Can First scan bit have a condition in Rslgoix

bornwild

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Join Date
May 2010
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Riyadh
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hello all,

I am trying to set up a latch bit like this S:FS----- true condition------OTL. I tried in rs emulator and it the bit latches but in actual compactlogix PLC when i download the program it does not latch.

The thing i am tryin to achieve is if you download the offline program and if the condition is true on the first scan the bit should latch .

Is it different in emulator and actual compactlogix.?
Is it different than contrologix?
 
Did you test it by dropping the PLC out of "Run" mode and then putting it back in "Run" mode? There aren't any real tricks with the S:FS bit.
 
bornwild said:
hello all,

I am trying to set up a latch bit like this S:FS----- true condition------OTL. I tried in rs emulator and it the bit latches but in actual compactlogix PLC when i download the program it does not latch.

The thing i am tryin to achieve is if you download the offline program and if the condition is true on the first scan the bit should latch .

Is it different in emulator and actual compactlogix.?
Is it different than contrologix?
Click to expand...

What is driving this "conditional" ?

Is it an input, or an internal bit ?
 
Hi.

I am actual evaluating actual time of the controller. I will post the screen shot in a while

Edit: I have the screenshot

SFS.JPG
 
Last edited:
Regardless of whether it is an Input or an internal bit, it doesn't make a scrap of difference, other than the internal bit needs to be "on" when the first-scan bit is used to test it, so the code driving it needs to be above the test rung.


I have tested this (ControlLogix), and it completely works ...

2019-04-26_082300.jpg
 
bornwild said:
Hi.

I am actual evaluating actual time of the controller. I will post the screen shot in a while

Edit: I have the screenshot
Click to expand...


Well that's not going to work... by the time the S:FS branch is scanned, the rung is already FALSE, and you can't make a false rung true again
 
From your rung it looks like you are attempting....

a: ... latch the bit if the processor re-starts in the same minute as it went off (Note, I did not say it has been off for less than one minute, because that won't be flagged if the processor went off at XHH:MM:59).

b: ... latch the bit if the processor re-starts before 13:00 hrs on the same day it went off.


In your own words, tell us what you are trying to capture
 
That processor isn't in Run Mode, or you are offline ...

The power rails are not green ...


Where is the GSV instruction that populates your TIME array ?


It needs to be executed before this rung for it to work ...
 
Last edited:
daba said:
That processor isn't in Run Mode, or you are offline ...

The power rails are not green ...


Where is the GSV instruction that populates your TIME array ?


It needs to be executed before this rung for it to work ...
Click to expand...

Daba. Thanks so much for the help. This is what the problem was. In the main routine. I have routine Test which has the program i need to latch and the GSV was placed after that and this why the bit was not set. Thanks again for your help

SFS2.JPG
 
I have a question about the purpose.

If this is to test if the first scan at powerup was within a minute of power down, then wouldn't you be moving the TIME values to "[Minute/Day/Hour]_Last_Recorded" DINTs (one for each value) then comparing the FirstScan time to the recorded integers?

The way you have it, comparing to specific numbers, it would only be true once in a lifetime, if it were powered up on exactly the right minute.

Unless CLXs can now edit their programs and change set values in compare instructions. Maybe all those plant managers were right - the PLC changed its program.
 
Aabeck said:
The way you have it, comparing to specific numbers, it would only be true once in a lifetime, if it were powered up on exactly the right minute.
Click to expand...


I had assumed he had just put those numbers in the code to test the operation of the S:FS and latch. I never thought for one minute it was the finished job.

Turns out it was rung order that let him down....
 

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