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Old March 18th, 2017, 01:21 PM   #1
Bering C Sparky
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OSR /OSF in AB

Carry over from another post, but I was asked a question about how AB One Shots functioned on the AD Forum.

Here is the question I was asked:

Quote:
I'm not familiar with AB. Is the one-shot behavior an attribute of the element itself, rather than the instruction?
I answered the question:

Quote:
Yes exactly,
Each One Shot is a unique and individual tag. One Shots become True when the logic before them is True. Not when another instruction with the same tag is True elsewhere in the program.
In Allen Bradley, when a One Shot is placed on a rung, it requires all the instructions before it (to its left) on the rung, to be True in order for the Output to the right of the One Shot to become True for 1 scan.
But then I got to thinking........
I have never used OSR or OSF instructions in AB....only the ONS instruction.

Am I right to assume that the OSR and OSF instructions in Allen Bradley generally follow the same rules as far as, the logic on the rung before the One Shot instruction must be true in the case of the OSR and False in the case of the OSF for the One Shot to become True itself for one scan?

I always assumed that they followed the same general rules as the ONS in this way.

But now I see that AD software acts differently and the One Shot is not a unique tag but replicated from others in the program to function more as a one shot XIC or XIO (Rising / Falling) to a specific tag that is used elsewhere in the program.

Do the OSR and OSF instructions in AB at like the ones in AD also????
Or do they follow the same general rules as the ONS instruction????

I could dig out my old AB software and emulator and try it myself but was hoping someone would just give me the answer for free, so I can put this out of my mind and move on.

Thanks in advance.

BCS
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Last edited by Bering C Sparky; March 18th, 2017 at 01:48 PM.
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Old March 18th, 2017, 02:26 PM   #2
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I always refer to 'help' documentation on the instruction itself. I have found AB documentation to be fairly though.

Note that a few instructions vary based on the specific family being programmed. Be sure to check that.
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Last edited by bernie_carlton; March 18th, 2017 at 02:29 PM.
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Old March 18th, 2017, 04:00 PM   #3
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Slightly off-topic but, the Click PLC even allows a built in one-shot option for certain box instructions, for example - COPY and MATH. This would allow the elimination of a separate one-shot external to the instruction.

Notice the pulse symbol by the instruction type.
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Old March 18th, 2017, 04:26 PM   #4
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Guess I am not getting anything for free today.

No one wants to just give me the answer to the question and are going to make me work for it I guess.

I will look up the answer to my question online or dig out what little software I have for AB later and find out.

Just pulled into Dutch so going to be busy for a while.

BCS
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Old March 18th, 2017, 04:45 PM   #5
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ONS: Rung condition out is true for one scan if the rung condition in transitions from false to true.

OSR/OSF: rung condition out = rung condition in.
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Old March 18th, 2017, 05:11 PM   #6
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Quote:
Originally Posted by AustralIan View Post
ONS: Rung condition out is true for one scan if the rung condition in transitions from false to true.

OSR/OSF: rung condition out = rung condition in.

Thank you Australian, I appreciate the info.
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Old March 18th, 2017, 07:44 PM   #7
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here are some related threads ... if I get time tomorrow (not likely - I'm swamped these days) I'll give you a step-by-step breakdown ... actually it will have to be several breakdowns – because of the variations between the different Allen-Bradley platforms ... anyway - most (if not all) of the different ideas involved are covered in the following threads ...

http://www.plctalk.net/qanda/showthr...0&postcount=10

http://www.plctalk.net/qanda/showthr...27&postcount=4

http://www.plctalk.net/qanda/showthr...2&postcount=13

TIP: following through the continuing conversation presented in the last link above, should go a long way towards convincing you that you're not always going to be able to trust the "books" for subjects like this ... an operational test with the precise equipment is a much more reliable way to nail down the details ...
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Old March 18th, 2017, 11:15 PM   #8
Bering C Sparky
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Hi Ron,
Thanks for the info I appreciate your time.

BCS
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Old March 19th, 2017, 11:44 AM   #9
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I'm pretty sure that your main issue is that there are differences between how the Automation Direct software handles One-Shots - and how the Allen-Bradley software handles them ... what makes it even more challenging is that there are quite a few differences between how they get handled just by the various Allen-Bradley platforms ...

anyway - before you move on, you'll certainly want to consider how the "retentive" Latch/Unlatch instructions in Allen-Bradley differ from the Set/Reset instructions in Automation Direct systems ... many people think that these are directly interchangeable ... they are NOT ... and quite a few safety issues can arise when these are misused by programmers who don't really understand the differences ...

the following link should help ...

http://www.plctalk.net/qanda/showthr...86&postcount=1

man - has it been 12 years since I wrote that? ... it seems like yesterday ...
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Old March 19th, 2017, 07:33 PM   #10
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Ron,

I know I have read this post before, but its been years ago.
Now that I am actually working with Automation Direct devices it was good to read this again.

As always your post are very informative and helpful.

Thanks again,
BCS
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Old March 20th, 2017, 12:05 PM   #11
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Quote:
Originally Posted by Ron Beaufort View Post
the following link should help ...

http://www.plctalk.net/qanda/showthr...86&postcount=1

man - has it been 12 years since I wrote that? ... it seems like yesterday ...
Just reread it, surprised to find my first post in that thread. It's been a while...
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