Always Off Bit

[Dayvieboy]

Found this online

Kind of funny

We use "Always Off" for Dummy Code to Monitor tags in the ladder
to avoid [AFI]'s from throwing warnings when compiling.

One would hope that you could find a few ways to mitigate the
"Worst Idea You Ever Had" from temptation

Just praying that Jon-Jon in maintenance don't get called to remote
in late night after in after a few pints of Guinness, could be dangerous
.

 

[dummy_bit]

 

[L33er]

Here is what I normally do at the Main sub:

--------------(L) Always_ON

---------------(U) Always_OFF

 

[joseph_e2]

I do something similar:

 

[BachPhi]

Here is what I normally do at the Main sub:

--------------(L) Always_ON

---------------(U) Always_OFF

I went a bit further with aliasing AFI tag to Always_OFF.

 

[cardosocea]

Here is what I normally do at the Main sub:

--------------(L) Always_ON

---------------(U) Always_OFF

It will still run for a cycle, no?

 

[Dayvieboy]

If you have different scan times on subroutines
neither the latch & unlatch as well as the persisted logic
will work all of the time.

 

[BachPhi]

Non-sense!

Try to toggle this:

 

[Dayvieboy]

Send me that code & I will show you how it only works in simple loops.

It works 100 % if at top of the program and more importantly.
only works if all programs are all in that one loop.

If you have one loop that scans & 20 ms
and another that scans @ 10 ms the 20 ms will fail often.

Put your counter in the 10 ms scan then play with the toggle.

 

[BobB]

I always use always on in front of a rung.
Easier to insert code rather than having to battle with redesigning the rung.
Also easy to make a normally closed rather than open if you do not want the rung to be scanned.

 

[Rson]

Love it!

 

[joseph_e2]

I always use always on in front of a rung.
Easier to insert code rather than having to battle with redesigning the rung.
Also easy to make a normally closed rather than open if you do not want the rung to be scanned.

Can you explain further please? I worked with some machines from Korea that had an always on bit be the first instruction on almost every rung, which puzzled me. How does that make code insertion easier? Is it platform specific? I'm really curious.

 

[BobB]

If using ladder and you many horizontal contacts coming away from the left of the rung and you wish to insert a single contact in front of them you basically have to redraw the rung.
if there is a normally on single contact and you wish to insert another single contact it is easy to insert between the always on and the vertical line in the ladder - saves a heap of time.

 

[ASF]

I'd hazard a guess that this applies most specifically to the Omron platform, as BobB is a bit of an Omron evangelist

AB does not have this limitation.

I have used some other platforms that have a similar limiation, but all I do in that case is copy the first contact on the rung, paste it into the space between the first and second instruction, and then change the first instruction to whatever I need my new instruction to be. Achieves the same thing without any redesigning!

 

[BobB]

ASF - not only Omron I can assure you. Many the same. Emerson is interesting by the way. Just doing a big job with their dual processor and Profinet ring jobbie.