but I don't and I can't find the answer here either - so here goes: I want to reset a SR flip/flop when a binary signal changes status and I only want a pulse (not a steady signal) I have tried with a N_TRIG (see attached screenshots) and the #Testbit_1 does switch between TRUE and FALSE but I am not getting any change at Q. What is wrong and how do I make it work ? Is there a smarter what to do this ? Attachment trigger.pdf (282 Downloads)

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8/4/2017 12:14 PM	Rate (0)
Sandeep Bakoliya Bronze Member Joined: 7/20/2015 Last visit: 12/23/2025 Posts: 154 Rating: (27)	xmnj I really ought to remember this but I don't and I can't find the answer here either - so here goes: I want to reset a SR flip/flop when a binary signal changes status and I only want a pulse (not a steady signal) I have tried with a N_TRIG (see attached screenshots) and the #Testbit_1 does switch between TRUE and FALSE but I am not getting any change at Q. What is wrong and how do I make it work ? Is there a smarter what to do this ? Hi xmnj Use P_TRIG to reset your OUTPUT Q If this post helped you, you may use the Rate-button Thanks & Regards: Sandeep Bakoliya
	Regards Sandeep Bakoliya
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8/4/2017 12:26 PM	Rate (0)
xmnj Gold Member Joined: 9/30/2016 Last visit: 11/19/2025 Posts: 952 Rating: (6)	Hi Sandeep Bakoliya, I have tried P_TRIG also - it made no difference. No matter if I had a P_TRIG or a N_TRIG I thought the Q pin would be activated at some point when I toggled the value of "Auto_IF".User.WinCC_STS."KE01 StBy Man Act" But nothing happens :-( Sandeep Bakoliya Hi xmnj Use P_TRIG to reset your OUTPUT Q Sandeep Bakoliya

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8/4/2017 12:36 PM	Rate (0)
mopS04 Posts: 5521 Rating: (1058)	hi xmnj, You did the negation of the signal twice. So it is the same like on the Set-comand, but with an edge(flank). Use a positive edge(flank) to reset the SR-element or change the "Auto_IF".User.WinCC_STS."KE01 StBy Man Act" to a Normally-Open-contact. hope this helps, regars,
mopS04 Posts: 5521 Rating: (1058)
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8/4/2017 1:14 PM	Rate (0)
xmnj Gold Member Joined: 9/30/2016 Last visit: 11/19/2025 Posts: 952 Rating: (6)	Hi mopS04, Thanks to you and Sandeep Bakoliya for answering. I just tried that and it does not LOOK like it is working either (see screenshots again) - but I am starting to think I need something more in the logic to achieve the desired functionality. I would like to be able to toggle with the input ("Auto_IF".User.WinCC_STS."KE01 StBy Man Act") and get the output ("Auto_IF".User.WinCC_STS."KE01 StBy Act") to toggle even then the input ("Auto_IF".User.WinCC_STS."KE01 Load StBy Act") is activated. In English I want to be able to switch the system out of StandBy by toggling the manual Standby even when the load-activated StandBy is on. Maybe if I use a SEL (can I use a boolean for 0/1 signals ?) and use the N_TRIG to make it switch between "Auto_IF".User.WinCC_STS."KE01 Load StBy Act" and a steady zero (and the OUT value goes to the SET pin of the SR in parallel with "Auto_IF".User.WinCC_STS."KE01 StBy Man Act" Any suggestions ? mopS04 hi xmnj, You did the negation of the signal twice. So it is the same like on the Set-comand, but with an edge(flank). Use a positive edge(flank) to reset the SR-element or change the "Auto_IF".User.WinCC_STS."KE01 StBy Man Act" to a Normally-Open-contact. hope this helps, regars, Attachment trigger 2.pdf (246 Downloads)
	Last edited by: xmnj at: 8/4/2017 1:14:50 PM Last edited by: xmnj at: 8/4/2017 1:48:20 PM
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8/4/2017 5:02 PM	Rate (0)
0_Einstein Grandmaster-Expert Joined: 7/7/2010 Last visit: 12/23/2025 Posts: 16325 Rating: (2520)	If you rework the problem with a set of -(s)- and -(r)- coils with a P-trig in front of each set condition, and likely the same for a reset, unless you have a hard reset (like no power or system wide fault prevents reset clearing). Then you create a unique -(s)- network for each individual situation that sets the output. The key is they only trigger the set once upon state change from off to on, using a P-Trig just to the left of the -(s)- Same for the reset. In this way, each sentence you wrote above for when you want to turn it ON gets a single network and a single SET coil. Same follows for reset. Using this approach will save considerable headache trying to achieve it with a single set/reset block. Sure it may be entirely possible to do that way, but it will be difficult to maintain once you do get it right. This approach makes it completely clear what cases turn it on, and turn it off. It also gets around all the potential order of solve or logic chasing you have to do.
	science guy
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8/7/2017 9:47 AM	Rate (0)
xmnj Gold Member Joined: 9/30/2016 Last visit: 11/19/2025 Posts: 952 Rating: (6)	Thank you huggy_d1, I am sure you are right that splitting it up in modules are the right way. How ever I must be somewhat slow since I am not really sure I know HOW it is you would restructure it. Would you restructure these networks ? If so then how ? The 3 different things (manual toggle button - calendar module - load conditions) that can set/reset the standby mode are already split up in separate networks ("Auto_IF".User.WinCC_STS."KE01 Load StBy Act" and "Auto_IF".Boilers.KE01.DigitalSignals."KE01-CM-StBy" and "Auto_IF".User.WinCC_STS."KE01 StBy Man Act") where each network sets a coil. That seems to be working. Should the coils in the 3 component networks ( ) be changed to (P) or (N) coils ? Would you use a P-TRIG on the input to the S/R flipflop in each of the 3 component networks ? The three coils are then used as inputs (are these called switches/negated switches ?) to set /reset a S/R flipflop - should I insert a P-TRIG in each of these lines. I am not sure how I can modularize / split up the setting of the output further since I only have one output I can set ("Auto_IF".User.WinCC_STS."KE01 StBy Act") ? I know I am asking a lot but a simple sketch would probably be helpful.

