Skip to Content

Register Login

Industry Online Support

Technical Forum

Navigation

FB: which is the best way to avoid output conflicts?

Created by: avafab at: 4/13/2012 3:07 PM (11 Replies)

Rating (1)

Thanks 2

Result pages:: |; 1 | 2; |

12 Entries

Entries per page: 10 | all

4/13/2012 3:07 PM	Rate (0)
avafab Posts: 83 Rating: (1)	Hello Sirs, I strongly would like to divide my station in little reusable units using FB but I would like to avoid conflicts on outputs (general PLC rule: each output must be set or reset only in one point of the program). For example when I want to drive an output Q0.1 that is already driven by other conditions I cannot put it directly connected to the output of the FB because it could be in conflict with other conditions, this force someone to make an eccessive use of merkers that goes from the output of FBs to the real output networks, but this is a bit frustratingand I don't like it. FB---(M350.0) and then --------\|M350.0\|---------------(Q0.1) Is there a best practice to avoid this, is there a simple way to connect output to FBs without using all those merkers or bits in DBs? If I put directly the output on the FB is there any way to avoid posible conflicts? thank you
avafab Posts: 83 Rating: (1)	Last edited by: avafab at: 4/13/2012 3:09 PM Last edited by: avafab at: 4/13/2012 3:08 PM
Suggestion To thank Quote Answer

4/13/2012 7:15 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 5/2/2023 Posts: 2957 Rating: (242)	Hi, I don't know if there is some general rules, but I have my own policy on setting outputs. For example, output Q0.0 opens a valve, but I have lots of conditions in whole program to open the valve. So every condition sets or reset temporary bit, lets say M0.0 and lets say I have 5 points in my program where I need to control the valve so it turns out that I have M0.0, M0.1, M0.2, M0.3 and M0.4 bits which controls valve. Then I have one function which controls all physical outputs (Qx.x) and the final conditions to open valve looks like this: [code] O M0.0 O M0.1 O M0.2 O M0.3 O M0.4 = Q0.0 [/code] Hope you understand what I wanted to tell you
	Best regards, Darius
Suggestion To thank Quote Answer

4/14/2012 7:17 AM	Rate (0)
TIBI68 Gold Member Joined: 12/1/2009 Last visit: 5/2/2023 Posts: 669 Rating: (146)	Hi, you need to usethe IN,INOUT, OUT, STAT & TEMP paramerters in you function block instead of programing withdirect addresses within your FB. Afteryou just call the block with different I/O's. Regards. Maybe you can upload us your project so that we understand what you mean exactly? I can recommend you theprogramming book's from HANS BERGER.
	Last edited by: TIBI68 at: 4/14/2012 7:24 AM Give us your feedback and show us your respect! We take our free time to support you with our knowledge and experience. If this post is helpfull to you kindly click on "Rate" or "Thank".
Suggestion To thank Quote Answer

4/16/2012 7:17 AM	Rate (0)
Aret Posts: 2348 Rating: (259)	There are a lot of designs that can be taken into consideration. Anyway you can make control check via cross-reference (Ctrl+Alt+R in Simatic manager)
Aret Posts: 2348 Rating: (259)
Suggestion To thank Quote Answer

4/16/2012 8:50 AM	Rate (0)
avafab Posts: 83 Rating: (1)	Please have a look here: http://www.slideshare.net/DMCChicago/dmc-siemens-summit-2011-top-ten-programming-mistakes-slide-share-8588695 from slide 38 to 47. These guys suggest us to not make an improper use of merkers. So I understood that the common solution is to use some merkers that are in AND with only one coil but I would like to avoid it, because it makes the symbolic confusing (quite the same name for every merker that goes into a single coil) So, at this point I modify a bit my question: I have a FB only for a unit automatic cycle, then I need to call the same outputs some else where to make the manual movements. This means that the FB and the network to make manual movements are going to drive the same output. If I use the same output for ex. Q0.0 at the end of the FB and at the end of manual movement network, is there the possibilty to generate a conflict? (for conflict I mean when the same output is set and immediately reset in the same PLC cycle scan by different networks with the result that no movement is done.) If I decide to deactivate the FB when I need to make manual movement and viceversa (manual/auto mode are mutual exclusive) is this conflict avoided? goal: I don't want to replicate outputs using mekers in shared memory, I don't want to use merkers.
avafab Posts: 83 Rating: (1)
Suggestion To thank Quote Answer

4/16/2012 10:27 AM	Rate (0)
TIBI68 Gold Member Joined: 12/1/2009 Last visit: 5/2/2023 Posts: 669 Rating: (146)	Yes, if you deactivate always one FB. Meaning if you call either FB MANUALOR FB AUTOMATIC you can use sameoutputs twice without conflicts. But what you should be awareof is: The switching between the two blocks should not have any disturbance on your process. Regards.
	Give us your feedback and show us your respect! We take our free time to support you with our knowledge and experience. If this post is helpfull to you kindly click on "Rate" or "Thank".
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users avafab

4/16/2012 11:21 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/5/2023 Posts: 2966 Rating: (1025)	Hello avafab I personally don't have a problem with using "merkers" as and when needed. These are after allsimply a predefinedinternal memory area and there is nothing "dangerous" about them (even though the DMC presentation seems to suggest there is). I appreciate though that you do not want to use them, so my question concerning yourrequirement is: avafab I have a FB only for a unit automatic cycle, then I need to call the same outputs some else where to make the manual movements. This means that the FB and the network to make manual movements are going to drive the same output. Why not simply have the "Unit's" automatic and manual movement related logic combined inside the one FB?
	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.
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users Lucky123

4/16/2012 1:18 PM	Rate (0)
avafab Posts: 83 Rating: (1)	Thank you, you are right! but in my case, our customer give us these unit without manual mode (with know-how protection), so we have to develop software for manual mode. So.. it seems that I need to use merkersthe problem is that when I look at the simbolic table all those merkers cofuse me because their names are quite the same and I think it will be confusing for technicians that will work on the project after me.
avafab Posts: 83 Rating: (1)
Suggestion To thank Quote Answer

4/16/2012 1:34 PM	Rate (0)
TIBI68 Gold Member Joined: 12/1/2009 Last visit: 5/2/2023 Posts: 669 Rating: (146)	Hi, I don't know how big is your project, but you should consider a complete new software anyway. What CPU are you working on? Are the protected blocks written in SCL? Regards.
	Give us your feedback and show us your respect! We take our free time to support you with our knowledge and experience. If this post is helpfull to you kindly click on "Rate" or "Thank".
Suggestion To thank Quote Answer

4/16/2012 2:05 PM	Rate (0)
avafab Posts: 83 Rating: (1)	s7-300, blocks in ladder/stl
avafab Posts: 83 Rating: (1)
Suggestion To thank Quote Answer

|

Share this page:

Share this page on...

Follow us on