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8/7/2017 3:31 PM	Rate (1)
0_Einstein Grandmaster-Expert Joined: 7/7/2010 Last visit: 12/23/2025 Posts: 16325 Rating: (2520)	I am not saying this way is the only way to accomplish the task, but it does detect leading and trailing edge events rather than level detection. Each approach is appropriate for different types of problems. I find when I have level (multiple ON) states that turn something else on, and only one of them turns it off, I run into problems with level monitoring for a variety of reasons. I have seen HMI buttons stick on, or the program in the HMI is set to turn a bit on, and the plc is responsible for turning it off once it's turned on. Problem is when does it turn it off? Before or after my code that relies on it / expects it to be off? Order of solve problems are difficult so I try to avoid them. This is a way to handle your first S/R block. You can put all 4 in the same network if you like. It uses more bit, but all inputs to the S/R have a chance to turn on the output, but only one time. This makes the reset as an override because it can always override any single input because they are edge triggers. If this is not what your situation needs, then ignore it. Forgive the look, but it hopefully gets the idea across. Auto_IF.User. Auto_IF.User. WinCC_STS. WinCC_STS. KE01 StBy KE01 StBy Act Man Act ---\|p\|----------------------(s)---- Auto_IF.User. Auto_IF.User. WinCC_STS. WinCC_STS. KE01 Load KE01 StBy Act StBy Act ---\|p\|----------------------(s)---- Auto_IF.User. Auto_IF.User. Boilers.KE01 WinCC_STS. DigitalSignals. KE01 StBy Act KE01-CM-StBy ---\|p\|----------------------(s)---- Auto_IF.User. Auto_IF.User. WinCC_STS. WinCC_STS. KE01 StBy KE01 StBy Act Man Act ---\|n\|----------------------(r)---- xmnj Thank you huggy_d1, I am sure you are right that splitting it up in modules are the right way. How ever I must be somewhat slow since I am not really sure I know HOW it is you would restructure it. Would you restructure these networks ? If so then how ? The 3 different things (manual toggle button - calendar module - load conditions) that can set/reset the standby mode are already split up in separate networks ("Auto_IF".User.WinCC_STS."KE01 Load StBy Act" and "Auto_IF".Boilers.KE01.DigitalSignals."KE01-CM-StBy" and "Auto_IF".User.WinCC_STS."KE01 StBy Man Act") where each network sets a coil. That seems to be working. Should the coils in the 3 component networks ( ) be changed to (P) or (N) coils ? Would you use a P-TRIG on the input to the S/R flipflop in each of the 3 component networks ? The three coils are then used as inputs (are these called switches/negated switches ?) to set /reset a S/R flipflop - should I insert a P-TRIG in each of these lines. I am not sure how I can modularize / split up the setting of the output further since I only have one output I can set ("Auto_IF".User.WinCC_STS."KE01 StBy Act") ? I know I am asking a lot but a simple sketch would probably be helpful.
	science guy
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This contribution was helpful to 1 thankful Users xmnj

8/8/2017 1:44 PM	Rate (0)
xmnj Gold Member Joined: 9/30/2016 Last visit: 11/19/2025 Posts: 952 Rating: (6)	A very BIG thank you huggy_d1 - that is a big effort you made. I need to do some other thing the next couple of days - but I WILL study this carefully and try to apply it.

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This contribution was helpful to 1 thankful Users CS Moderator

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